Philips M3000A, Service Manual

Page: 54 / 293

Temperature and Invasive Blood Pressure (Temp/Press) measurement
38 Introduction to the Instrument
Temp Mode
Measurement Range: -1 to 45
o
C (30 to 113
o
F)
Safety
To ensure the safety of the patient, the patient-applied part is isolated from ground by opto-
couplers and a transformer. The circuit is also encapsulated in plastic.
Block Diagram
This illustration shows the block diagram of the Temp/Press circuit.
Theory of Operation
The signals progress through the circuit as follows:
Excitation Voltage
This supplies 5V
DC
to a connected transducer. If a short circuit is detected by this circuit, the
CPU switches the voltage source off (to reduce power consumption).
Input Protection Network
This provides protection for the rest of the circuit against defibrillator voltage, electrostatic
discharge, and any electromagnetic interference. The signal is passed on to the analog to
digital converter, and to the transducer detection circuit.
Excitation
Voltage
Transducer
Detection
Input Protection
Network
To and from
Temperature
Sensor
Resistor
Array
Current
Source
A/D
Converter CPU
ROM/RAM
To and from
System CPU
T
o
a
nd f
ro
m
pr
essu
re
t
ran
sdu
ce
r