GE b30, Technical Reference Manual

Page: 51 / 252

E-PSM(P)W module introduction
1-37
Document no. 2044677-001
Temperature measurement unit
The NTC-resistor value in the probe depends on the patient’s temperature. It is measured with
the following principle described below.
The constant current source is supplied about 38
µ
A current through the temperature sensor
(YSI 400-series NTC resistor). The constant current is caused a voltage over the temperature
sensor (NTC resistor). The voltage over the temperature sensor is amplified in a differential
amplifier stage. The amplified voltage is transferred to a controller of the STP board through an
A/D converter.
Figure 21 Temperature measurement principle
Invasive blood pressure measurement unit
An is5 V voltage is supplied to the pressure transducer. The differential voltage, which
depends on the pressure and the supplied voltage, is calculated from the bridge connection
(see the formula below).
U
out
= U
in
×
pressure
×
5
µ
V, where U
in
is 5 V
⇒
U
out
= 25
µ
V
×
pressure [mmHg]
Pressure amplification is realized in the instrumentation amplifier. The gain of the amplifier is
set to keep the level of the signal transferred to the A/D converter within the measurement
range even when there are circumstantial offsets or offsets caused by the transducer. There is
a filter before the amplifier to attenuate high frequency disturbances.
d/dt
0
0
0
0
R
R
R
R
Temperature
sensors T1, T2
constant
current
source
Differential
amplifier
Defibrillation/ESD protection
resistors and diodes
To A/D
converter
0C:7k36
15C:3k54
25C:2k53
38C:1k30
45C: 984
P
S
M
_temp
_meas_prin
ciple.vsd
Ref2 Ref1
T2 T1
R R