57
Valve Drivers
The solenoids are activated by transistors Q9 - Q13. To open the solenoid, a
0.5-second pulse of 22 volts is applied, then the voltage drops down to 12.5
volts to hold the solenoid open.
Pump Motor Driver/Cover Sensor
The pump driver circuit IC U9 and IC U10 provide the drive and control for
the peristaltic pump. Signals PUMPEN, Pump Enable and PUMPSTEP, Pump
Step Pulses enable IC U10 to provide the necessary control to driver IC U9
which supplies pump drive signals PHASE A through PHASE D to control
peristaltic pump operation.
IC U11 operates with signal DCLOSED from the sample door light gate to
provide signal DOOR which detects the status of the sample door (open or
closed).
Input Amplifiers
IC U13, U14 and U15 (9180/9181: U13 only) provide high to low input
impedance matching for each Electrode input. Offset generator IC U12D and
amplifiers IC U12A, U12B and U12C provide the necessary gain and offset for
each electrode channel. TP9, TP10 and TP11 provide test points for the Na
+
,
K
+
and Cl
-
/Ca
++
/Li channels respectively.
Temperature Sensor
This is an optional circuit which is used in the 9140, 9180 and 9181.
The circuit creates a temperature-dependent voltage which is converted by
software to degrees C. R54 can be adjusted for correct temperature setting.
Analog Channel Selector and A/D Converter
Analog inputs from the input amplifiers are selected via signals ADSEL0 through
ADSEL2 and are multiplexed by IC U19. This multiplexed signal is then fed to
the A/D Converter IC U20. IC U21 supplies the necessary reference voltage
(2500mV) for the A/D Converter and can be measured at TP14.
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