GE Cardiocap 5 Service Manual

							
Measurement Parameters 
6.4.7 STP board—Invasive blood pressure measurement section 
Isolated +5 V voltage is supplied to the pressure transducer. From the bridge connection a differential 
voltage, which depends on pressure and supplied voltage, is calculated (see the formula below). 
Uout = Uin × Pressure × 5 V 
where Uin = 5 V 
Uout = 25 V × Pressure [mmHg] 
Pressure amplification is realized in the instrumentation amplifier. Gain of the amplifier is set so that 
the level of the signal transferred to the A/D converter stays within the measurement range even when 
there are circumstantial offsets or offsets caused by the transducer. A filter before the amplifier 
attenuates high frequency disturbances. 
 
Figure 6-17. Pressure measurement principle 
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Cardiocap/5 Technical Reference Manual 
6.5 N-XOSAT or N-XNSAT optional pulse oximetry components 
6.5.1 Datex-Ohmeda enhanced pulse oximetry components (N-XOSAT option) 
The Datex-Ohmeda enhanced pulse oximetry option (N-XOSAT) consists of the following parts: 
• Sensor connector board and cable assembly 
• Datex-Ohmeda pulse oximetry board (OSAT board) 
• SpO2 interface board 
The measured SpO2, pulse rate values and status information are transmitted through the connector 
board/cable assembly to the pulse oximetry board, then transferred to the SpO2 interface board. 
Communication between the pulse oximetry board and the SpO2 interface board is established through 
an RS-232C serial interface. The SpO2 interface board transmits the measurement information to the 
module bus of the monitor through an RS485 serial interface. 
Serial communications connector 
The OSAT board includes a bi-directional (2-wire) serial communications port. The serial interface 
connector is a 14-pin, dual row header. The pin assignments are shown below. 
Pin Description Pin Description Pin Numbering 
1 
3 
5 
7 
9 
11 
13 
+5IN 
COMMON 
COMMON 
UNUSED 
RX- RECEIVE 
RESET (Active Low) 
NO CONNECT 
2 
4 
6 
8 
10 
12 
14 
COMMON 
NO CONNECT 
NO CONNECT 
TX- TRANSMIT 
CTS 
COMMON 
COMMON 
Pin 2
Pin1 
Connector viewed from solder side of board. 
Sensor interface connector 
The sensor interface connector is a 10 pin, dual row header. The pin assignments are shown below. 
Pin Description Pin Description Pin Numbering 
1 
3 
5 
7 
9 
DETECTOR ANODE 
ID RESISTOR COMMON 
NO CONNECT 
NO CONNECT 
IR CATHODE 
2 
4 
6 
8 
10 
DETECTOR RETURN 
LED ANODES 
ID RESISTOR # 1 
RED CATHODE 
NO CONNECT 
Pin 2
Pin 1 
Connector viewed from solder side of board. 
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Measurement Parameters 
6.5.2 Nellcor pulse oximetry components (N-XNSAT option) 
The Nellcor compatible pulse oximetry option (N-XNSAT consists of the following parts: 
• Sensor connector board and cable assembly 
• Nellcor pulse oximetry board (NSAT board) 
• SpO2 interface board 
Sensors can be plugged into the monitor directly or used with sensor extension cables available from 
Nellcor. Sensors plug into a 9-pin female connector (D-type) on the front of the monitor. This 
connector is mounted on a small PC board, the connector board. This two-board system consumes 
approximately 1.3 W of power. 
• The Nellcor pulse oximetry board is a surface-mounted PC board manufactured by Nellcor. It 
contains the signal processing electronics and software that are based on Nellcor stand-alone 
pulse oximeters. It is used with an internal preamplifier.   
• The connector board/cable assembly consists of the patient connector, the connector board, and 
the cable that connects to the pulse oximetry board. The connector board contains the sensor 
interface connector, a differential preamplifier, and EMI protection. It provides analog signals to 
the pulse oximetry board from the oximeter sensor through a preamplifier inferface cable. 
The measured SpO2, pulse rate values, and status information are transferred from the pulse oximetry 
board to the SpO2 interface board. Communication between the pulse oximetry board and the SpO2 
interface board is established through an RS-232C serial interface. The SpO2 interface board transmits 
the measurement information to the module bus of the monitor through an RS485 serial interface. 
Communication protocol jumper 
Jumpers on the Nellcor pulse oximetry board determine the interface used for communication. A 
jumper should always be installed on J6 (interface selection).   
NOTE: New, replacement boards may have jumpers installed on J5 (baud rate selection) and J6.  The 
jumper on J5 should be removed before installing the board. 
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Cardiocap/5 Technical Reference Manual 
6.5.3 SpO2 interface board (for N-XOSAT or N-XNSAT option) 
 
Figure 6-18. SpO2 interface board block diagram 
NOTE:  Two switches located on the board are not used and have no function with the Cardiocap/5. 
RS485 drivers 
The SpO2 interface board contains drivers for data and for module reset functions. They drive the 
RS485-type serial communication bus between the pulse oximetry unit and the Central Unit. Data 
transmission speed of the bus is 500 kbps. 
In addition to RS485 bus RESET, a Power-up reset keeps the RESET pin of the CPU active during power 
up for about 500 ms despite the state at the RS485 bus RESET. This is used to prevent the sending of 
RS485 data during the RESET of the module. 
Power supply, non-isolated section 
The power supply is a half bridge type, switched mode circuit, where the driver FETs are controlled by a 
quartz oscillator. The load of the half bridge is the primary of the isolation transformer. The voltage, 
+15 Vdirty from the Central Unit, is used as the supply voltage of the switched mode circuit. 
Power supply, isolated section 
The secondary voltages of the isolation transformer are rectified, filtered, and regulated. The voltages 
can be measured from the test connector (X11).  
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Measurement Parameters 
Opto isolation 
The serial communication bus signals between the pulse oximetry board and the Central Unit are 
transferred through the patient isolation section by high speed opto couplers. 
Microprocessor, UART, nonvolatile memory 
The microprocessor, with on-chip memory, converts and transfers data from the pulse oximetry board 
to the monitor.  
The UART provides bidirectional asynchronous serial communication between the pulse oximetry 
board and interface board CPU. 
Nonvolatile memory stores identification information, such as serial number, control number, date, etc. 
Module bus connector 
 
Pin No I/O Signal  Pin No I/O Signal 
1 I RESET_RS485*  14 I +32 VDIRTY 
2 I –15 VDC  15 I GroundDIRTY* 
3 I +15 VDIRTY*  16 I CTSC 
4 I +15 VDC  17 O RTSC 
5 I/O -DATA_RS485*  18 I RXDC 
6 I/O DATA_RS485*  19 O TXDC 
7 - Ground & Shield*  20 - ON/STANDBY 
8 I -RESET_RS485*  21 - BIT0IN 
9 I CTSB  22 - RXDD_RS232 
10 O RTSB  23 - TXDD_RS232 
11 I RXDB  24 I +5 VDC 
12 O TXDB  25 I +5 VDC 
13 - Ground & Shield*     
*Used in the OSAT or NSAT pulse oximetry unit 
Test connector 
Pin No Voltage Name Note 
1 +5V +5VTEST Supply voltage to the  SpO2 interface board 
2 +5V +5Vn Supply voltage to the pulse oximetry board 
3 +15V +15Vn Supply voltage to the pulse oximetry board 
4 - GND FGND 
5 - –15V –15Vn 
6 - - N/C 
 
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6.6 Airway gases and spirometry components 
Airway gas measurement involves the following components: 
• Gas sampling system 
• TPX measuring unit 
• OM measuring unit and OM board 
• PVX measuring unit and PVX board for Patient Spirometry (N-XV option) 
• CPU board 
6.6.1 Gas sampling system 
The gas sampling system draws a gas sample to the analyzers at a fixed rate. It also removes water 
and impurities from the gas sample. A sample line is connected to the water trap. The pump draws gas 
through the sampling line to the gas measuring units. After the measurements, the gas is exhausted 
from the sample gas out connector. 
 
Figure 6-19. Gas sampling system (N-XC option) 
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Measurement Parameters 
 
Figure 6-20. Gas sampling system (N-XCO and N-XCAiO options) 
D-fendTM
The sample is drawn through a sampling line to the water trap, where it is separated into a main flow 
and a side flow. The main flow is drawn through into the analyzers. A hydrophobic filter separates this 
flow from the patient side. The side flow creates a slight subatmospheric pressure within the D-fend 
water trap, causing fluid removed by the hydrophobic filter to collect in the bottle. 
Zero valve 
The main flow passes through a magnetic valve before proceeding to the analyzers. This valve is 
activated to establish the zero points for the TPX and OM units. When the valve is activated, room air is 
drawn into the internal system and the gas sensors. 
NafionTM tube 1) 
A Nafion tube between the water trap and the zero valve balances the sample gas humidity with that of 
ambient air. The tube prevents errors caused by the effect of water vapor on gas partial pressure when 
humid gases are measured after calibration with dry gases. 
Gas analyzers 
After passing through the zero valve and Nafion tube, the gas passes through the TPX and the OM 
units. The oxygen sensor has two inputs. One input accepts the main flow and the other draws in room 
air for reference. Both gas flows exit from a single port. 
                                                                        1) Nafion is a trademark of Perma Pure Inc. 
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Sample flow differential pressure transducer 
The sample flow differential pressure transducer measures pressure drop across the OM inlet restrictor 
and calculates sample flow from the pressure difference. 
Working pressure transducer 
The working pressure transducer measures absolute working pressure between the TPX unit and the 
OM unit. It is used for the “Occlusion,” “Check D-fend,” “Replace D-fend,” and “Check sample gas 
outlet” messages. 
Pneumatic unit 
The pneumatic unit contains a zeroing valve, an occlusion valve, and tubing connections. A series of 
restrictors and chambers form a pneumatic filter to prevent pressure oscillations from the pump to 
reach the measuring units. Zeroing and occlusion valve connections to room air include a dust filter.  
Occlusion valve 
The valve is activated when the sampling line becomes occluded. The main flow is diverted to the side 
flow of the D-fend water trap to remove the occlusion quickly. 
Sampling pump and damping chamber 
The gas sampling pump is a membrane pump that is run by a brushless DC motor. Sample flow is 
measured with a differential pressure transducer across a known restriction. The motor is 
automatically controlled to maintain a constant flow, even when the D-fend water trap ages and starts 
to get occluded. It also enables use of sample tubes with varying lengths and diameters.  
The damping chamber is used to even out the pulsating flow and silence the exhaust flow. 
NOTE: The flow is never reversed towards the patient. 
 
Figure 6-21. Gas tubing layout  
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Measurement Parameters 
6.6.2 TPX measuring unit  
The TPX unit 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 IR lamp is a 4W 
filament, surrounded by thermal isolation. A hole in the isolation passes the radiation to a conical,  
4 mm long measuring chamber.  
From the sample chamber, radiation goes into seven tubular light guides that have reflective inner 
surfaces. A thermopile detector with an optical filter in front of it is at the other end of each light guide. 
The temperature sensor measures the temperature of the TPX unit and is used for temperature 
compensation. 
 
Figure 6-22. TPX measuring unit 
6.6.3 OM measuring unit and board 
Oxygen measurement is based on paramagnetic susceptibility. The gas and the reference gas (usually 
room air) are conducted into a gap in an electromagnet. A strong magnetic field is switched on and off 
at a frequency of approximately 165 Hz. An alternating differential pressure is generated between the 
sample and reference inputs due to forces acting on the oxygen molecules in a magnetic field gradient. 
The pressure is measured with a sensitive differential transducer, rectified with a synchronous 
detector, and amplified to produce a DC voltage proportional to the oxygen partial pressure difference 
of the two gases. 
 
Figure 6-23. OM measuring unit 
OM board 
The Oxygen board contains the specific electronics for the oxygen sensor. Sample flow measurement 
and sampling system pressure sensors are on this board. It also contains EEPROMs that store 
calibration data of both the TPX and OM sensors. 
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6.6.4 PVX measuring unit and board (Patient Spirometry, N-XV option) 
NOTE: Never apply overpressure or negative pressure of more than 300 cmH2O to the flow and volume 
tubing. Differential pressure maximum is 25 cmH2O on one port at a time (when connecting tubes, for 
example). 
Patient Spirometry provides patient respiration monitoring capabilities using D-lite and Pedi-lite flow 
sensors. When Patient Spirometry is used, a special sensor (D-lite) replaces the normal airway adapter 
in the patient circuit. Double lumen tubing is attached to the two connectors on the adapter and on 
the monitor front panel.  
 
Figure 6-24. PVX measuring unit 
The measurement unit consists of airway connections, two pressure transducers, valves, and 
preamplifiers. The preamplifiers connect to the A/D converter on the main monitor CPU.  
Measurement is based on measuring the kinetic gas pressure and is performed using the Pitot effect. 
A pressure transducer measures the Pitot pressure. The signal is linearized and corrected according to 
the density of the gas. Flow speed is calculated from the pressure and TV is integrated from it.  
The breathing flow of a patient passing through the D-lite adapter creates a pressure difference. This 
pressure difference is measured by pressure transducer B1. Overpressure and negative pressure in 
airways are measured by pressure transducer B2. 
PVX board 
The Spirometry board connects to the Oxygen board. It contains pressure sensors for airway pressure 
and flow measurement differential pressure, and the preamplifiers for them. An EEPROM stores 
spirometry calibration data. 
6.6.5 Gas unit CPU board 
The gas unit CPU board contains the processor, memory, and A/D converters that are common to the 
whole unit. The board also contains TPX sensor preamplifiers and drivers for the valves, fan, pump, 
and lamp. The unit connects to the module bus through an RS485 serial channel. 
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