Teledyne T200, Руководство по эксплуатации, Страница: 315 / 425

Teledyne API
– T200 NO/NO
2
/NO
X
Analyzer Operation Manual Principles of Operation
313
13.3.4.2. WATCHDOG CIRCUITRY
The most important of the status LED‟s on the relay board is the red I
2
C bus watch-dog
LED. It is controlled directly by the analyzer‟s CPU over the I 2
C bus. Special circuitry
on the relay PCA watches the status of D1. Should this LED ever stay ON or OFF for
30 seconds, indicating that the CPU or I
2
C bus has stopped functioning, this Watchdog
Circuit automatically shuts all valves and turns off all heaters.
13.3.4.3. VALVE CONTROL
The relay board also hosts two valve driver chips, each of which can drive up four
valves. The main valve assembly in the T200 is the NO/NO
X
- Auto-zero solenoid valve
component mounted right in front of the NO
2
converter housing (see Figure 3-5).

These two valves are actuated with 12 V supplied from the relay board and under
the control of the CPU through the I
2
C bus.
Additional valve sets also controlled by the CPU via the I
2
C bus and the relay PCA can
be included in the T200 (see Table 1-1 and Sections 3.3.2.3, 3.3.2.4, and 3.3.2.5 for
descriptions of these valve sets).
06858E DCN7057