Pressure Module, M-P and Pressure Temp Module, M-PT
Document No. 800 1013-1
7
The P3 signal is transmitted as a pulse width modulated (PWM) signal over the patient isolation.
The analog signal is generated by low-pass filtering the PWM signal.
Microprocessor unit
The microprocessor uses the Intel 80C196KC-16 which includes three A/D converters and a UART.
There are external memories, an 8-bit data bus, a 16 MHz oscillator, an open collector reset, and a
watchdog timer. The internal UART communicates and transfers data between the module and the
CPU board in the monitor.
High speed I/O is used to obtain pulse control sequence necessary for pulse oximetry
measurement. It receives its timing clock from the oscillator.
Invasive blood pressure measurement unit
An is5 V supply is connected to the input of the pressure transducer bridge circuit. From
the bridge circuit output a differential voltage, which depends on blood pressure and input supply
voltage, is calculated using the following formula:
Uout = Uin
×
Pressure
×
5 V
where Uin = 5 V
Uout = 25 V
×
Pressure [mmHg]
Pressure amplification is performed by the instrumentation amplifier. The 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 pressure transducer. The
input filter before the amplifier attenuates high frequency disturbances.
Input
Filter
Instrumentation
amplifier
to AD converter
Pressure
transducer
Vin
Vout
G
Figure 4
Pressure transducer principle of operation
Temperature measurement unit
Value of NTC-resistor in the probe depends on patient’s temperature. It is measured with the
following principle.
The temperature signal(s) is produced by voltage dividers, part of which is the patient probe (YSI
400-series thermistor). The output is amplified by the calibrated amplifier(s) whose offset voltage
makes its output spread on both sides of zero. Wider output range (measurement range) means
better resolution.
