Giraffe Infant Scale Service Manual Rev ZAA

Table of Contents 1/Functional Description 1.0 General...1-1 1.1 Scale Assembly...1-1 1.2 Load Cell Transducer...1-1 1.3 Cable and connector...1-1 1.4 Weighing and Interface Electronics...1-2 1.41 Differential Signal Amplification...1-2 1.42 Additional Amplification and Signal Filtering...1-2 1.43 Analog and Digital Conversion...1-3 1.44 DC Power Supplies...1-4 1.45 Microcomputer and Support Circuits...1-5 1.46 Interface to Giraffe Data Bus...1-6 1.5 SR and SC display...1-8 1.6 Specifications...1-9 2/Checkout Procedures 2.1 Mechanical check...2-1 2.2 Center weight check...2-1 2.3 Off center weight check...2-1 3/Maintenance and Calibration 3.1 Maintenance schedule...3-1 3.2 Service Tools...3-1 3.3 Calibration procedure...3-1 4/Troubleshooting 4.1 Error Codes...4-1 4.2 Troubleshooting Table...4-1 4.3 Service screen...4-3 4.4 Indicator lamp array check...4-3 5/Repair Procedures 5.1 Scale Top Frame Removal...5-1 5.2 Scale Top Frame Attachment...5-1 5.3 Circuit Board Removal...5-1 5.4 Circuit Board Replacement...5-1 5.5 Cable Assembly Removal...5-2 5.6 Cable Assembly Replacement- Plastic Frame Units...5-2 5.7 Cable Assembly Replacement- Metal Frame Units...5-2 5.8 Load Cell Removal...5-4 5.9 Load Cell Replacement...5-4 6/Illustrated Parts 6.1 Service Parts...6-1 6.2 Wiring Diagrams...6-3 Appendix A Additional Safety Information... A-1 i

Precautions CAUTIONS Only competent individuals trained in the repair of this type of equipment should attempt to service it as detailed in this manual. Always perform the checkout procedure after performing any type of repair and before placing the scale back in service.

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1/Functional Description (23G10RA instrument board) 1.0 General The Ohmeda Medical Giraffe® Infant Scale utilizes the latest developments in transducer technology and integrated circuits to provide a highly reliable and accurate weighing scale. This section describes the technical aspects of the Giraffe accessory infant scale. A schematic diagram and parts list is included within this manual. Please refer to it when reading the following technical description.

1.1 Scale Assembly Each scale assembly contains the following: 1.

Load cell transducers (4).

2.

Cable and connector.

3.

Weighing & interface electronics.

1.2 Load Cell Transducer The function of the load cell transducer is to convert the weight applied to the weighing platform into an electrical signal for further processing and subsequent transmission by the scale’s electronics. Four (4) special load cell transducers are contained within the scale assembly. A separate “coplanar fold back beam” is mounted under each of the four corners of the scale, between the top and bottom surfaces. These load cells are very sensitive and precise devices which produce a voltage output in direct proportion to the weight applied. This change is linear to within + 0.05%. Two dual strain gauges are mounted on each simple beam to measure tension and compression of the beam as weight is applied. The four gauges of each simple beam are wired in a Wheatstone bridge configuration. This transducer arrangement is “excited” (powered) with a regulated +10 volts D.C. from the scale electronic’s power supply. The “excitation” voltage is applied to the opposite corners of the bridge designated “+EXC” and “-EXC”. The signal output (“+SIG” and “-SIG”) is the total voltage that changes in proportion to the weight applied. This output is a very low level DC voltage (in the millivolt range at full scale capacity). Each load cell has a small circuit which contains various resistors which are selected to insure matching of the four load cells. Correction of the load cell’s output signal due to changes in temperature is also accomplished by compensating resistors on this circuit. The four load cells are further interconnected in parallel, by the scales instrument board, in order to “sum” the total weight applied to the scale platform.

1.3 Cable and Connector The scale is interconnected to the Giraffe by means of a seven-conductor (plus shield) cable and an eight circuit connector (one position not used). The cable shield is used to interconnect the load cell transducer beams and the shielding around the printed circuit assembly as an aid in protecting the scale from ESD (electrostatic discharge). Color coding of the lead wires is as follows: Red: Brown: Green: Orange:

+12V Power supply /System failure /Interrupt RS-485 communication line “A”

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1/Functional Description Yellow: Blue: Black:

RS-485 communication line “B” Reset Common or circuit ground

1.4 Weighing and Interface Electronics The electronic circuit board contained within the Giraffe accessory scale is used to process the signal from the load cell transducers of the weighing platform and provide an interface to the internal electronics bus of the Giraffe. Note that the scale shares the same data/power bus as do the various other modules of the system. The scale electronics consists of the following: 1.

Differential signal amplification.

2.

Additional amplification and signal filtering.

3.

Analog to Digital (A/D) converter & clock

4.

DC power supplies.

5.

Microcomputer and support circuitry.

6.

Interface to Giraffe data bus.

1.41 Differential Signal Amplification The weight dependent output signal produced by the load cell transducers in the scale platform is a “differential signal”, meaning it is the voltage difference between the “+ Signal” and “- Signal” leads. Integrated circuit U4, an instrumentation amplifier, is used to interface to this differential signal and amplify it. The four individual load cell transducers are parallel connected at connectors J4A, J4B, J4C, & J4D. This summed weight output signal is applied to the protection network consisting of diodes CR4/CR5/CR6/CR7. These diodes prevent destructive overvoltages caused by static discharges from damaging U4. A “guard trace” is also provided on the printed circuit assembly to help prevent leakage to the signal pins of the load cells. The guard trace is biased by resistors R15 and R16. A high frequency filter, formed by L1/L2/C9/C10, couples the weight signal to the input of U4. In U4 the differential signal is amplified by a factor of 100, and converted to a “ground-referenced” voltage for further processing. Capacitors C24/C16/C17 provide local bypassing of the power supplies used by instrumentation amplifier U4. Capacitor C18 furnishes compensation of U4 by reducing amplification at higher frequencies.

1.42 Additional Amplification and Signal Filtering Operational amplifier U5 is included to provide additional gain and signal filtering. U5, together with capacitors C14/ C15 and resistors R17/R18, forms an active low-pass filter. This helps to remove fluctuations in the weight signal caused by movement of the patient on the scale. U5, like U4, is “chopper-stabilized” to correct internal offset and drift errors. Resistor R24 is used to increase the gain of the amplifier stage in order to provide the required voltage output level. Resistor R22 biases the amplifier stage in a negative direction to increase dynamic range for scale operation; this helps remove any positive offset from the load cell transducers and also removes the weight of the scale’s top platform. The increased dynamic range allows more non-patient weight (“tare”, such as blankets and pillows) and patient weight to be applied to the scale before exceeding the input range of the A/D converter. An additional low-pass filter stage is furnished by resistor R34 and capacitor C23.

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1/Functional Description 1.43 Analog and Digital Conversion Integrated circuit U6 is the analog-to-digital converter. Included on this integrated circuit are auto-zero functions, auto-polarity, and the digital and analog functions necessary to perform dual slope integration conversion to 20,000 counts (4 1/2 digits). The weight signal voltage is applied to the analog input (pin 10) of U6. A reference voltage for the conversion is applied to pin 2 of U6. The reference voltage, nominally 1 Volt, is derived from the load cell transducer excitation voltage (+10V), by the divider network consisting of resistors R29 & R30. The system clock, applied at pin 22 of U6, is used to precisely time and control the phases of the dual slope conversion process. The system clock is generated by microcomputer U10 from its port P1.0, and consists of a square wave of approximately 160khz. The following diagram details the operation:

PHASE 1 AUTO ZERO

PHASE 2 SIGNAL INTEGRATE

PHASE 3 REFERENCE INTEGRATE

LARGE

SMALL 10,001 CLOCK PULSES

10,000 CLOCK PULSES

UP TO 20,000 CLOCK PULSES

1.43.1 Phase 1, Auto Zero During auto zero, the errors in the analog components (offset voltages of buffers, comparators, etc.) will be automatically nulled out. This is performed by internal logic that disconnects the input pins (9 & 10) from the applied analog signal, connects them to ground, then closes an internal feedback loop such that offset error information is stored in the “auto zero” capacitor, C21. Also during this phase, “reference capacitor” C22 is charged to the voltage present on “Vref” (pin 2 of U6). 1.43.2 Phase 2, Signal Intergrate The input signal is reconnected and then integrated for exactly 10,000 clock pulses. On completion of the integration period, the voltage V-int is directly proportional to the input voltage, corresponding to the weight applied to the scale. Capacitor C20 is the integration capacitor, with resistor R32 setting the integration current. At the end of this phase the input signal polarity is determined. 1.43.3 Phase 3, Reference Integrate, Signal De-intergrate The input to the integrator is switched from the input signal to reference capacitor C22. Internal switches connect capacitor C22 to the integrator input so that its polarity is opposite that of the previously applied input signal. This causes the integrator to discharge back towards zero. The number of clock pulses counted between the beginning of this cycle and the time when the integrator output passes through zero is a digital measure of the magnitude of the input signal. This count is stored in an internal latch on U6 for output to the microcomputer. 1.43.4 Zero Integrator Phase One minor additional phase is included to insure that the integration capacitor C20 is fully discharged to zero volts. This typically lasts 100-200 counts.

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1/Functional Description 1.44 DC Power Supplies Four separate dc power supply voltages are provided on the circuit board for powering the various sections of the electronics. These include +10V (“+Exc”) for load cell excitation, +5V (VAA) for analog circuits, +5V (VCC) for digital circuits, and -5V for analog circuits. Use of two separate +5V supplies prevents digital noise from entering the sensitive analog circuits. The two +5V power supplies and the +10V supply are obtained by reducing & regulating the +12V from the Giraffe’s data/power bus. While +5V is available directly from the Giraffe’s data/power bus, it is generated locally to simplify the connecting cable and interface. An additional circuit consisting of Q1 and related components is included to provide a gradual turn-on to the scales power supply in order to eliminate problems with “hot-plugging”. See section 1.46 for additional details 1.44.1 +5V Supplies Voltage regulators VR2 and VR3 render regulated sources of +5 Volts D.C. for operation of the analog (VAA) and digital (VCC) circuits, respectively. As mentioned earlier use of two separate +5V regulators helps to prevent noisy digital signals from entering the sensitive analog circuits. VR2 and VR3 are three-terminal regulators that are very stable with load & temperature and provide internal current limiting. Capacitors C3 and C8 are used to insure regulator stability. Capacitors C37 & C38 provide high-frequency bypassing of the respective power supply. An indicator LED, marked “+5V”, is provided for troubleshooting purposes and lights when the +5 volt supplies are operating. Current limiting for the LED is provided by resistors R67 and R68. Since the current is summed from the two +5 volt supplies to light the LED, the LED will be noticeably dimmer than the others if one of the two +5 volt supplies is not working. 1.44.2 +10V Supply VR1 is an integrated circuit voltage regulator that provides a stable source of +10V (“+EXC”) for load cell transducer excitation and amplifiers U4/U5. VR1 reduces the +12V input to +10V and maintains a steady output with load current and temperature fluctuations. VR1 is actually a +5V fixed output regulator which has its common terminal connected to the VAA (+5V) power supply. This “stacks” the VR1 +5V regulator on top of the +5V VR2 regulator in order to provide a regulated source of +10V. Additional components used include capacitor C27 to stabilize the regulator, capacitor C26 to contribute high frequency filtering, & schottky diode CR2 to insure the “stacked” regulator configuration initializes properly. An indicator LED, marked “+10”, is utilized for troubleshooting purposes and lights when the +10 volt supply is operating. Current limiting for the LED is provided by resistor R69. 1.44.3 -5V Supply Integrated circuit U2 is used to convert +5 Volts D.C. to -5 Volts D.C. for use in the analog circuits. It contains an internal oscillator (operating at approximately 10 KHz) and a series of switches. During one half of the cycle capacitor C4 is connected between +5 Volts and ground. During the other half cycle capacitor C4 is reconnected between ground and pin 5, with its polarity such that the negative terminal of C4 is connected to pin 5 of U2. C4’s charge is then transferred into capacitor C5, which filters the voltage, furnishing the -5 Volt D.C. output.

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1/Functional Description 1.45 Microcomputer and Support Circuits A microcomputer is employed to additionally process the data supplied by the A/D converter and execute the commands and responses from the Giraffe system. This microcomputer system consists of U10, a microcomputer; U9, a nonvolatile memory which remembers calibration and use data; and U11, a device to generate reset conditions for the microcomputer. During operation of the scale the microcomputer continually receives the weight readings from the A/D converter. This data is received in a “multiplexed” format (one digit at a time) from the output of the A/D converter (microcomputer port lines P1.1 through P1.7). The microcomputer also continually monitors the Giraffe data bus and listens for commands relevant to the scale. After processing the A/D data the microcomputer assembles it for subsequent transfer to the Giraffe when requested. U10 is a complete microcomputer, containing a software program stored in read-only memory, read/write memory for temporary storage of program variables, an arithmetic logic unit, input/output and other control lines, etc. U10 also contains an internal UART (universal asynchronous receiver transmitter), which allows serial communication between it and the Giraffe. Crystal XTAL1 and capacitors C29/C30 form the clock oscillator which controls the internal timing of the microcomputer. 1.45.1 Nonvolatile Memory The internal memory of microcomputer U10 does not retain data when the power is switched off. Because lasting data retention is required for scale weight calibration integrated circuit U9 is included. This device, called an “electrically erasable programmable read only memory”, or “EEPROM” will store information for periods of up to 100 years. Information needed to be stored to or retrieved from U9 is sent in serial form using the lines SCL (serial clock) and SDA (serial data). These are controlled by microcomputer U10. A data bit (a high or low level) is sent and received on SDA when the SCL line provides a pulse. Resistors R54/R55 are provided as pull-ups on the SCL/SDA lines to insure the data and clock pulses are properly shaped. 1.45.2 Reset Generation In order for microcomputer U10 to properly execute its software instructions it must be initialized to the start of the program when power is first turned on. “Reset” pin 9 of U10 will accomplish this when it is set “high”. U11 is a “watchdog timer” included to provide the reset when needed. The +5V VCC supply is monitored by the device and the reset line of U10 is set when VCC is insufficient to guarantee operation of the microcomputer. Once the proper minimum level of VCC is attained (approximately 4.75 V) the reset line is set low and the microcomputer is allowed to run its software program. Additionally an on-board timer of U11 must be reset periodically by pulsing its input pin, “WDI”; this is done by microcomputer U10 using port pin P3.6. Failure of the microcomputer to reset this timer, caused by an error in its operation, will cause U11’s watchdog timer to time out. This sets line “/WDO” (watchdog output) low, and subsequently pulls the “/MR” (master reset) line low through small signal schottky diode CR20. This initializes a reset pulse and restarts microcomputer U10. Diode CR22 is included to couple an external reset pulse from the Giraffe’s data bus (see section 1.46.5). An additional “data line time delay” is fabricated using the remaining part of U11. See section 1.46.1 for additional details.

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1/Functional Description 1.46 Interface to Giraffe Data Bus Since the scale plugs into the existing Giraffe electronics data bus, it must conform to the specifications of that data bus. Circuitry is also included on each line to provide “hot-plug” capability, which allows the scale to be plugged or unplugged from the Giraffe while the power is on and the Giraffe is operating. Signals to and from the scale include the following: Common ground:

The common return for all the circuitry.

+12V DC Power:

Power source used by the scale for all its circuitry. This voltage is the source for the scale’s own internal voltage regulators and converters.

/System failure:

This is an output to the scale and other modules from the Giraffe indicating that the system has encountered a failure and that each module should take appropriate action. The /System failure line, which normally idles at “high” (+5V), is pulled “low” by the Giraffe to indicate a problem.

/Interrupt:

An input to the Giraffe signaling that a module(s) is requesting attention. Normally idling at “high” (+5V), it is pulled “low” (towards “0V”) by the module making the request. Upon receiving the /Interrupt signal the Giraffe will poll each module to determine if it was the one that required attention. Once the interrupting module is queried, it will release the /Interrupt line.

Reset:

A signal to the scale and any other modules to return to their initial “start-up” state. A reset pulse is provided on power-up of the Giraffe.

RS-485A, RS-485B: A pair of lines used to provide communication between the Giraffe and all modules. Serial data is transferred over these lines. The use of a differential pair of lines provides high noise immunity and therefore excellent signal integrity. 1.46.1 Data Line Time Delay A time delay is provided in the scale’s electronics which prevents any of the scale’s three output lines, /INT, RS-485A, RS-485B, from activating during “hot-plugging” and corrupting the operation of the Giraffe. The term “hot-plugging” refers to plugging and unplugging the scale from the Giraffe while it is powered on and functioning. These output lines are kept disconnected from the Giraffe by the normally open contacts of relays RLY1 and RLY2. The parallel connected coils of the relays are energized by mosfet transistor Q22. Zener diode CR21 is provided to protect transistor Q22 from inductive transients caused by the two relays switching off. Resistor R71 reduces the power dissipation of the relay coils. A time delay is furnished by the network consisting of resistors R60, R61, R70, and capacitor C61. This time delay is on the order of several seconds, and is connected to the “PFI” line of U11. When the voltage on the C61 line reaches approximately +1.25 volts, watchdog timer U11 will set the /PFO line high, energizing Q22, and therefore switching the relays. Transistor Q20 is used to discharge the capacitor C61 when a reset occurs and therefore restart the time constant. Also upon reset, microcomputer U10 sets its port lines “high”. Transistor Q21, which is connected to port pin P3.7, will keep C61 discharged until U10’s software sets port P3.7 “low”. This allows U10 to further delay the data line connection until it is ready. An extra set of contacts on relay RLY1 is used to tell U10 through port P2.3 that the relays have closed. 1.46.2 +12 Volt Power Interface Power is applied to the VR1 / VR2 / VR3 voltage regulator array by use of mosfet transistor Q1. Q1, a P-channel

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1/Functional Description device, is included to provided a gradual “soft-start” of the scale’s power supply. This is done to insure that hotplugging the scale will not cause a surge on the power supply of the Giraffe and upset its operation. Capacitor C1 is connected across the gate and source of Q1. A time delay circuit is formed from C1 and resistor R2. Upon connection of the scale to the Giraffe, Q1 is initially kept off by a discharged C1. As C1 charges through R2 it gradually forward biases the gate of Q1, turning it on slowly and allowing current to gently flow into the remainder of the scale’s electronics. Diode CR1 and resistor R1 provide a rapid discharge of C1 so that momentary unplugging of the scale resets the soft-start time delay. Transient suppressor diode TS1 is included to protect the scale power supply from “ESD” (electrostatic discharge), momentary overvoltage, or reversed polarity connection. 1.46.3 /System Failure Interface A “low” signal on the /SYSTEM FAILURE (“/sysfail”) line tells the scale to shutdown. The scale’s /sysfail line is normally biased low by resistor R63; the Giraffe pulls this line up towards +5 volts under normal conditions. If the line becomes disconnected, or the Giraffe senses a serious problem, the line will go “low” and cause the scale’s software to shutdown. The “/sysfail” signal is connected to the network of resistor R62 and capacitor C6 to provide current limiting, ESD protection, and noise filtering. Integrated circuit U21 provides a pair of inverters that shape and buffer the signal before applying it port pin P3.2 of microcomputer U10. An indicator LED (light-emitting diode), marked “/SFL”, is also attached to the buffered line to help in troubleshooting, and lights when a system failure is occurring. Current limiting for the LED is provided by one resistor of network RN1. 1.46.4 /Interrupt Interface An “interrupt” line is used by all the modules to signal the Giraffe that they need attention. This line is normally biased “high” by the Giraffe. It is pulled “low” by one or more of the modules. The scale’s interrupt line, “/INT”, is isolated upon hot-plugging or power-up through relay RLY1 (see section 1.46.1). When microcomputer U10 requests attention from the Giraffe, it sets output port P2.5 “low”. Port P2.5 is buffered by two inverters from U21 then applied through schottky diode CR25 and relay RLY1 to connect to the Giraffe’s “/INT” line. Resistor R64 is included for current limiting. An indicator LED, marked “/INT”, is utilized for troubleshooting purposes and lights when the “/INT” line is low, indicating the scale is requesting attention. Current limiting for the LED is provided by one resistor of network RN1. 1.46.5 Reset Interface While the scale contains its own circuitry for resetting on power-up or other conditions, the Giraffe also provides a line labeled “RESET” to force an initialization of all modules. The “RESET” signal is connected to the network consisting of resistor R65 and capacitor C7 to provide current limiting, ESD protection, and noise filtering. A “pulldown” resistor, R66, is included to bias the reset signal so it is normally “low”. Integrated circuit U21 provides an inverter to shape and buffer the signal before applying it to watchdog timer/reset generator U11 through small signal schottky diode CR22 (see section 1.45.2). An indicator LED, marked “RST”, is utilized for troubleshooting purposes and lights when the “RESET” line is high, indicating the scale and other modules are being forced to reset by the Giraffe. Current limiting for the LED is provided by one resistor of network RN1. 1.46.6 RS-485 Communications Interface Communication between the scale and the Giraffe uses a format known as “RS-485”. This technique utilizes a differential voltage between two lines, labeled “A” and “B”. The data is transmitted as a serial string of “0’s” and

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1/Functional Description “1’s”, and is represented as a voltage on the A and B lines with A > B or B < A. Use of this differential voltage approach provides high noise immunity and signal integrity, since common mode interference is greatly rejected. Use of the RS-485 format allows multiple modules and the Giraffe to share the same pair of communication lines by taking turns, much like a telephone “party line”. Each module has a unique address used to identify it, and the Giraffe controls all communication by acting as the “master”. The data transfer between the Giraffe and any module also includes encoding for the number of digital bytes and a checksum, so that errors in communication can be readily identified. Communication takes place in “half-duplex” mode, which means receiving and transmitting must occur alternately. Communication occurs at a rate of 19,200 baud, producing a “0” or “1” pulse duration of 52 microseconds. U20 is an integrated circuit specifically designed to act as an RS-485 interface. It contains the necessary transmit and receive drivers to couple the scale’s microcomputer internal UART to the Giraffe’s RS-485 communication bus. Microcomputer U10 port pin P2.4 controls the transmit/receive function of the U20 interface through one of U21’s inverters. Data from the Giraffe is routed to microcomputer U10’s receive line, port P3.0, also known as “RXD”. Data to the Giraffe initiates from microcomputer U10’s transmit line, port P3.1, also known as “TXD”. Note that both the “A” and “B” lines are linked to the U20 interface circuit by relay “RLY2”. This relay disconnects these lines from the Giraffe during “hot-plugging” (see section 1.46.1) so as to prevent disruption of data communication between the Giraffe and various other modules. A pair of indicator LED lamps, marked “XMT” and “RCV”, are supplied for troubleshooting purposes and light when communication is taking place between the scale and the Giraffe. Correct operation will consist of a short blink from the “RCV” lamp, indicating the scale has received a query from the Giraffe, followed by a short blink from the “XMT” lamp, verifying the scale’s response. Note that because of the complex addressing involved on the RS-485 data bus, the indicator lamps provide a simulated transmit and receive indication of the scale’s data bus activity. The lamps are actually driven by microcomputer U10 as opposed to directly monitoring the data bus. Current limiting for the LED lamps is provided by two resistors of network RN1.

1.5 SR and SC display Two displays of internal scale operation are provided in the service menu. These are labeled “SR” and “SC”. Both pertain to values from the scale’s A/D (analog to digital) converter, which are in turn related to the weight applied to the top deck of the scale. Note that the scale must be connected to the OmniBed before entering the service menu to obtain the SC and SR displays. SR: Scale counts Raw. This is the actual digital, converted weight number received from scale’s A/D converter without any further processing. It can be thought of as the “hardware” value representing the weight applied to the scale. Each count of this value represents approximately 100 uVolts (0.0001V) DC applied to the input of the scale’s A/D converter. The range of displayed value is from -20,000 to +20000, corresponding to a voltage input applied to the A/D converter of -2.0000 Vdc to +2.0000 Vdc. In terms of weight applied to the scale, each count typically represents approximately 1.1 grams. Note that this value will vary with tolerances of the transducers and electronics, and could range from 0.85 gram to 1.20 gram per count. Calibration of the scale converts this count to an exact weight representation. The value of SR displayed without a weight, insert, and mattress will vary greatly, again due to the tolerance of the transducers and electronics. Values may range from –5000 to +3000 under this condition. Provided the scale’s top deck is stable, the value displayed should not momentarily fluctuate more than five counts total. SC: Scale counts Calibrated. This is the weight value after processing from the scale’s internal microcomputer. It can be thought of as the “software” value representing the weight applied to the scale. On a properly calibrated scale, each count of this value represents exactly 1 gram of weight . The range of possible displayed values is from 0 to 40000; offsets and correction factors will limit this to a smaller range.

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1/Functional Description To observe scale operation using the “SC” display, note the displayed value without weight. Add a test weight to the platform. The new value should closely equal the previous number plus 1 count for every gram of weight applied. As an example, if the no weight SC value is 20000, adding a 5000 gram (5 kilogram) test weight should produce an SC value of approximately “25000”. The value of SC displayed without a weight, insert, and mattress will vary greatly, due to the tolerance of the transducers and electronics. Values may range from 16000 to 23000 under this condition. Provided the scale’s top deck is stable, the value displayed should not momentarily fluctuate more than four counts total.

1.6 Specifications Functional range

300 gm to 8 kg

Accuracy

+/- 10 gm

Resolution

10 gm (factory setting) or 5 gm

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Notes

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2/Checkout Procedures The scale can be calibrated using a Class F calibration weight between 1 kilogram and 8 kilograms (accuracy of 0.01%). It is recommended to perform weight testing of the scale with a 5 kilogram (5000 gram) certified test weight. This weight is available as Ohmeda part number 6600-0209-800.

2.1 Mechanical check 1

Examine the scale connector cord for damage. Examine the LEMO connector to make sure it is tightly assembled. Check for bent pins. If the any of the parts are damaged replace them.

2. Examine the scale for obvious signs of damage.

2.2 Center weight check For best test accuracy enter the service screen and set the scale resolution, “Scale R”, to 5 grams, then shut off the unit and power it back up to enter normal weighing mode. Place a known weight in the center of the mattress and perform a weigh cycle. The displayed weight should be the known weight +/- 10 grams.

2.3 Off center weight check For best test accuracy enter the service screen and set the scale resolution, “Scale R”, to 5 grams, then shut off the unit and power it back up to enter normal weighing mode. Place a known test weight 10 cm (4”) from the center of the mattress in 4 positons 90 degrees from each other (for example- toward each corner of the matress) and check the reading at each position. Resulting weight readings should be within +/- 10 grams of previously obtained center weight reading.

Important: If the scale fails the weight checks, calibrate it according the procedure in section 3 and then perform the weight checks again.

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Notes

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3/Maintenance and Calibration 3.1 Maintenance Schedule Annual

Perform checkout procedures in section 2. If the scales fails the weight check, perform the calibration procedure below.

3.2 Service Tools Note: The scale can be calibrated using a Class F calibration weight between 1 kilogram and 8 kilograms (accuracy of 0.01%). A 5 kilogram (5000 gram) certified test weight is available from Ohmeda Medical (part number 6600-0209-800).

3.3 Scale Calibration 1.

Place the test weight on the center of the bed.

2.

Hold the override key (>37) while powering up to enter the service screen.

3.

On the second service screen, select Cal Scale.

4.

Remove the weight and push the knob at the screen prompt “REMOVE THE WEIGHT AND PUSH KNOB”. The screen will prompt “INITIALIZING...” for a few seconds.

5.

Replace the weight and push the knob at the screen prompt “PLACE TEST WEIGHT AND PUSH KNOB”. The screen will prompt “MEASURING ...” for a few seconds

6.

When the screen prompts “ENTER TEST WEIGHT” Dial in the test weight to the nearest gram. Press the knob to enter. The screen will prompt “CALCULATING.” for a few seconds.

7.

When the screen prompts: SAVE AND EXIT EXIT ONLY RESTORE DEFAULT Select and enter “SAVE AND EXIT”

8.

Turn off the power to exit the service mode.

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Notes

3-2

4/Troubleshooting 4.1 Error Codes Error Code No.

Meaning

Possible Causes

Actions

Scale Failure “1”

Microcomputer random access memory failed test on power up.

Faulty RAM memory in microcomputer U10.

Replace microcomputer U10 on printed circuit board of scale.

Scale Failure “2”

Microcomputer program memory failed checksum test on power up.

Faulty flash EPROM memory in Replace microcomputer U10 on microcomputer U10. printed circuit board of scale.

Scale Failure “3”

No output data from A/D converter.

A/D converter not running or defective.

Replace printed circuit board assembly of scale.

Scale Failure “4”

Output signal from A/D converter is over range.

Platform overloaded. Defective loadcell(s) or printed circuit board.

Remove any items from platform. Check load cells for high offset by checking “SR” value on service screen (see section 1.5). To determine specific load cell remove scale top and PC shield cover and disconnect/reconnect load cells (J1, J2, J3 & J4) one at a time until SR value returns to typical.

Scale Failure “5”

EEPROM memory has failed.

Problem with U9 EEPROM IC.

Replace printed circuit board assembly of scale.

Scale Failure “6”

Field Calibration data has been damaged.

Problem with U9 EEPROM IC.

Perform scale calibration. If problem persists replace printed circuit board.

Scale Failure “7”

Factory Calibration data has Problem with U9 EEPROM IC. been damaged.

Replace printed circuit board assembly of scale.

4.2 Troubleshooting Table Problem

Possible Cause

Action

Scale Icon does not appear on Giraffe control panel

Scale not plugged in.

Plug scale into Giraffe receptacle.

Defective cable.

Check cable continuity. Repair or replace cable.

Defective printed circuit board.

Replace printed circuit board.

Scale receptacle on Giraffe defective.

Replace scale receptacle on Giraffe.

Defective cable

Repair or replace cable.

Defective printed circuit board.

Replace printed circuit board.

Scale connector not making good contact with Giraffe.

Check that connector is fully inserted. Check that LEMO connector is tightly assembled. Check for bent pins.

Defective cable.

Check cable continuity. Repair or replace cable.

Defective printed circuit board.

Replace printed circuit board.

Scale receptacle on Giraffe defective.

Replace scale receptacle on Giraffe.

Scale causes Giraffe malfunction

Scale icon disappears/reappears on control panel. Scale makes repeated clicking noise.

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4/Troubleshooting Problem

Possible Cause

Action

Scale never completes weighing cycle

External mechanical interference.

Check for interference with scale top weighing (patient tubing, wires, severe vibration). Place scale outside of Giraffe and check operation.

Internal mechanical interference.

Remove scale top frame and check for interference between top frame, load cells and wiring.

Defective load cell.

Check output of scale using service screen. Check “SR” (Scale counts Raw) display. Number displayed should not fluctuate by more than 4 counts when at rest. If excessive fluctuation is noted disconnect load cells one at a time to isolate; replace individual defective load cell.

Defective printed circuit board.

Replace printed circuit board.

Mechanical interference

Perform off center weight check to determine corner weight readings. Examine defective corner and correct interference.

Patients weights inconsistent, erratic

Defective load cell

Perform checkout procedure. If it fails, perform load cell check below. Replace load cell as needed.

Defective printed circuit board.

Replace printed circuit board.

Load Cell Check To test for a defective loadcell start by placing the test weight place in the center of the platform and perform a weighing. Then place the center of test weight directly over each loadcell and perform a “Reweigh”. (The center of the loadcell is where the mounting screw is located on the top platform; 4 places). All four readings should be similar. If not, the weight reading that’s off the most is likely the defective load cell.    Note: All four loadcell input connectors (J1, J2, J3 & J4) are parallel wired so load cell connection positions are interchangeable. Load cell resistance readings are as follows: Excitation: green/black wires: Signal: red/white wires:

1000- 1300 ohms 975 - 1025 ohms

Note that the change in load cell resistance due to applied load is generally not measurable due to the bridge configuration and the very small values involved.

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