RADIOMETER TCM3 - Page 68

2. TCM3
TCM3 and TCM30 Service Manual
Analog PCB, Continued
Switching
Circuit for
External
Battery.
Patient Barrier
Power Supplies
Test Points on
901-652
OP 5 transfers the monitor on/off information to the Power Supply PCB. The
signal is activating/de-activating a FET switching transistor which prevents the
external battery from being discharged when the monitor is switched off.
The circuits related to the electrodes and thereby the patient, are galvanic isolated |
from the mains supply, the battery cassette and recorders, computers, etc.,
connected to the TCM3/30 15-pole D-connector.
This galvanic isolation, called the “Patient Barrier”, is constituted by the switching
transformer T1 and the opto-couplers.
The +5 VDC supply from the Main PCB is divided into 3 parts, each with separate
supply leads to ensure high stability.
The +5 V Analog for the operational amplifiers, measure references and electrode
supply. The +5 V Digital as pull-up source and for the input opto-coupler. The +5
V Reference for the A/D converter Flip-Flops.
The negative supplies are derived from the heat supply voltage, either directly
(QA3a) or via the - 9 V regulator, Q2, CR3, R62.
TP1 Electrode test option (Not used)
TP2 pCO, signal. V(TP2) =- 14.7 * V (Terminal 13) - 0.669
TP3 Polarisation voltage. - 680 mV.
TP4 Thermistor 1 signal. V(TP4) =- 0.5 * (T - 37). T = 37 - 45 °C
TPS Thermistor 2 signal. V(TPS) = - 0.1 * (T - 10). T = 37 - 45 °C
TP6 See the table on page 1
TP7 Switching transformer secondary voltage
TP8 Analog ground
TP9 Hæar signal. V(TP9) = - 20 * I ppcrrode
TP 10 Serial output data and pulse-width modulated signal for the analog output
TP il Serial input data
TP 12 +5 V/Reference
TP 13 NiCd battery voltage
TP 14 Reference Ground
TP 15 Notused
TP 16 Electrode Heat voltage
Continued on next page