E-sCAixxx Respiratory Modules Technical Manual May 2014

Table of contents

Table of contents 1

About this manual 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

2

2.3

3

5

24

Software update... 24

Maintenance and checkout 5.1

22

Compatibility... 22 Installation... 22 3.2.1 Installing the Respiratory Module in the anesthesia system... 22 3.2.2 Installing ETC option for the Aisys CS2 anesthesia system... 23 3.2.3 Installation checkout procedure... 23

Configuration 4.1

3

Introduction... 3 Measurement principle... 4 2.2.1 CO2, N2O, and agent measurement... 4 2.2.2 O2 measurement... 6 2.2.3 Patient spirometry... 6 2.2.4 Gas exchange measurement... 8 2.2.5 ETC mode and fresh gas sample check... 9 Main components... 9 2.3.1 Controls and connectors... 9 2.3.2 Gas sampling system... 10 2.3.3 MiniTPX measuring unit... 16 2.3.4 MiniOM oxygen sensor... 16 2.3.5 MiniPVX measuring unit... 18 2.3.6 Gas exchange... 19 2.3.7 CPU board... 19 2.3.8 MiniOM board... 20 2.3.9 MiniPVX board... 20 2.3.10 Main Component Interactions... 20

Hardware installation 3.1 3.2

4

Intended use of the manual... 1 Intended audience of the manual... 1 Conventions used in this manual... 1 Illustrations and names... 1 Related documents... 1 Trademarks... 2 1.6.1 Third party trademarks... 2 Responsibility of the manufacturer... 2 Product availability... 2

Product overview 2.1 2.2

1

25

Replacement of planned maintenance parts... 26 5.1.1 Required parts... 26

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5.2 5.3

6

Calibration and adjustments 6.1 6.2 6.3

7

7.3 7.4 7.5

8.2

42

Visual inspection... 42 Troubleshooting checklist... 42 7.2.1 Gas sampling system troubleshooting... 43 7.2.2 MiniOM Measuring unit troubleshooting... 43 7.2.3 MiniTPX Measuring unit troubleshooting... 43 7.2.4 MiniPVX Measuring unit troubleshooting... 43 7.2.5 CPU board troubleshooting... 43 Service Interface... 44 Messages... 44 7.4.1 Gas measurements... 44 7.4.2 Spirometry... 47 Troubleshooting charts... 48 7.5.1 CO2 measurement... 48 7.5.2 Patient spirometry... 48

Disassembly and reassembly 8.1

34

Sample Flow Rate Adjustment... 34 6.1.1 Calibration setup... 34 6.1.2 Sample Flow Rate Adjustment... 34 Gas Calibration... 36 6.2.1 Calibration setup... 36 6.2.2 Procedure... 37 Spirometry Calibration... 39 6.3.1 Calibration setup... 39 6.3.2 Calibration check... 40 6.3.3 Flow calibration... 40

Troubleshooting 7.1 7.2

8

5.1.2 Planned Maintenance Kits... 26 5.1.3 Replacement procedures... 26 Visual inspections... 28 Functional check... 28 5.3.1 Test setup... 28 5.3.2 Procedure... 29 5.3.3 Test completion... 33

50

Disassembly guidelines... 50 8.1.1 Serviceable parts... 50 8.1.2 Service limitations... 50 8.1.3 ESD precautions... 51 8.1.4 Protection from dust... 51 8.1.5 Before disassembly... 52 8.1.6 Required tools... 52 Disassembly and reassembly procedure... 52 8.2.1 Detaching the Front Cover... 53 8.2.2 Detaching the Module Casing... 54 8.2.3 Replacement of Planned Maintenance Parts... 55 8.2.4 Replacement of CO2 Absorber... 55 8.2.5 Detaching the Latch... 56

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8.2.6 Detaching the Front Chassis Unit... 57 8.2.7 Detaching the Main Flow Connector... 59 8.2.8 Detaching the Connector for Fresh Gas... 59 8.2.9 Detaching the PVX Unit... 60 8.2.10 Detaching the Pump... 61 8.2.11 Detaching the OM holder... 62

9

Service parts 9.1 9.2

63

Ordering parts... 63 9.1.1 Planned Maintenance Kits... 63 Spare parts... 64 9.2.1 Front covers... 66

Maintenance check form

69

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1

About this manual

1.1 Intended use of the manual This manual contains instructions necessary to install, maintain and service the device to the assembly level. Use it as a guide for installation, maintenance and repairs considered field repairable. Where necessary the manual identifies additional sources of relevant information and technical assistance. See the CARESCAPE Respiratory Modules user’s manual for the technical specifications, and supplies and accessories. 

See the user’s manual for the instructions necessary to operate the device safely in accordance with its function and intended use.

1.2 Intended audience of the manual This manual is intended for service representatives and technical personnel who install, maintain, troubleshoot, or repair this device.

1.3 Conventions used in this manual Within this manual, special styles and formats are used to distinguish between terms viewed on screen, a button you must press, or a list of menu commands you must select:

•

For technical documentation purposes, the abbreviation GE is used for the legal entity names, GE Medical Systems Information Technologies Inc. and GE Healthcare Finland Oy.

•

Names of hardware keys on the equipment, keypad, remote control, and modules are written in bold typeface: Start Cancel.

• • •

Menu items are written in bold italic typeface: Monitor Setup.

• •

The word “select” means choosing and confirming.

•

Note statements provide application tips or other useful information.

Emphasized text is in italic typeface. Menu options or control settings selected consecutively are separated by the > symbol: Procedures > Cardiac Output. Messages (alarm messages, informative messages) displayed on the screen are written in bold italic typeface: Learning.

1.4 Illustrations and names This manual uses illustrations as examples only. Illustrations in this manual may not necessarily reflect all system settings, features, configurations, or displayed data.

1.5 Related documents 

Aisys CS2 Anesthesia Machine Technical Reference Manual



Aisys CS2 User’s Reference Manual



Aisys CS2 Et Control Addendum

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

Aisys CS2 Et Control Option



Avance CS2 documentation



CARESCAPE Respiratory Modules User’s Manual



the patient monitor’s user’s manual



the patient monitor’s supplemental information manual



CARESCAPE Modular Monitors Software Installation Instructions

NOTE: The referred documents above are subject to change without notice. Please contact your local sales or service representative for possible updates.

1.6 Trademarks Listed below are GE Medical Systems Information Technologies, Inc. and GE Healthcare Finland Oy trademarks. All other product and company names contained herein are the property of their respective owners. GE, GE Monogram, and CARESCAPE are trademarks of General Electric Company. D-lite is a trademark of GE Healthcare Finland Oy.

1.6.1 Third party trademarks All other product and company names are the property of their respective owners.

1.7 Responsibility of the manufacturer GE is responsible for the effects on safety, reliability, and performance of the equipment only if:

•

Assembly operations, extensions, readjustments, modifications, servicing, or repairs are carried out by authorized service personnel.

•

The electrical installation of the relevant room complies with the requirements of the appropriate regulations.

• •

The equipment is used in accordance with the instructions for use. The equipment is installed, maintained and serviced in accordance with the instructions provided in the related technical manuals.

1.8 Product availability Some of the products mentioned in this manual may not be available in all countries. Please consult your local representative for the availability.

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2

Product overview

2.1 Introduction This document provides information for the maintenance and service of the CARESCAPE Respiratory Modules E-sCAiOVE, E-sCAiOE, E-sCAiOVX, E-sCAiOV, E-sCAiO. The CARESCAPE Respiratory modules are single width plug-in modules. The CARESCAPE Respiratory modules provide airway and respiratory measurements. The modules with the ETC option also support End Tidal Control (ETC mode) function in Aisys CS2 anesthesia system. Letters in the module name stand for: C = CO2 and N2O, O = patient O2, V = patient spirometry, X = gas exchange, A = anesthetic agents, i = agent identification, and E = ETC mode

Options for CARESCAPE Respiratory modules Module

Parameters / measurements CO2

N2O

O2

Anesthetic Agent ID agents

Spirometry

ETC

E-sCAiOVE

X

X

X

X

X

X

X

E-sCAiOE

X

X

X

X

X

E-sCAiOVX

X

X

X

X

X

X

E-sCAiOV

X

X

X

X

X

X

E-sCAiO

X

X

X

X

X

Gas exchange

X X

X

NOTE: Anesthetic agents and N2O values are not displayed with ICU and ED software packages, but when present in the module they are calculated for compensation of CO2 and O2.

Figure 1

Airway gases measurement setup

(1)

CARESCAPE Respiratory Module

(2)

Gas sample, gas sampling line connector on the water trap

(3)

Gas sampling line

(4)

Gas sampling line connector on the airway adapter; place the connector upwards

(5)

Airway adapter with sampling line connector

(6)

Heat and moisture exchanger with filter (HMEF) (optional)

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(7)

Connector for Fresh Gas in ETC mode

(8)

Connector for the gas exhaust line (sampling gas out)

2.2 Measurement principle 2.2.1 CO2, N2O, and agent measurement MiniTPX is a side stream gas analyzer, measuring real time concentrations of CO2, N2O, and anesthetic agents (Halothane, Enflurane, Isoflurane, Desflurane, and Sevoflurane).

Figure 2

MiniTPX sensor principle

Anesthetic agents or mixtures of two anesthetic agents are automatically identified, and concentrations of the identified agents are measured. MiniTPX also detects mixtures of more than two agents and issues an alarm. MiniTPX is a non-dispersive infrared analyzer, measuring absorption of the gas sample at seven infrared wavelengths, which are selected using optical narrow band filters. The infrared radiation detectors are thermopiles. Concentrations of CO2 and N2O are calculated from absorption measured at 3-5 m.

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Figure 3

Absorbance of N2O and CO2

Identification of anesthetic agents and calculation of their concentrations is performed by measuring absorptions at five wavelengths in the 8-9 m band and solving the concentrations from a set of equations.

Figure 4

Infrared absorbance of AAs

The measuring accuracy is achieved utilizing numerous software compensations. The compensation parameters are determined individually for each MiniTPX during the factory calibration.

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2.2.2 O2 measurement The differential oxygen measuring unit uses the paramagnetic principle in a pneumatic bridge configuration. The signal picked up with a differential pressure transducer unit is generated in a measuring cell with a strong magnetic field that is switched on and off at a main frequency of 164 Hz. The output signal is a DC voltage proportional to the O2 concentration difference between the gas to be measured and the air reference.

Figure 5

O2 measurement principle

2.2.3 Patient spirometry In mechanical ventilation, breaths are delivered to the patient by a ventilator with a proper tidal volume (TV), respiration rate (RR), and inspiration / expiration ratio in time (I:E) determined by the settings of the ventilator. The Patient Spirometry monitors patient ventilation.

The following volume parameters are displayed:    

Expiratory and inspiratory tidal volume (TV) in ml Expiratory and inspiratory minute volume (MV) in l/min Expiratory spontaneous minute volume in l/min Inspiration/expiration ratio (I:E)

The following airway pressure parameters are displayed:     

Peak pressure (Ppeak) Mean airway pressure (Pmean); available only with ICU and ED software packages End inspiratory plateu pressure (Pplat) PEEPi, PEEPe; available only in with ICU and ED software packages Total positive end expiratory pressure (PEEPtot); available with OR and PACU software packages  Real time airway pressure waveform (Paw)  Static Positive End Expiratory Pressures (Static PEEPi and Static PEEPe); available with ICU and ED software packages  Static Plateau pressure (Static Pplat); available with ICU and ED software packages  Static Compliance (Static Compl); available with ICU and ED software packages PEEP, Ppeak, Pmean, and Pplat are measured by a pressure transducer on the MiniPVX board. Ambient pressure is used as a reference in measurement. The pressure measurement is made from the airway part that is closest to the patient between the patient circuit and intubation tube.

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PEEPi=intrinsic PEEP, PEEPtot-PEEPe Static pressure measurement maneuvers are automatically identified based on an increased zero flow period at the end of the inspiration or expiration. Static Compliance is calculated, if Static PEEP and Static Pplat measurements were made within a 2 minute period.

The following airway flow parameters are displayed:  Real time flow waveform (V')  Compliance (Compl)  Airway resistance (Raw)  Pressure volume loop  Flow volume loop The measurement is based on measuring the kinetic gas pressure and is performed using the Pitot effect. A pressure transducer is used to measure the Pitot pressure. The pressure signal obtained is linearized and corrected according to the density of the gas. Speed of flow is calculated from these pressure values and the TV value is then integrated. The MV value is calculated and averaged using TV and RR (respiratory rate) values.

D-lite Patient Spirometry uses specific sensors called D-lite+/D-lite and Pedi-lite+/Pedi-lite flow sensors. Different types of sensors are available: adult sensor for measuring adults and pediatric sensor for children. Both are available as reusable and disposable versions. D-lite and Pedi-lite adapters are designed to measure kinetic pressure by a two-sided Pitot tube. Velocity is calculated from pressure difference according to Bernoulli's equation. Flow is then determined using the calculated velocity.

(from Bernoulli's equation)

Formula 1

where: V’ = flow (l/min), v = velocity (m/s), A = cross area (m2), dP = pressure difference (cmH2O),  = density (kg/m3) Finally, the volume information is obtained by integrating the flow signal.

Compliance and airway resistance Compliance is calculated for each breath from the equation

Formula 2 Compliance describes how large a pressure difference is needed to deliver a certain amount of gas to the patient. The airway resistance, Raw, is calculated using an equation that describes the kinetics of the gas flow between the lungs and the D-lite. The equation states that the pressure at the D-lite can at any moment of the breath be approximated using the equation Formula 3

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where P(t), V’(t) and V(t) are the pressure, flow and volume measured at the D-lite at a time t, Raw is the airway resistance, Compl is the compliance and PEEPe+PEEPi is the total positive end expiratory pressure (PEEPtot).

2.2.4 Gas exchange measurement The gas exchange measurement uses the D-lite flow sensor and the gas sampling system. The basic data which is needed to obtain O2 consumption and CO2 production are volumes and concentrations. Concentrations have been corrected for delay and deformation during the transport of the gas sample in a sidestream gas measurement sensor. To obtain the amount of O2 consumed in ml/min, the amount which is exhaled is subtracted from the amount that is inhaled. To obtain the amount of CO2 produced in ml/min, the amount which is inhaled is subtracted from the amount that is exhaled. These amounts can be obtained by multiplying each measured volume piece (dv) by the corresponding gas concentration: Formula 4

and Formula 5

Using inspiratory and expiratory minute volumes MVi and MVe and volume-weighted inspiratory concentrations fi and fe, these equations can be rewritten as: Formula 6 Formula 7

To obtain results which are less sensitive to errors in volume measurements, the so-called Haldane transformation is used. This means taking advantage of the fact that the patient is not consuming nor producing nitrogen: the amount of nitrogen inhaled is equal to the amount  exhaled fiN2  MVi=feN2MVe. VO2 and VCO2 can then be written as: Formula 8 Formula 9

with fHald = (1-fiCO2 – fiO2 – fiN2O - fiAne1 – fiAne2) / (1-feCO2 – feO2 – feN2O - feAne1 – feAne2)

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2.2.5 ETC mode and fresh gas sample check ETC mode is an optional gas delivery mode on Aisys CS2 anesthesia system. In ETC mode the clinician sets the target end tidal O2 (EtO2) and target anesthetic agent (EtAA) values on the anesthesia system. The system receives the EtO2 and Et AA values from the Respiratory Module and adjusts the gas composition and total flow based on these values to maintain the set target values. ETC mode fresh gas sample check is a safety mechanism, which functions automatically when entering ETC mode. The ETC mode fresh gas sample check verifies the calibration of the Respiratory Module. This check runs approximately every three minutes while in ETC mode. Using the connector for fresh gas, a fresh gas sample is taken by the Respiratory Module from the anesthesia system instead of from the sample line at the breathing circuit. The fresh gas reading is compared to the expected fresh gas output on the anesthesia system. If the reading is out of limit the check fails and automatic exit of ETC mode occurs.

2.3 Main components The respiratory modules consist of:

• • • • •

Gas sampling system MiniTPX measuring unit MiniOM measuring unit MiniPVX measuring unit CPU board

2.3.1 Controls and connectors









Figure 6

Front of CARESCAPE Respiratory Module, E-sCAiOV, E-sCAiOVE and the back of the module

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(1)

D-fend Pro water trap

(2)

Gas sample, sampling line connector on the water trap

(3)

Water trap container

(4)

Connectors for Patient Spirometry

(5)

Gas exhaust, connector for the gas exhaust line (sampling gas out)

(6)

Connector for Fresh Gas in ETC mode

Module keys

Module

Description

Save Loop

E-sCAiOVE, E-sCAiOVX, E-sCAiOV

Save Loop saves a reference loop.

Change Loop

E-sCAiOVE, E-sCAiOVX, E-sCAiOV

Change Loop changes a pressure/volume loop to a flow/volume loop or vice versa.

Connector

Module

Description

D25 connector

all modules

Module bus connector

2.3.2 Gas sampling system The gas sampling system draws a 120ml/min sample from the patient's airway to the module. The sampling system also takes about 30ml/min flow of room air to the oxygen sensor. When the gas sensors are zeroed, room air is taken through the CO2-absorber to the gas sensors instead of the sampled gas from the patient's breathing. The gas sampling line is connected between the patient circuit and the Gas Sample port on the water trap. The water trap protects the sampling system and gas sensors from liquids and dust. The gas sampling system of the E-sCAiOE and E-sCAiOVE modules have an additional gas input port on the module’s front panel, as well as an extra valve for taking the fresh gas sample through this port during the fresh gas sample checks when the anesthesia machine is operating in the ETC mode. The diagram of the gas sampling system is shown in the figures below:

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Respiratory Modules E-sCAiOVE, E-sCAiOE, E-sCAiOVX, E-sCAiOV, E-sCAiO

Figure 7

Gas sampling system, E-sCAiOVE and E-sCAiOE (with ETC option)

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The sampling system has a self diagnostics that detects disturbances in the gas flow, reveals the most common reasons for disturbances, such as occluded sampling line or blocked gas exhaust line, and communicates relevant status messages to the patient monitor. The system is designed so that gas the sampled gas will not flow from the sampling line back to the patient circuit. The parts and connections of the sampling system are streamlined for minimal dead spaces and turbulences in gas flows. All gas inputs of the module have dust filters protecting the sampling system and gas sensors. The water trap acts as a dust filter for the sampled gas and the module should always have the water trap connected. NOTE: It is very important to prevent dust from entering the open gas connections during service operations.

D-fend Pro water trap The gas sampling line is connected to the input of the water trap where a special membrane passes gases and vapors but stops liquids. The gas flowing through the membrane continues via the main flow connector of the water trap to the module. The main flow is about 90% of the sample flow. Liquids stopped below the membrane are moved to the water container by a side flow that goes through the water container and the water separation membrane before entering the side flow connector of the water trap. Thus, the side flow also is free of liquids when it gets into the module. In the module, the side flow is connected directly to the pump input and it does not enter the gas sensors. NOTE: The water trap acts as a dust filter for the sampling system and gas sensors. Thus, the module should always have the water trap connected.

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Zero valve and CO2 absorber The zero valve is activated during gas sensor zeroing. In modules without ETC option room air is drawn through the CO2-absorber and the zero valve to the gas sensors, and the main flow of sample gas is stopped. In modules with ETC option, the air flows through the CO2 absorber, the fresh gas valve and the zero valve to the gas sensors. The zero gas comes to the sensors through the CO2-absorber that chemically absorbs CO2. The side flow of the water trap flows in the gas sampling line even during zeroing. During normal monitoring, the zero valve is not activated and the sampled gas gets through the zero valve to the gas sensors.

Figure 9

Absorber

Fresh gas valve During ETC mode fresh gas sample check the fresh gas valve and the zero valve are activated. A fresh gas sample is taken by the Respiratory Module from the anesthesia system. The fresh gas sample enters the module through the connector for fresh gas, and it flows through the fresh gas valve and the zero valve to the gas sensor. At the same time the main flow from the sample line at the breathing circuit is stopped. The side flow continues to flow to the pump without interruption. During normal monitoring the input of fresh gas to the module is stopped by the fresh gas valve.

Nafion tubes 1) The Nafion tube between the water trap and the zero valve equalizes the humidity of the sampled gas to ambient level. This will prevent calibration errors caused by the difference in humidities in the sampled breathing gas and the totally dry calibration gas. Another Nafion tube is used between the CO2 absorber and the zero valve to prevent condensation of water generated in the CO2 absorber as by-product of CO2-absorption.

Gas sensors After the zero valve, the gas flows through the MiniTPX sensor that measures the concentrations of all gases but oxygen. The oxygen concentration is measured in the MiniOM sensor that has two inputs. One input draws in a part of the main flow and the other draws in room air as reference gas for the O2 measurement.

Sample flow differential pressure transducer The module measures total flow at the input of the gas pump and reference flow at the OM reference line. The sample flow is the difference of these two flows.

1

Nafion is a registered trademark of Perma Pure Inc.

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Working pressure transducer The working pressure transducer measures absolute working pressure near the MiniTPX unit and MiniOM unit. It is used for messages: ‘Sample line blocked’, ‘Check D-fend’, ‘Replace D-fend’ and ‘Check sample gas out’.

Pneumatics The pneumatics contains the zero valve, the occlusion valve and the pneumatics block with tubing connections. The zero valve is activated during the zero level calibrations of gas sensors. The occlusion and zero valves are activated when the sampling line or water trap is occluded. With the activated valves, the gas pump generates maximal suction trough the “side flow” connector of the water trap, thus maximizing the transfer of liquids from the wet side of the water trap to the container. The pneumatics block contains a network of constrictions to divide the sampled gas in correct proportions to different parts in the module. The first branching takes place in the water trap where incoming flow is divided to the “main flow” and “side flow”. The second branching takes place before the MiniOM sensor. The pneumatics block also contains a pneumatic low pass filter between gas sensors and gas pump. The filter consists of constrictions (resistors) and volumes (capacitors) and it attenuates the pressure pulsation generated in the gas pump so that they do not disturb the operation of the gas sensors.

Gas pump unit The gas pump is a membrane pump run by a brushless DC-motor. The pump is adjusted so that the sample gas flow is kept close to its nominal value even when the flow resistances in the sampling line of water trap change. The pump is in a plastic enclosure to minimize the operating noise and mechanical vibration of the pump unit. A pneumatic damping chamber is integrated to enclosure to attenuate the pressure pulsation and noise conducted to the gas exhaust port.

Pressure measurements The four pressure sensors on the CPU board are used to measure ambient pressure, working pressure of the MiniTPX and MiniOM sensors and pressure of the reference gas flow to the MiniOM sensor.

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Sample flow control The gas flow in the sampling line is monitored by measuring the gas flow at the input of the gas pump and the reference flow to the oxygen sensor is estimated by measuring the pressure in the reference gas flow branch. The sample flow is calculated by subtracting the reference flow from the total gas flow. A control loop adjusts the rotation speed of the pump motor so that the gas flow is kept close to 120ml/min.

Gas sampling self-diagnostics The sample flow and the vacuum in the sampling system are used for continuous monitoring of the gas sampling system. The vacuum is calculated in real time as difference of the measured ambient and working pressures. The self-diagnostics of the gas sampling system sends the following status data to the patient monitor when specific triggering conditions are met: ‘Check water trap’, ‘Check sample gas out’, ‘Replace water trap’, ‘Sample line blocked’ and ‘Continuous blockage’. The gas pump is stopped when the 'Sample line blocked' has lasted for more than 1 minute. The module automatically restarts the pump to check whether the abnormal situation has been resolved so that normal gas sampling operation is possible. The gas pump repeats 1 minute full pump, 30 seconds pump off when the ‘Continuous blockage’ message is shown. 3QHXPDWLF %ORFN

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2.3.3 MiniTPX measuring unit The MiniTPX unit is a non-dispersive infrared analyzer, measuring the absorption of the gas sample at seven infrared wavelengths, which are selected using optical narrow band filters. The IR source is a micro-machined heating element with an integrated collimator. From the output of the source, the radiation is passed to a flow optimized measuring chamber. From the sample chamber, radiation goes via a specially designed beam splitter to two detector units, each with four thermopile detectors and integrated optical filters. The miniTPX measuring unit has two detector units for redundancy purposes. A more detailed description of the measuring principle can be found in section 2.2.1. CO2, N2O, and agent measurement. Each detector unit also measures the unit's temperature. The module CPU uses it for further processing and temperature compensation of the measured raw signals. The miniTPX unit includes an amplifier board with the following functions:

• •

On-board 5V regulator and 2.5V reference source.

• •

PWM controlled power for the IR source.

Preamplifiers for the eight thermopile detectors and for the two temperature sensors. A 16 channel buffered multiplexer is used to transfer the signals to the CPU board. An EEPROM memory for storing factory calibration coefficients of the sensor.

The input to the amplifier board comprises a 7V DC feed and CPU control signals for the PWM, the multiplexer and the EEPROM. When the module starts up, the calibration coefficients are read to the module CPU and then used for calculating the gas concentrations from the raw data received from the sensor multiplexer.

Figure 12

MiniTPX measuring unit

2.3.4 MiniOM oxygen sensor The miniOM sensor measures the concentration of Oxygen in the gas sample. The measurement is based on the magnetic properties of oxygen. The sensor measures the sound pressure generated in the air gap of the magnet at the 164 Hz operating frequency. Two microphones are used for detection and the Oxygen concentration is calculated from the RMS value of the difference of the microphone outputs. The measurement principle is described in more detail in section 2.2.2. O2 measurement”. The sensor consists of the following functional parts

• • •

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Pneumatic system Amplifier board MiniOM board