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Teledyne API – Model T700 Dynamic Dilution Calibrator Principles of Operation
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10.3.4. VALVE DRIVER PCA
The valves that operate the T700 calibrator’s main source gas and diluent gas inputs are
controlled by a PCA that is attached directly to the input valve manifold (see Figure 3-5
or Figure 3-6). Like the relay PCA, the valve driver PCA communicates with T700’s
CPU through the m
otherboard over the I
2
C bus.
Figure 10-8: Status LED Locations – Valve Driver PCA
10.3.4.1. Valve Driver PCA Watchdog Indicator
The most important of the status LEDs on the relay PCA is the red I
2
C Bus watchdog
LED. It is controlled directly by the calibrator’s CPU over the I
2
C bus. Like the
watchdog LED on the relay PCA, should this LED ever stay ON or OFF for 30 seconds
if the CPU or I
2
C bus has stopped functioning, this Watchdog Circuit automatically
shuts all valves and turns off all heaters and lamps.
06873B DCN6388