Fukuda Denshi HC-530, Service Manual

Page: 78 / 202

Chapter 8
●
PCB-6619
（
TCP BOARD
）
The TCP board is dedicated to the HC-530 module. The board contains an input
amplifier, a multiplexer and A/D converter circuit, an overheat detector, a
heater current limiter, a heater voltage controller, and a heating controller.
Input Amplifier
The input amplifier amplifies the input signals from the input connector and
sends the amplified signals to the multiplexer.
Multiplexer and A/D Converter
The multiplexer and A/D converter circuit receives the amplified signals from
the input amplifier and multiplexes them using the 8-channel multiplexer
(IC20).
Signals input to the multiplexer are summarized as follows:
Channel
number
Signal
name
Description Input level Input range
0 pCO2 pCO2 input
‐
14.7V
pCO2
‐
0.669 5
～
200mmHg
1 pO2 pO2 input V
pO2
0
～
800mmHg
2
‐
680mV Monitoring of
pO2 electrode
polarization
voltage
‐
680mV
3 Therm2 Electrode
temperature
(for safety
circuit)
‐
0.1(T
－
10) 5
～
57
℃
4 GND Ground
(for A/D
adjustment)
0V
5 therm1 Electrode
temperature
(for heater
control)
‐
0.5(T
－
37) 36.5
～
47.0
℃
6 Vheat Heater voltage
‐
0.3(V
LOAD
+20I
LOAD
)
‐
11.8
～‐
14.7V
7 Iheat Heater current
‐
20I
LOAD
0
～
53mA
This circuit then converts the multiplexed signal to digital signals using the
16-bit A/D converter (IC16). The sampling time is 1 kHz. The converted signals
are sent as serial data to the I/F board through CN2.
Overheat Detector
The overheat detector compares the therm2 signal using the comparator
(IC14A). When the temperature exceeds 45.6
0
C, this circuit outputs an
overheat signal to shut down the power supply to the electrodes.
This circuit also sends the overheat signal to the I/F board via CN3, so the signal
is applied to INPORT2 and used for error processing.
Heater Current Limiter
The heater current limiter controls the transistor (Q4) to limit the maximum
current flowing to the electrode heaters to 53 mA.
8 - 14