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3700 Portable Samplers
Section 6 Servicing
6.3.3 Pump Control Board
201
205
Figure 6-7 Optical Counter PCB Component Layout
6-12
The pump control board (Figure 6-7) is an integral part of the
pump assembly and serves two functions: controlling the pump
motor and sensing pump revolutions.
The pump motor control consists of a 2-pole, double-throw relay
(K201) and transistor switches (Q201, Q202, and Q203). The
relay changes the pumping direction and will run the pump in
reverse when in the rest state. Each time the pump runs, the
microprocessor sends the pumping direction signal through pin 1
of P7, waits for the relay to change state, then starts the pump by
sending a high signal through pin 3 of P7. By waiting for the
relay to change state before applying power, you can prevent
arcing at the relay contacts.
The LED-photo transistor device (IC201) is a key element of the
pump revolution count sensor. Whenever the pump is running,
power is supplied to IC201. A rotating disk positioned between
the LED and photo transistor periodically interrupts the trans-
mitted signal. These interruptions create pulses, which are sent
back to the main board at pin 8 of P7 to be counted. The micro-
processor then uses these counts to determine the pumped
volume.
202
Q201
R203
R204
206
C
201
D
201
P201
203
R201
R202
207
K201
204
Q202
208 209
210
211
212
IC201
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