RADIOMETER TCM3 - Page 64

2. TCM3 TCM3 and TCM30 Service Manual
Analog PCB
Introduction The Analog PCB carries out the foilowing functions:
e Analog to digital conversion of the pO,, pCO, and other electrode signals.
+ Control of the electrode heat current and measurement of the electrode power
dissipation.
se Charging of the NiCd battery and supply of polarisation voltage and power to
the electrode and its pre-amplifiers.
e Constitution of the patient barrier, that is the transformer and the opto-couplers.
Three Versions Please note that three versions of the Analog PCB exist. The table below gives an
overview of the versions and their compatibility.
Part |. Used for Compatibility | Drawing
901-652 | TCM3 below R22 None 2369-A1
901-835 | TCM3 of R22 through R145 None 2440-A1
902-428 | TCM3 of R146 onwards and TCM30 | None 8423-A3
Electrode Input/ The electrode plug functions are transferred to A/D Converter 1 via the input
Output Circuit multiplexer QA10 and the voltage follower QAId. The transfer functions are:
MUX Signal Transfer Function, V(TP6)=
channel
0 2002 -14.7*V(pCO:in)-0.669
1
|p0,
V(pOsin)
2 Polarisation Voltage -680 mV
3 Thermistor 2 -0.1*(T - 10), Range 37-45 °C
4 Thermistor 1 -0.5*(T - 37), Range 37-45 °C
5 VaEAr -0.3(VroAp+20*ToAp)
6 JigAr -20*ILoan (maximum 53 mA)
7 Analog Ground 0
The CPU monitors the electrode power dissipation via R86.
If the electrode temperature exceeds 45.6 °C, the heat current is switched off
(QA3a, O1). Further, the heat voltage will be switched off.
The electrode power supplies, +5 V and -9 V, are protected against short circuits.
Continued on next page
» 49 1002N2.1