SYSTEM 7550 ESU and ABC Modes Service Manual

LIMITED WARRANTY For a period of two years following the date of delivery, CONMED Corporation warrants the CONMED System 7550 Electrosurgical Generator against any defects in material or workmanship and will repair or replace (at CONMED’s option) the same without charge, provided that routine maintenance as specified in this manual has been performed using replacement parts approved by CONMED. This warranty is void if the product is used in a manner or for purposes other than intended.

© 2006 CONMED Corporation 525 French Road Utica, New York 13502 U.S.A.

U.S. Patent Numbers 4,437,464 - 4,569,345 - 4,617,927 - 4,727,874 - 4,848,335 - 4,961,739 - 5,152,762 5,626,575 and other patents pending. For Technical Service or Return Authorization Phone: 303-699-7600 / 1-800-552-0138 Extension 5274 Fax 303-699-1628 For Customer Service or to order parts phone: 1-800-448-6506 / 315-797-8375 / Fax 315-735-6235 or contact your CONMED Representative. European Authorized Representative MDSS GmbH Burckhardtstr 1 D - 30163 Hannover Germany The revision level of this manual is specified by the highest revision letter found on either the inside front cover or enclosed errata pages (if any).

Manual Number 60-7552-ENG Rev. D 10/06 Unit Serial Number_________________________________

Table of Contents & List of Illustrations

Section

Title

Page

1.0 2.0 3.0 4.0 5.0 6.0

General Information ...Refer to Operator’s Manual (P/N 60-7551) System Components ... Refer to Operator’s Manual Operation... Refer to Operator’s Manual Operator Service ... Refer to Operator’s Manual Technical Information ... Refer to Operator’s Manual Circuit Descriptions ... 6-1

6.1 6.2

Introduction ... 6-1 Display Panel Assembly [A5] ... 6-1

6.3

Power Control Assembly [A4] ... 6-5

6.4

High Voltage Power Supply [A7] ... 6-9

6.5

HV/Flow Control Assembly [A1] ... 6-11

6.6

Argon Flow Control [A1] ... 6-13

6.7

Full Bridge Amplifier [A8] ... 6-15

6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.2.6 6.2.7 6.2.8 6.2.9 6.2.10 6.2.11 6.2.12 6.2.13 6.2.14 6.2.15 6.2.16 6.2.17 6.3.1 6.3.2 6.3.3 6.3.4 6.4.1 6.4.2 6.4.3 6.4.4 6.5.1 6.5.2 6.6.1 6.6.2 6.6.3

General Information ... 6-1 Mailbox [U19] ... 6-1 Power Adjustments [U16 & U33] ... 6-1 Activation Requests [U16 & U33]... 6-2 Mode Select Encoders [U31 & U32] ... 6-2 Display Drivers - Seven Segment [U14, U20, U39, U40, U41, & U17] ... 6-3 Indicator Driver [U34] ... 6-3 Firmware [U28 & U1]... 6-3 RAM [U2 -6116]... 6-3 A/D Inputs [Control Microcontroller] ... 6-3 A/D Inputs [Monitor Microcontroller] ... 6-4 EEPROM & Driver [U37, U27] ... 6-4 D/A Converter [U12] ... 6-4 Keyboard Scanner [U5] ... 6-5 5V Monitoring [U29] ... 6-5 Output PIA [U21] ... 6-5 T_MON [U35] ... 6-5 Power Control - Full Bridge Amplifier ... 6-6 RF Logic [U7 on the Power Control Assembly] ... 6-7 Power Control - I/O Signals ... 6-8 ABC™ Arc Sense ... 6-8 Power Supply Topology ... 6-9 Phase Control Output ... 6-9 HVPS Isolation Components ... 6-10 HVPS Low Voltage Components ... 6-11 Line Synchronization Circuit ... 6-11 HV Regulation Control Loop ... 6-12 Pneumatic Circuit... 6-13 Mass Flow Rate Regulation ... 6-14 Smart Sense... 6-15

Section

Title

6.8 6.9 6.10 6.11

Single-Ended Amplifier [A9] ... 6-16 RF Output Assembly/Components [A10] ... 6-17 Low Voltage Power Supply [A6] ... 6-18 HS/A.R.M. Assembly [A11] ... 6-18

7.0

Maintenance/Checkout ... 7-1

6.11.1 6.11.2 6.11.3 6.11.4 6.11.5

7.1 7.2 7.3 7.4 7.5 7.6 7.7

Page

Handsense Circuit ... 6-18 Aspen Return Monitor (A.R.M.) ... 6-19 RF Leakage Monitor... 6-20 Transformer Select Relays... 6-20 Arc Sense Transformer ... 6-20

Introduction ... 7-1 Cleaning ... 7-1 Generator & Mobile Storage Assembly... 7-1 Access to Circuits & Factory Settings ... 7-2 Default Settings (Factory Settings) ... 7-2 AC Mains Frequency & Voltage ... 7-2 Initial Setup & Test ... 7-3

7.7.1 7.7.2 7.7.3 7.7.4 7.7.5 7.7.6 7.7.7

Accessory Connections ... 7-3 Display Panel Testing ... 7-3 Activation Testing ... 7-5 RF Output Power Checks ... 7-5 Argon Flow Testing ... 7-6 Remote Power Control Testing ... 7-6 Return Monitor (A.R.M. - Aspen Return Monitor) ... 7-7

8.0

Calibration ... 8-1

7.8 7.9 7.10 7.11

Pulsed Cut Mode ... 7-8 RF Leakage Test ... 7-8 Final Checks ... 7-8 Mobile Storage Pedestal (Cart) ... 7-8

8.1 8.2

Introduction ... 8-1 Equipment List ... 8-1

8.3 8.4

Calibration Set-Up ... 8-1 A.R.M. Calibration (HS/A.R.M. Assembly - A11) ... 8-1

8.5

High Voltage Calibration (HV/Flow Control Assembly - A1)... 8-2

8.6

Argon Flow Calibration (HV/Flow Control Assembly - A1) ... 8-2

8.7

Power Calibration ... 8-3

8.2.1 8.2.2 8.2.3

8.4.1 8.4.2 8.5.1 8.5.2 8.5.3 8.6.1 8.6.2 8.6.3 8.6.4 8.7.1 8.7.2

Standard Equipment List ... 8-1 Optional Calibration Equipment List ... 8-1 Test Leads & Adaptors ... 8-1

10 Ohm A.R.M. Calibration ... 8-1 150 Ohm A.R.M. Calibration ... 8-2 HV RAMP Calibration ... 8-2 High Voltage Adjust ... 8-2 HV_MON Adjust ... 8-2 dP Calibration (Differential Pressure) ... 8-2 PABS Calibration (Absolute Pressure) ... 8-2 Flow Rate Calibration (Optional) ... 8-2 FMON Calibration ... 8-3 Filter Calibration - Full Bridge Modes (Optional) ... 8-3 Cut Power Calibration (Power Control Assembly - A4) ... 8-3

Section

Title

Page

8.7.3 8.7.4 8.7.5 8.7.6 8.7.7

Pinpoint Coag Calibration (Power Control Assembly - A4) ... 8-3 Spray Coag Calibration (Power Control Assembly - A4)... 8-3 Bipolar Calibration (Power Control Assembly - A4) ... 8-4 ABC Calibration (Power Control Assembly - A4) ... 8-4 ABC Over Voltage Calibration (Power Control Assembly - A4) [Optional]... 8-4

8.8

EEPROM Calibration ... 8-4

8.9

IEC RF Leakage Measurement [Optional] ... 8-5

8.8.1 8.8.2 8.8.3

Appx. A Appx. B

Appx. C

Spray Coag PW_MEA Loading ... 8-4 ABC PW_MEA Loading ... 8-4 A.R.M. Max Voltage Loading ... 8-4

Mnemonic List ... A-1 Troubleshooting Guide ...B-1 Introduction ... B-1 Control Microcontroller Failure Codes and Troubleshooting Tips... B-2 Monitoring Microcontroller Failure Codes and Troubleshooting Tips ... B-3 Additional Troubleshooting Tips (Non-Error Code Related) ... B-5 Error Storage and Retrieval ... B-7

Error Display Configuration ...B-7 Example Error ...B-8

Schematics & BOMs ... C-1 Bill of Material: Chassis & Cart ... C-1 Bill of Material: HV/Flow Control PCB Assembly ... C-2 Bill of Material: Power Control PCB Assembly ... C-4 Bill of Material: Display PCB Assembly ... C-5 Bill of Material: LV Power Supply PCB Assembly ... C-10 Bill of Material: HV Output PCB Assembly... C-11 Bill of Material: FB Amplifier PCB Assembly ... C-12 Bill of Material: SE Amplifier PCB Assembly ... C-13 Bill of Material: RF Output PCB Assembly ... C-14 Bill of Material: ARM/Handsense PCB Assembly ... C-15

Figure/Title

Page

Figure 6.1 RF Drive Signals ... 6-8 Figure 6.2 Line Sync/RAM ... 6-11 Figure 6.3 Flow Diagram ... 6-14 Figure 6.4 Resistance vs. Bargraph ... 6-19 Figure 7.1 Test Adapters ... 7-9 Figure 7.2 Test Analyzer Connections ... 7-10 Figure 3.1 RAMP Flat Spot ... 8-2 Figure 3.2 IEC Method RF Leakage Test Setup ... 8-5 Figure B-1 Signal Status for a Handcontrol 1, Cut Activation Request ... B-9 Figure B-2 Signal Status for ABC® Activation... B-10 Figure C-1a Assembly Location Diagram... C-1 Figure C-1b Pneumatic Assembly...C-1 Figure C-2 Interconnect Diagram ...C-1 Figure C-3 A1 HV/Flow Control PCB ...C-2 Figure C-4a A1 HV/Flow Control PCB Schematic, Sheet 1 (of 2) ... C-2 Figure C-4a A1 HV/Flow Control PCB Schematic, Sheet 2 (of 2) ... C-3 Figure C-5 A4 Power Control PCB ...C-4 Figure C-6 A4 Power Control PCB Schematic ... C-4 Figure C-7 A5 Display PCB ...C-5 Figure C-8a A5 Display PCB Schematic, Sheet 1 (of 4) ... C-6 Figure C-8b A5 Display PCB Schematic, Sheet 2 (of 4) ... C-7 Figure C-8c A5 Display PCB Schematic, Sheet 3 (of 4) ... C-8 Figure C-8d A5 Display PCB Schematic, Sheet 4 (of 4) ... C-9 Figure C-9 A6 LV Power Supply PCB ...C-10 Figure C-10 A6 LV Power Supply PCB Schematic ... C-10 Figure C-11 A7 HV Output PCB ...C-11 Figure C-12 A7 HV Output PCB Schematic ... C-11 Figure C-13 A8 FB Amplifier PCB ...C-12 Figure C-14 A8 FB Amplifier PCB Schematic ... C-12 Figure C-15 A9 SE Amplifier PCB ...C-13 Figure C-16 A9 SE Amplifier PCB Schematic... C-13 Figure C-17 A10 RF Output PCB ...C-14 Figure C-18 A10 RF Output PCB Schematic ... C-14 Figure C-19 A11 A.R.M./Handsense PCB ... C-15 Figure C-20 A11 A.R.M./Handsense PCB Schematic ... C-15

Circuit Descriptions Section 6.0

6.1

Introduction

The information on the System 7500™ circuits identifies specific signals and I/O ports that help identify the appropriate signal levels. The text uses the word SET for high and CLEAR for low. To locate the assemblies within the System 7500™, refer to Figure C-1. Use the system interconnect (Figure C-2) to identify wiring harness terminations and individual signals within a harness.

6.2

Display Panel Assembly [A5]

6.2.1

General Information

The System 7500™ has two 80C550 microcontrollers with one dedicated to system control and the other dedicated to system monitoring. The control microcontroller (U15) sets the system enables and control limits, while the monitor microcontroller (U22) monitors system performance and sets “inhibits” when an error is detected. Both of these devices have “on-board” A/D converters, and each device independently monitors separate analog signals. The address, data and control buses of both microcontrollers are isolated by a device called the “mailbox”, U19, a dual port RAM that allows two-way data transfer between the two microcontrollers. On the schematic, the signal labels will have either a “C” or “M” attached. The “C” is for the controller logic (U15) or control microcontroller and the “M” is for the monitor logic (U22) or monitor microcontroller interface. The schematic for the display panel (Figure C-8) is on four separate sheets. Sheet 1 is the schematic for the displays and drivers only; sheet 2 shows all the connectors that are on this assembly along with some discrete non-logic circuitry; sheet 3 is the control microcontroller logic; and sheet 4 is the monitor microcontroller logic. This assembly has several programmable logic devices to interface signals to the data bus for both the control and monitor microcontrollers. During the discussion when two reference desig-

nators are listed together it means the logic functions are the same and can be interchanged. 6.2.2

Mailbox [U19]

A dual port logic device that allows data transfer between the two microcontrollers. All system setups and messages are communicated through the mailbox between the two microcontrollers. When data is loaded by either microcontroller, a bit labeled DA (data available) is SET to inform the other microcontroller that it has mail. Once the data is read from the mailbox, another bit labeled DC (data cleared) is CLEARED to inform the sender that the mail has been retrieved. Each microcontroller has independent access to the mailbox and the mailbox is the only component that connects the two data buses. Each instruction sent through the mailbox requires two bytes of information with the first byte (command byte) identifying the instruction and the second byte (data byte) containing the data for the instruction. 6.2.3

Power Adjustments [U16 & U33]

(C for controller; M for monitor) Power adjustments on the System 7500™ are made by rotating the power control encoders. The mnemonics for the power encoders are: CT - CUT; CG - COAG; BP - BIPOLAR; BM - ABC™. Each encoder is a two bit counter (i.e.; CT0 & CT1) where the two counts are used to identify the direction of rotation. The logic devices (U16 & U33) store the previous count and compare it to the new count in order to recognize if the count is increasing or decreasing, which defines if the encoder is rotated clockwise or counterclockwise. Each “click” of the encoder is a count and the number of counts are stored within U16 & U33 until the microcontroller reads the port. The microcontroller reads each encoder port independently and if an encoder has been rotated, the count will be greater than zero. The data the micro will see is a number (0 to 32) representing the number of “clicks” the encoder has been rotated and a separate bit that signifies the direction of the count, either up or down. The microcontroller then takes this count and adds or

6-1

subtracts it to the existing power value.

A_T: Active Mode or Target Mode

The control microcontroller reads and controls power change requests, however the monitor microcontroller also looks at the encoders to verify the change is valid. If the two microcontrollers disagree on the direction (up or down), number of counts, or which encoder is rotating, the power will not be changed; i.e. the change request is ignored.

ABC™ mode and used for tone selection only. A_T SET, tone is 500 Hz and ABC™ is active - A_T CLEARED, tone is 250 Hz and ABC™ is in the Target mode.

6.2.4

Activation Requests [U16 & U33]

BRN_OUT: Brown Out Holds high for at least 6 seconds when power fails and is used to identify a temporary power loss. The user settings are returned following a temporary power loss.

Activation requests are “looked at” by both microcontrollers, and if the two do not agree on an activation request, an error code (Err 303 or Err 307) will be displayed.

Tone_A: Tone Signal

Activation Requests: Handcontrol or Footcontrol

KB_DA: Keyboard Data Available

H2CT

Handcontrol 2, Cut, Active Low

H2CG

Handcontrol 2, Coag, Active Low

H1CT

Handcontrol 1, Cut, Active Low

H1CG

Handcontrol 1, Coag, Active Low

HIP

Handcontrol, Bipolar, Active Low

FCT

Footcontrol, Cut, Active High

FCG

Footcontrol, Coag, Active High

FBIP

Footcontrol, Bipolar, Active High

FAB

Footcontrol, ABC™, Active High

Note: HABC Handcontrol is activated at handcontrol 2 and is a result of H2CT * H2CG * HABC_DR, which is an output of U16. 6.2.5

Mode Select Encoders [U31 & U32]

Blend Level (BL) and Argon Flow (FL) rate is adjusted by the same type of encoders as used for power adjustments. The logic within U31 & U32 for these two encoders is the same as for power adjustment and the discussion for power adjustment applies here. These logic devices have I/O ports also, and the following text provides a brief description of each port signal. U31: Port B (PB0 - PB7) Inputs for Control Microcontroller LPSW: Low Pressure Switch SET when the argon tank pressure is less than 240 psi. Low Tank warning is illuminated. FDEV: Flow Deviance SET if an occlusion occurs to the argon flow.

6-2

Mode Activation and Alarms. Square wave signal with frequency between 250 Hz to 1KHz for audible tone. SET when a front panel switch is pressed, cleared when the device is read. U31: Port C (PC0 - PC6) Outputs from Control Microcontroller ABC>80: ABC™ Power is Greater than 80W SET when ABC™ power is set to greater than 80W. CLEARED when ABC™ power is 80W or less. RFEN: RF Enable SET to enable the RF drive for all activations. FB_EN: Full Bridge Enable CLEARED when activation for Cut, Blend, Pinpoint, & Bipolar occurs. OV_TST: Over Voltage Test Test pin that allows the control microcontroller to test and verify the ABC™ over voltage circuit is operational. During Power-On SelfTest (POST), this signal is clocked for a duration of about 7mS. Alarm: Tone for alarms 1KHz signal tone for alarm - volume cannot be adjusted. Tone_B: Tone, Mode Signal for all Tones except alarm tones. Volume can be adjusted. U32: Port B (PB0 - PB7) Monitor Inputs This port has the switch for setting the system defaults. The switch is located on the back side of the Display PCB for accessibility. Default settings are with the switch in the “OFF” position (off = high on the input pin of U32). To change a default setting, move the appropriate switch to the

“ON” position. To verify the selection, turn the power off for at least 10 seconds, and then restore power. 1-TEST-RUN (Default: RUN MODE) TEST mode allows the system to be operated without error detection and shut down. This mode can be changed anytime while the system is in standby. Test mode can be selected before the unit is powered on, however the “store” button must be held down until an “Err 1” is displayed. Test mode is to be used only for system level testing. 2-SIN-DUAL PAD (Default: DUAL PAD) SIN is for single foil return electrodes. 3-ZERO-LAST (Default: LAST SETTING) When ZERO is selected, all power levels will default to zero when the system is powered on. Last setting only applies to power levels of the default modes. 4-SPRAY-PPT (Default: PINPOINT COAG) Spray Coagulation can be selected as a default mode. 5-NON_SIM-SIM (Default: SIMULTANEOUS) When the switch is set for non-simultaneous activation, dual activation will not occur for coag modes. 6-GAS TEST (for testing purposes only) Allows the ABC™ mode to be tested without argon gas connected. Can only be set after the unit has been powered on and completed initialization. U32 - PORT C: Outputs from Monitor This port has three (3) active outputs only and the outputs are used solely to inhibit internal circuits when a system fault is detected. GAS_En: Gas Enable SET to enable argon gas flow - CLEAR inhibits argon gas flow. Drives the solenoid valve that is part of the argon flow control manifold. HV_INH: High Voltage Inhibit SET inhibits the HV to the amplifiers. RF_INH: RF Drive Inhibit CLEAR inhibits the RF Drive to the amplifiers. 6.2.6 Display Drivers - Seven Segment [U14, U20, U39, U40, U41, & U17] Converts Hex to Seven-Segment. The hex value on bits 0-3 drive the “ones” digit; the hex value

on bits 4-7 drive the “tens” digit; and the hex value on the address (A0, A1) is used to drive the “hundreds” digit. The displays are common anode, therefore each segment is illuminated with an active low on the drivers. The digits are multiplexed, allowing only one digit to be on at any one time for each section. 6.2.7

Indicator Driver [U34]

All indicators on the display panel with the exception of the numeric displays are driven with this logic device in a 4x7 matrix. The outputs labeled S0-S3 are multiplexed at a 25% duty cycle and these outputs are converted to 15V at U38 & U42, which provide drive current for all LED indicators. U9 and U10 sink the current for the indicators. The monitor microcontroller loads 4- eight bit registers, with each bit dedicated to a specific display panel indicator. The outputs S0S3 are “send” and the outputs labeled R0-R7 are “receive”. All the send and receive outputs are active high at a 25% duty cycle. 6.2.8

Firmware [U28 & U1]

The firmware or program for the control microcontroller is stored in U1 and the program for the monitor microcontroller is stored in U28. 6.2.9

RAM [U2 -6116]

U2 is the external RAM for the control microcontroller only and the monitor microcontroller only uses internal RAM. 6.2.10 A/D Inputs [Control Microcontroller] Only four of the 8 internal A/D inputs are utilized, and three of these inputs are for the A.R.M. (Aspen Return Monitor). 2VARM: A voltage that represents the resistance of the patient plate. ARM_10: Calibration limit for 10 ohms. (See A.R.M. cal) ARM_150: Calibration limit for 150 ohms (See A.R.M. cal) FMEA: Back pressure monitoring for argon gas flow. The control microcontroller monitors this signal as a means of detecting occlusions or special accessories with small orifice sizes. When the monitor microcontroller senses an error at ARM_10 or ARM_150, it will display an error code to identify which input has the fault. These are fatal errors that require the system to be reset

6-3

when they occur. An error for 2VARM is a return electrode fault and occurs when the resistance measured on the return electrode is not within specified limits for either a single or dual foil return electrode. An error code is not displayed, however the “red” indicator for a return electrode fault is illuminated. In many cases, intermittent or continuous alarms associated with these signals can be rectified by going through the calibration procedure for A.R.M. FMEA has an idle voltage of one-half of the value of PABS. When testing or troubleshooting, use the calibration procedure for PABS to determine the value of FMEA when no argon flow is occurring. This voltage increases with flow. A voltage that exceeds 3.3V in all flow modes will set a flow alarm by illuminating the “red” Flow Fault indicator. 6.2.11 A/D Inputs [Monitor Microcontroller] Seven of the eight available inputs are used for monitoring system signals. A failure with any one of the inputs will be displayed as an error code. HV_MON: High Voltage Power Supply Monitoring This A/D input is 200mV±40mV when the system is in the idle mode. The resolution is 20mV/V or 20mV for every volt on the +DC & -DC terminals of the High Voltage power supply. Calibrated for 1V with 50V on the High Voltage Power Supply. IMEA: Current Measure A ratio of the output current that is applied to the patient when Cut, Blend, Pinpoint or Bipolar modes are used. Used in conjunction with the HV_MON to determine the output power. F_MON: Flow Monitor The current through the flow control valve represents the flow rate. A flow rate that exceeds requested flow by more than 2 SLPM will set an alarm and inhibit both RF Output and argon flow. This signal is calibrated for 2V with a flow setting of 4 SLPM. PW_MEA: Pulse Width Measure Spray and ABC™ modes only. A DC average of the RF Drive pulse width to the single ended amplifier. In ABC™, the voltage increases as the power increases if a load is connected to

6-4

the ABC™ output. In Spray, the voltage is constant for all dial settings. FB_MON: Full Bridge Monitoring Cut, Blend, Pinpoint and Bipolar modes only. A DC average of the full bridge RF Drive. With Cut activated, FB_MON is approximately 2.85V and for each blend, the voltage is about 225mV less than the previous blend or cut mode. 10V Reference: The 10V reference is monitored and must be 4.46V±.2V. 15V Supply: The system 15V for control circuits is monitored. This voltage is used for op amps, relays and flow control valves. This voltage must be 3.72V±.5V. 6.2.12 EEPROM & Driver [U37, U27] The EEPROM (U37) is used to store user settings and these settings are recalled when the unit is first powered on or if a 5 second brown out occurs. On power-up, power settings will be the last settings for the default modes. Included in the EEPROM are the calibration limits for ABC™ and SPRAY PW_MEA settings. A failure detected with the EEPROM during system initialization will default all power settings to “0”. A failure detected with the PW_MEA stored data will inhibit the system from being used until the problem is corrected. U27 is a parallel-to-serial interface device. The EEPROM is loaded serially, however the PCF8584 allows the control microcontroller to load the serial data from the parallel data bus. 6.2.13 D/A Converter [U12] The D/A converter is used to control the following: •High Voltage (VCON) •Output Power (PCON) •Maximum voltage at each dial setting (ILIM) for Cut, Blend, Pinpoint, & Bipolar Modes •Argon Flow Rate (VGAS). Each of these signals should be zero volts in the idle mode and increase as the power or flow increases. The voltages listed below are the maximum limits at full power settings.

VCON = 9V when HVDC is 200V (0V-9V)

Handcontrol 1 - Cut or PPT. Coag

31h

Handcontrol 1 - Spray Coag

51h

Handcontrol 2 - Cut or PPT. Coag

32h

Handcontrol 2 - Spray Coag

52h

6.2.14 Keyboard Scanner [U5]

Argon Beam Coagulation

08h

The 74C922 allows a 4X4 matrix keyboard to be connected. When a Front Panel switch is pressed, the location of the switch is latched into the device and the signal KB_DA (keyboard data available) is SET. Only one switch press is stored and gets cleared after the device is read.

Bipolar

A0h

Footcontrol - Cut or PPT. Coag

34h

Footcontrol - Spray

54h

PCON = 8.8V at full dial cut (0V - 8.8V) ILIM = 3.8V at full dial cut (0V - 3.8V) VGAS = 6.2V at 10 SLPM (.15v to 6.2V)

6.2.15 5V Monitoring [U29] U29 is a microcontroller supervisory device that automatically sets the “RST” when the 5V supply is less than 4.5V. A short interruption of the mains power will cause a system reset to occur. On the input of U29 (pin 1) is a comparator (U35) that will cause a reset to occur if the 5V exceeds 5.7V. The pin “RST” is active high and “/RST” is active low.

PORT C: CIRCUIT ENABLES The following signals are SET during activation as shown: PSRQT: Power Supply Request Enables the high voltage power supply circuit Enabled for all mode activations. PC_EN: Power Control Enable Enables the Power Control Circuit to interface with the HV Control Circuit for Power Control when Cut, Blend, Bipolar or Pinpoint modes are activated. LVT_EN: Low Voltage Triac Enable

6.2.16 Output PIA [U21] Dedicated output PIA for the control microcontroller to latch control logic to system functions. This device has three (3) output ports and each will be described briefly. PORT A: CON_D0 - CON_D7 Dedicated for mode identification to the Power Control Assembly. When a mode activation occurs, the controller latches a Hex count into this register and the magnitude of the count identifies to the RF Logic FPGA which mode is being requested. Cut: 39h

Blend 1: 37h

Blend 2: 35h

Blend 3: 33h

Blend 4: 31h

Blend 5: 29h

Blend 6: 27h

Blend 7: 25h

Blend 8: 23h

Blend 9: 21h

Bipolar: 6Fh

PPT: 43h

Spray: 82h

ABC™: C3h

PORT B: OUTPUT RELAY SELECT These outputs connect to a relay driver (U23) on this PCB Assembly. Upon an activation, hex counts are latched into this register for relay closure dependent on mode and method of RF activation.

Enables the low voltage triac (125V) when Cut, Blend or Bipolar are activated. HVT_EN: High Voltage Triac Enable Enables the high voltage triac (185V) when Pinpoint, Spray, or ABC™ are activated. AR_EN: Argon Enable Enables the flow control circuit when ABC™ is activated. 6.2.17 T_MON [U35] The monitor microcontroller verifies that for every activation of RF Output, a tone is generated. T_MON is a signal with the same frequency as the tone generated.

6.3

Power Control Assembly [A4]

This assembly controls output power of all modes and has the driver logic for both RF Amplifiers. It is important to remember that this system has two separate RF Amplifiers and each amplifier operates in a different manner. The amplifier against the back wall is called Full Bridge (FB) and is used for Cut, Pinpoint, Blend, and Bipolar Modes. The other amplifier is against the side wall and is only activated for Spray and ABC™ modes. This discussion will focus on each amplifier independently.

6-5

6.3.1

Power Control - Full Bridge Amplifier

Output power in the Full Bridge modes is controlled by monitoring the output voltage and current, multiplying the two together and the product of the operation is power. The measured power is then compared to the requested power and if the power is greater than requested power, the power control circuit reduces the HVDC. If the power is less than the requested power, then the power control circuit increases the HVDC. The power control loop encompasses several assemblies, however we will only focus on the circuits of the Power Control Assembly. For this discussion, it is important to refer to the schematic (Figure C-6). The RF Output can be constant current, power regulated or a fixed output voltage, all depending on the RF load. The inputs labeled VSN (voltage sense) and ISN (current sense) are ratios of the RF output voltage and current that is delivered to the patient. U1 & U3 are RMS-to-DC converters that convert both signals to a DC level so they can be monitored and controlled. The DC level is then connected to the input of a unity gain amplifier (U2). U2 is used to control both voltage and current limits outside of the load regulation range. For the time, we will focus on the simpler aspect of this circuit, and cover the limits later in the discussion. Power regulation can be seen on the load curves that are within this manual. (See Figure 5.1.10, Pure Load Curves) Using Pure Cut as our mode for discussion, the output power is regulated between 300 ohms to 1K ohms. When the RF load is between 300 ohms and 1K ohms, the outputs of the amplifiers connected to U1 & U3 are negative, or the diodes D4 & D3 are reverse biased. The DC value of the RMS-to-DC converters is passed around the amplifier to the cathodes of D4 & D3, where they are buffered by the unity gain amplifiers, U2. U12 is a multiplier that multiplies the measured voltage (VSN) and measured current (ISN) together for a product term called POWER (P=VI). On the output of U12 is an amplifier (U10) with a potentiometer (RA5) in the feedback. This potentiometer is used to calibrate the gain of the loop and it is this potentiometer that is adjusted for Pure Cut calibration. The output of the amplifier (U10) is called measured power and the measured power is compared to the requested power PCON at V10D. The difference of the

6-6

two is called PERR (Power Error), a signal that can increase or decrease the HVDC for power control. When the signal is positive, the HVDC is reduced and when negative, the HVDC is increased. Digressing back to the outputs of the RMS-toDC converters for a moment, the DC value of the output voltage and current are both connected to the inverting input of the unity gain amplifiers. As long as the load is within the defined limits for power regulation (300 ohms - 1K ohms), the measured value will exceed the reference level or the level on the non-inverting inputs. The output of the amplifier is then negative, reverse biasing D3 & D4 diodes, and the output of the RMS-DC converters is passed through the 2.7 ohm resistors. The signal called ILIM is actually a reference. When the output current is less than this reference, the ILIM value is used as the multiplier with the measured voltage. ILIM is dependent on the dial setting, however for each dial setting it is fixed and becomes a fictitious representation for the output current. ILIM is multiplied against the measured voltage and the product is compared to the requested power. With a fixed current being compared to a fixed power setting, the result is a fixed voltage on the RF output. For loads that are greater than the loads for power regulation (R>1K ohms in cut), the RF output voltage is fixed (V=P/I). On U2-3 (VLIM) is a reference voltage that is really a fictitious value for the output voltage. For heavy loads (R<300 ohms in Cut), the output voltage is less than this reference so the value is multiplied against the measured output current. The product of the two is then compared to the requested power. With a fixed voltage (reference) and a fixed power setting, the output current is fixed (I=P/V). The resistance for power regulation drops with power setting, meaning at full power the load is 300 ohms but at 100 watts, the load is 100 ohms. Calibration of the Power Control circuit is set in Pure Cut initially by adjusting RA5. This potentiometer calibrates the loop gain for accurate power monitoring and control. Blend modes are a direct function of Pure Cut and do not need to be calibrated, however Bipolar and Pinpoint do require calibration. Bipolar is calibrated by adjusting RA6 and Pinpoint is calibrated by adjusting

RA7. The signal labeled PCON (power control) is driven from the DAC on the Display PCB and is the control voltage for output power. The range for PCON is 0V-9V. IMEA is a ratio of the output current measured, scaled from 0V to 4V maximum. IMEA allows the monitor microcontroller to monitor the output current. Too much output current will cause RF to be inhibited and an error code displayed. FB_EN is “cleared” by the control microcontroller anytime that Cut, Blend, Bipolar, or Pinpoint are activated. This signal enables the power control circuit when cleared. With FB_EN set, an offset is placed on the non-inverting input of the differential amplifier, causing PERR to be greater than 0 volts, which in the event of a failure, would force the HVDC to be low. PERR was covered earlier but as a reminder, this signal is the difference between the measured output power and requested power. When PERR is positive, the HVDC is decreased and when negative the HVDC is increased. 6.3.2 RF Logic [U7 on the Power Control Assembly] U7 is an FPGA, programmable logic device that is used to develop the RF amplifier drive signals for all modes. This device will be described with respect to the I/O only. Listed below is a brief description of the I/O on U7. COND0 - COND7 (Control Microcontroller Inputs) The hex count on these inputs select which RF amplifier will be driven and sets the right drive signals for the mode. The eight signals are latched into U7 when an activation request is made. (See display panel description for hex values as related to modes requested.) RF_CLK (RF Clock - input) A 1MHz clock for RF drive timing. Runs continuously. RF_INH (RF inhibit - input from monitor microcontroller) When CLEARED (low), RF is inhibited. CLEARED when no activation is requested or if a failure is detected.

FB_EN (Full Bridge Enable - input from control microcontroller) CLEARED when Cut, Blend, Pinpoint or Bipolar modes are requested. A CLEARED is required to enable output power control. OV_TST (Over voltage test - input from control microcontroller) A test pin used only to test the ABC™ Over Voltage circuit during system initialization by a series of pulses that simulate an ABC™ over voltage condition. After the test is conducted, the signal is latched low. A/T (Active/Target - output to control microcontroller) ABC™ mode only - A high occurs when ABC™ is in the ACTIVE mode; a low occurs when ABC™ is in the TARGET Mode. For tone control only as the two modes have distinctive tones. BM>80 (Beam greater than 80W - from control microcontroller) SET when ABC™ power is greater than 80W. An internal limit in U7 for switching from active to target mode. RFEN: (RF Enable - input from control microcontroller) SET to enable RF Drive to the amplifiers. RST: (Reset - from system reset signal) A SET causes internal latches to CLEAR. CT_PCON: (Cut Power Control voltage select) SET when Cut or Blend modes are activated . Switches Pcon for Cut. CG_PCON: (Coag Power Control voltage select) SET when Pinpoint is activated. Switches Pcon for Pinpoint. BP_PCON: (Bipolar Power Control voltage select) SET when Bipolar is activated. Switches Pcon for Bipolar. SE_PCON: (PCON for Spray & ABC™ active select) SET for Spray or ABC™ active only. Switches in Pcon for Spray and ABC™ active. BM_BST: (ABC™ Booster voltage control level) SET to enable Boost Pcon. BM_TAR: (ABC™ Target voltage control level) SET to enable Target Pcon.

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SP_PCON: (Scaler to calibrate Spray power) SET for Spray activation to rescale SE_Pcon for Spray calibration and control. T_RLY: Tank Relay selects either the Spray or ABC™ transformer primary. set when Spray is activated.

of about 200nS. FB2 RST follows FB2 DRV and has a pulse duration of about 200nS. SE_DRV: (Single Ended Drive) RF drive for the single ended amplifier. This signal is active when Spray and ABC™ modes are active. ��� �

XSLO: Transformer Sense input must be low. If the harness from the Handsense PCB to the Power Control PCB is not connected or broken, this signal is pulled up and will inhibit single ended operation. A_SNS: Arc Sense - A pulsed signal that pulses high anytime the ABC™ output exceeds a reference level. Four or more pulses indicates an open circuit on ABC™ and less than four pulses indicates the ABC™ output is loaded. ABC_OV: ABC™ Over Voltage Pulses if the ABC™ output exceeds 3500 Vpk and 192 consecutive pulses will cause ABC™ to be inhibited. If a failure occurs that latches ABC™ in the Active Mode, this signal will inhibit RF at power levels greater than approximately 45W.

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Figure 6.1 RF Drive Signals 6.3.3

Power Control - I/O Signals

The following signals are in addition to those described for U7. PW_MEA: Pulse Width Measured An average DC voltage of the Spray and ABC™ drive cycles. The Monitor microcontroller verifies that the measured pulse width is correct for the power setting.

SE_EN: Single Ended drive control.

FB_MON: Full Bridge Monitor

When this signal goes low, it allows C10 to start charging up and RF drive to the Single Ended Amplifier occurs.

An average DC voltage of the Full Bridge Amplifier drive to allow the monitor microcontroller a means of verifying the duty cycle of the RF drive.

SE_PW: Single Ended Pulse Width RF drive to the Single Ended Amplifier starts when SE_EN goes low and stays on until this signal transitions high. When this signal transitions high, RF drive is terminated for one cycle. FB1 & FB2 DRV: (Full Bridge drive) RF drive for the Full Bridge Amplifier. The full bridge amplifier requires two drive signals that are 180° out of phase with each other. The rate is 461KHz and the duty cycle of the signal varies with the mode requested. These signals are active in Cut, Blend, Bipolar, and Pinpoint. FB1 & FB2 RST: (Full Bridge Drive Reset) Reset signals for the amplifier drive transformers on the full bridge amplifier. The FB1 RST follows the FB1 DRV and has pulse duration

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IMEA: Current Measured The monitor microcontroller verifies that the output current is within limits. 6.3.4

ABC™ Arc Sense

ABC™ has two modes - Active and Target. The active mode is enabled when a load is sensed and only in the active mode will the power control dial have any effect on the output voltage or power. When a load is not present, the target mode is enabled where the RF Output voltage is fixed and the repetition rate increased. The Target mode also has two modes - Target Pulses and Booster Pulses. The ABC™ mode is quite similar to Spray in the sense that the output is a damped sinusoidal waveform. The waveform is heavily damped when a heavy load is on the output and lightly damped

with a light load. The degree of dampening is used to determine if a load is present or not. Refer to Figure C-6 and locate the input labeled +ASEN. This signal is a ratio of the primary current on the ABC™ output transformer. ASEN is compared to a reference voltage at U15-3 and each peak of the damped waveform that exceeds this reference level will cause the output of U15 to switch high at the same frequency as the output (570KHz). If the output of U15 has four pulses for one cycle (1 cycle is 35uS active/60uS target), the logic within U7 assumes a load is not present and the system remains in the Target mode. However, if less than four pulses are detected for one cycle, the logic within U7 assumes a load is present and switches to the active mode. Staying with the signal ASEN, it is also connected to a comparator (U16). This comparator is used for ABC™ over-voltage detection. Without going into significant detail, if the output of U16 pulses 192 consecutive cycles, the logic within U7 assumes the system has locked up in the active mode and the RF is inhibited. Note that the inverting input of this comparator has a potentiometer (RA9). This potentiometer allows calibration of the over voltage limit, and should ABC™ fail to initiate, it may be necessary to refer to the calibration section for this adjustment. The target and booster pulses are a means of limiting RF leakage by controlling both the output voltage and repetition rate when the output is not loaded. Both modes are fixed outputs, meaning the power setting has no influence on the output voltage. The resistor ladder (R24, RA4, R17, & R19) sets the limits for both the target and booster modes. Target has 1032 pulses with a peak voltage of approximately 1800Vpk, and then the booster is switched in. The booster mode has 32 pulses with a peak voltage of 6000Vpk and these pulses are used to ionize the argon gas to assist with initiation. When a load is not detected during the booster pulses, then the target/booster cycle is repeated until a load is sensed. The voltage level of each mode is selected by U4 with BM_TAR for target and BM_BST for booster. These two signals should toggle on and off when ABC™ is activated without a load on the output. When a load is sensed, SE_PCON is set and now the power setting determines the pulse width and the logic reduces the repetition rate from 60uS to 35uS. Output power is controlled by pulse width

and the pulse width controller is U5 and Q2. For the start of each cycle of ABC™, Q2 is turned off and this allows C10 to charge linearly. When the charge of C10 exceeds the PCON voltage on U5-3, the output of U5 switches high and terminates the pulse time. Now is a good time to bring up Spray. Spray Coagulation and ABC™ are quite similar, only Spray is lower power and does not have the target modes. The output power in spray is controlled by HVDC, and the pulse width in spray is fixed at about 1.3uS. Calibration of Spray is performed by adjusting RA3, which simply scales PCON down for a pulse width that will correct the output power to match the dial setting.

6.4

High Voltage Power Supply [A7]

The High Voltage Power Supply (HVPS) provides variable regulated DC voltage and current to the RF amplifiers which converts this energy into high frequency surgical current. The HVPS is contained on two separate circuit board assemblies. The High Voltage output assembly contains the power devices and capacitive filters which provide the high voltage output. The HV/Flow Control assembly generates the control signals required to regulate the high voltage output and performs other high voltage related tasks. This section will be specific to the high voltage assembly and the control circuit for the high voltage will follow. 6.4.1

Power Supply Topology

The HVPS is a phase controlled type power supply. With this topology, output voltage is controlled by varying the phase angle at which the AC mains sinusoidal waveform is permitted to conduct. Typically, a triac or SCR in series with the incoming AC line is off during the rise of the mains sinusoidal waveform. Following the peak of the waveform, a trigger is asserted at the gate allowing the triac or SCR to turn on and the line voltage present at the triggered phase angle is available to charge filter capacitors commonly used with these topologies. The phase angle triggering sequence occurs for each subsequent half cycle of the sinusoidal waveform. 6.4.2

Phase Control Output

Referring to the High Voltage Output schematic (Figure C-12), the line isolated AC voltage enters the printed circuit assembly at J1-1 (AC Hi), J1-3

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(AC Lo), and J1-4 (AC Com). We should note that these AC signals are isolated from AC Mains by means of an isolation transformer located in the generator assembly. The AC signals are transformer taps with AC Lo rated for 125V and AC Hi rated for 185V with a nominal voltage input. Referring once again to the schematic, Q3 & Q7 are triacs that are triggered by opto couplers U1 or U4 when the HVPS is enabled. Q3 is selected when Spray, Pinpoint or ABC™ modes are activated and Q7 is selected for Pure Cut, Blend, and Bipolar modes. The resistor and capacitor that are connected from MT2 & MT1 are snubbers for switching energy and the remaining discrete components contribute to the generation of the trigger pulse. The trigger pulse from the opto couplers (U1 & U4) occurs at phase angles of approximately 80° to 170° of the AC waveform. Following the triacs are two separate bridge rectifiers (B1 & B2). The rectified signal from the bridges is then filtered by C13 & C14 which results in a DC voltage. Resistor R18 is a bleed resistor that will dissipate the energy from the filter capacitors. The schematic shows two test points (TP1 & TP2) that are labeled +HV and -HV. The voltage on these two test points is the regulated DC and is referred to as HVDC. Connecting an oscilloscope to the +HV and -HV test points would show a voltage with 120 Hz ripple, and the magnitude of the ripple depends on the load. A heavy load on the output means a high ripple rate on the HVDC test points. These test points have easy access and are a good place to connect a DVM when troubleshooting a system that does not have any RF Output. A system failure detected by the monitor microcontroller and some hardware circuits will typically inhibit the HVDC as a means of shutting down the RF output. The high voltage triacs (U1 & U4) of this assembly are only enabled when the system is activated for RF output, otherwise the voltage at TP1 & TP2 is an idle voltage of 10V. Referring on the schematic to TP1, a 33 ohm resistor and a fuse are shown in series with a MOSFET, Q8. This transistor is switched on following each RF deactivation to dump the charge from the filter capacitors (C13 & C14) and bring the HVDC back to, or near, idle voltage. The fuse would be the weak link of this power supply. Each time an activation request is termi-

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nated, the voltage on HVDC is dumped through this fuse. If the fuse opens up, then the only means of discharging the HVDC is through the bleed resistor R18. 6.4.3

HVPS Isolation Components

Digressing momentarily, this assembly has three optically isolated triac drivers, one opto coupler, and two isolation “sense” transformers. These components isolate the High Voltage Output circuit from the High Voltage Control circuit. The System 7500™ has two intermediate circuits that are both isolated from ground (chassis ground) and both are also isolated from each other. When using a voltmeter or oscilloscope on these circuits, it is imperative that the ground reference be connected to “-HV” of this circuit or the signal ground of the control or low voltage circuit. The signal grounds of the control circuit are not common to the -HV ground of this circuit. The triacs are fired when the cathode of the triac drivers are pulled to signal ground. The diode of these drivers is common with, and controlled by, the HV Control circuit. A short pulse of current through the diode of the triac driver switches on the gate of the triac at a phase angle that is greater than 80°. The triac will remain on until the AC signal is at approximately zero volts. The optocoupler (U5) is controlled by the HV Control Circuit and it switches on Q8 when the cathode of the diode is pulled low. When U5 is energized, the emitter goes high which switches on Q9; switches off Q10; allowing approximately 14V to switch on the gate of Q8. Pulling the cathode of U5 back high switches off U5, allowing Q9 to be switched off and Q10 to pull the charge from the gate of Q8 and switch it off. Following each RF activation (system is unkeyed), Q8 is switched on for approximately 100mS to allow R33 to dissipate the energy stored in the filter capacitors. The two sense transformers (T1 & T2) transfer a proportional ratio of the HVDC across the isolation barrier to the HV Control circuit. T1 provides what is called the HV sense for control and T2 provides the HV sense for monitoring. Both circuits and transformers are the same and the ratio of voltage transferred is the same. The purpose for the monitoring circuit is a means of verifying the controlling circuit is operating properly.

6.4.4

HVPS Low Voltage Components

The NPN transistor, Q6, provides the supply voltage for the low voltage components on this assembly. The voltage source for Q6 is the AC LO, where R26 limits the current and the zener diode (12V) sets the voltage on the cathode of D6 at about 10V. This 10V is used to provide the supply voltage to U3 & U2 of this assembly. The monitoring circuit will test for this 10V, and should a failure occur where this voltage is too high or too low, the system activation will be terminated. The sense transformers are driven at about 40 KHz by U3 & U2 with the outputs Q and /Q out of phase by 180°. The sense transformers are set up for a center tapped push-pull drive signal. When the top transistors (Q1 & Q5) are ON, they pull current from the center tap to ground which produces a signal on the secondary. The top transistors then switch OFF and the lower transistors (Q4 & Q2) switch ON, reversing the current through the primary and reversing the polarity on the output.

6.5

HV/Flow Control Assembly [A1]

The HV/FLOW Control assembly provides two unrelated unit functions. High Voltage Power Supply (HVPS) control and Argon Flow management circuits are both on this assembly. The schematics (Figures C-4a and C-4b) for this assembly are on two pages with the high voltage control schematic and the argon flow control schematic on separate sheets for clarity.

in a specific DC voltage at light loads (RL>1K ohms), and then the DC voltage will be reduced for heavier loads (RL<1K ohms) for power regulation. The HVPS & HV Control circuit make up a control loop, and a control circuit loop by nature feeds on itself such that one action in the loop results in another action, which results in another action, etc. 6.5.1

Line Synchronization Circuit

For this section, refer to Figure C-4a. The high voltage power supply (HVPS) is phase controlled and must be synchronized with the AC line voltage. The synchronization is accomplished by the zero crossing detector (U5-7) that is driven by F_LN (J3-13), a replica of the AC Line Voltage which comes from the low voltage line transformer secondary. The sine wave of F_LN is converted to a square wave at U5-7 and this results in a 50µS pulse at U10-4. The lower trace of Figure 6.2 shows the 50µS trigger pulse that is synchronized with zero crossing. The upper trace represents a ramping waveform that is ultimately used to initiate the HVPS triac trigger. The generation of the “cyclic ramp” waveform is accomplished with a circuit loop. The components of the loop will be covered in the next few paragraphs. To provide a simple description of this circuit, we will start at the voltage divider with the switch, S1 (RA7, R66, R67, & R68). The switch (S1) is set for either 50Hz or 60Hz operation. To the right of S1 is a precision clamp (U7B & U7C) with diodes on the outputs. The outputs of the precision clamps, if viewed with an oscilloscope, are a square wave with a rate of “Line Frequency x 2” or 120Hz when the line frequency is 60 Hz. A precision clamp will control the anode of the output diode to the lowest voltage on the two inputs. With 0V on the inverting (-) input, the anode of the output diode will be 0V and when the inverting input switches high (5V), then the anodes of the output diodes have the same voltage as S1-C (3V @ 60 Hz or 2.5V @ 50 Hz).

Figure 6.2 Line Sync/RAM The HVPS that is controlled by this circuit has a variable DC voltage (HVDC) that is dependent on the dial setting and the load. Power regulation of the System 7500™ is accomplished by controlling the HVDC where each power setting results

Following the precision clamp is a differential amplifier (U7A) with a gain of .9 on the noninverting input (U7-3), and unity gain on the inverting input (U7-2). The differential amplifier controls the direction of charge on the RAMP so that when the output of the differential amplifier is positive (3.2V), the RAMP discharges or ramps

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from 10V to -1.4V, and when the output of the differential amplifier is negative (-4V), the RAMP charges from -1.4V to 10V. The output of the comparator U5-1 provides the trigger for the gated Flip-Flop (U11A, U11B, U12A, U12B). As the RAMP charges in the positive direction and exceeds the 10V on U5-2, the output (U5-1) switches high, which causes a trigger pulse for the Flip-Flop (U11-2 & U12). The Flip-Flop outputs (U12-3 & U12-4) toggle causing the RAMP to discharge, and as the RAMP drops to less than 10V, the output of the comparator (U5-1) switches back low. Using an oscilloscope on U5-1 and the RAMP, the output switches high for a short duration at the “peak” of each positive RAMP cycle, providing a clock pulse for the flip-flop circuit and each clock pulse causes the RAMP to switch between charging and discharging. 6.5.2

HV Regulation Control Loop

The High Voltage Power Supply ( HVDC) and Control Circuits are part of the power control loop. This discussion will not go into the power control loop, but instead it will focus on how the power control loop works with this circuit. Let us start the discussion at the inputs labeled HV_SNS (high voltage sense), J1-1. The HV_SNS connects to the high voltage power supply (HVPS) and is a ratio of the HVDC. The HV_SNS comes into this circuit on J1-1 & J1-2 as a 40KHz square wave that proportionally corresponds to the HVDC. The HV_SNS signal is filtered and then converted to a DC voltage with a precision rectifier (U4C, U4D & associated components). To calibrate the HVDC requires only a single adjustment to the “loop gain” and this is done at RA4 (labeled HV ADJ). The amplifier U4B is a non-inverting amplifier (U4-7) with an output that is proportional to the HVDC at 45mV/V. (1V/.045V = 22 HVDC.) This signal will be referred to as the “measured HVDC”. A differential amplifier (U4A) is used for the difference between the measured voltage and requested voltage (VCON is referred to as requested HVDC). When the output U4-1 is positive, the measured voltage exceeds the requested voltage and causes the high voltage to be reduced. When U4-1 is negative, then the requested voltage is greater than the measured voltage and the HVDC is increased.

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VCON is driven by a DAC that is located on the Display Panel and has a range of 0V to 9V. In all modes except ABC™, VCON increases as the power setting is increased. In ABC™, VCON is fixed at 9V, where 9V of VCON results in 200V on the high voltage power supply. The input signal labeled PERR (NOTE: PERR originates on the Power Control Assembly - product term of the output voltage and current) is used to control the HVDC for power regulation and it will override VCON, but only to reduce HVDC. PERR cannot increase HVDC greater than the requested HVDC by VCON. PERR is active for Cut, Blend, Bipolar & Pinpoint Coag only and it is part of the power regulation loop. The analog switch U9B switches PERR into the circuit whenever one of the four listed modes is activated. The output of U9 (PERR) ties into the voltage control loop using a precision clamp (U3B), which will pass on to the anode of the output diode (D2), the highest voltage of the two inputs. When the output power exceeds the requested power, PERR is positive and will be passed through D2, which puts a positive voltage on the input to the integrator U3C. The same applies when the measured HVDC is greater than requested HVDC at the Differential Amp (U4A) output. A positive voltage on the input of an integrator will result in a negative integrator output, which reduces the HVDC. The output of the integrator (U3C) is a positive voltage and is used as a reference on a comparator U5D. On the non-inverting input (U5-12) of the comparator is the RAMP that is synchronized to the AC Line. Each time the RAMP on U5-12 exceeds the reference voltage on U5-13, it causes the output of the comparator to switch from low to high. The purpose for the NAND function (U12C) insures the triac trigger cannot occur before the ramp transitions downward, thereby limiting the triac triggering range to the values of 80 to 170 degrees. U12-10 triggers U14-4 on the rising edge which results in a pulse of approximately 100uS on U14-6. U14-6 triggers the selected triac driver according to the mode activated. The high voltage triac (HVTR) is selected for Pinpoint, Spray, and ABC™, while the low voltage (LVTR) is selected for Cut, Blend, & Bipolar modes. These two signals are active LOW.

To enable the correct triac, the signals HVT_EN (Pinpoint, Spray & ABC) or LVT_EN (Cut, Blend, & Bipolar) must be high. These signals originate on the Display Board Assembly.

front panel, and is user controlled by the ABC™ power setting in the Automatic mode, or by the user specified flow rates in the Manual and Endo Modes. VGAS has a range of 0.7V to 6.2V.

Referring to the schematic (Figure C-4a), a signal labeled LK_CON can also reduce the HVDC. VCON is the HVDC requested voltage, however PERR (power error) can override VCON and reduce the HVDC to a lower voltage if measured power is greater than requested power in Cut, Blend, Bipolar and Pinpoint modes only. LK_CON can also reduce HVDC if the RF Leakage exceeds calibrated limits (see calibration section). RF Leakage is typically not a problem in any mode except Spray, and then only when no load is on the output. Should the RF Leakage exceed calibrated limits of 140mA (200 ohm load), then this signal is positive with respect to ground which causes a reduction in the HVDC. When Spray mode has a load, then leakage is not an issue and the HVDC returns to the VCON set point. To sum up, PERR can override and reduce voltage in Cut, Blend, Bipolar and Pinpoint only. LK_CON can reduce HVDC in all modes except ABC™.

Argon Modes and Flow Rate Ranges (liters per minute): Automatic Mode

1.0 - 10 lpm

Manual Mode

0.5 - 10 lpm

Endo Mode

0.1 - 4.0 lpm

The Mass flow regulator is a closed loop system. The requested mass flow rate is compared with the requested flow rate and the result is an error signal that adjusts a servo controller to either increase or decrease the argon flow. To understand the circuit, we will first identify the pneumatics which the circuit operates. 6.6.1 Pneumatic Circuit

Transistor Q1 has a label HVR (High Voltage Reset) attached, and is enabled following each activation. HVR switches on a transistor of the HVPS that pulls the voltage down to idle in a time of about 100mS.

See Figure 6.3 for this section. Tank pressure indicated on the pressure gauge, located on the rear of the cart, is indicative of the quantity of remaining argon gas. A low pressure pneumatic/electric switch connected to the high pressure tank line closes if the tank pressure falls below approximately 240 psi. Closure of this switch is used to warn the user of minimal remaining gas supply in the tank, indicated on the unit front panel by illuminating the yellow “low tank” indicator in the ABC™ section.

The last section of this circuit to be covered is the HV Monitoring. Note on the schematic the inputs labeled HV_MON, followed by a precision rectifier. This circuit is an exact duplicate of the HV_SNS signal previously discussed on both this assembly, and also on the HV power supply assembly. A ratio of the HVDC is sampled at HV_MON; filtered and rectified for a DC voltage on the cathodes of the output diodes. The resistors R9 & R6 divide the monitored voltage down by one-half so that it will not exceed 5V. U1B is a non-inverting amplifier that is calibrated for 1V when the HVDC is at 50V. The resolution of this signal is 20mV/V, or for each 20mV measured on U1-7, the HVDC is 1V.

The high pressure of the argon tanks is reduced to approximately 30 psi by a pneumatic regulator. If for any reason, pressure downstream of the pneumatic regulator should exceed 50 psi, a safety relief valve opens to minimize the risk of excessive pressure in the low pressure lines. Continuing downstream of the pneumatic circuit, a solenoid valve opens during ABC™ activation periods. This valve acts as a safety valve where it can be closed to shut argon flow off, if necessary. The proportioning valve is the controller for argon flow (solenoid and proportioning valve are on a common manifold) that increases and decreases gas flow as a result of the control signal developed by the control electronics.

6.6

Immediately following the pneumatic manifold is a dampener to reduce any oscillations of the gas flow that may occur. The next element in the low pressure pneumatic circuit is the sensing orifice, recognizable by the five (5) ports for argon tubing connections. The sensing orifice is a calibrated

Argon Flow Control [A1]

See Figure C-4b for this section. The argon gas flow control circuitry provides control functions to produce a regulated argon gas mass flow rate at the ABC™ handpiece tip. The requested mass flow rate (VGAS) signal originates on the unit

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Figure 6.3 Flow Diagram restriction that provides flow rate information back to the flow control circuit. This orifice is the pneumatic equivalent of a current sense resistor. The differential pressure across the orifice is proportional to the flow rate, or simply, an increase in the flow rate increases the differential pressure as measured across the calibrated restriction. Three hoses from the sensing orifice connect back to the flow circuitry. Two of the hoses provide differential pressure information, while the third hose provides atmospheric pressure information. The atmospheric pressure information is used to compensate for usage at various altitudes. Lastly, the argon gas is filtered prior to delivery to the ABC™ handpiece accessory.

microcontrollers on the display assembly. Each of the microcontrollers have control and monitoring responsibilities for argon flow. The Control Microcontroller sets the flow rate with Vgas (.5V - 6.2V) and enables the circuit with a SET on AR_EN. The Control Microcontroller can also monitor a predicted flow at FMEA. The Monitor Microcontroller opens the solenoid valve with a SET on GASEN and verifies the flow rate by monitoring the current through the flow control valve.

Referring to the HV/Flow Control Schematic (Figure C-4b), VGAS is an analog voltage for the mass flow rate and has a range of .5V to 6.2V. To enable the circuit, AR_EN must be SET causing U13-7 to go low.

The absolute pressure transducer (X2) measures the atmospheric pressure, plus the back pressure within the argon flow tubes when argon gas is flowing. This signal is referred to as PABS (TP4) and is calibrated for a specific voltage depending on the altitude where calibration occurs. Once calibrated, then PABS will automatically adjust to any change in altitude where the system may be placed into service. At sea level, PABS will be approximately 5.22V and at an altitude of one mile, PABS will measure about 4.13V.

Signal control needs to be defined at this time. As mentioned, the System 7500™ has two (2)

The differential pressure transducer (X1) has two hoses, or two input ports for argon hose connec-

6.6.2

6-14

Mass Flow Rate Regulation