Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 310)

Model 9110TH NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 290
8.5.8. STATUS LEDS & WATCH DOG CIRCUITRY
Thirteen LEDs are located on the analyzer’s relay board to indicate the status of the
analyzer’s heating zones and valves as well as a general operating watchdog indicator.
Table 11-2 shows the states of these LEDs and their respective functionality.
D3 (Yellow) – NO
2
Converter Heater
D4 (Yellow) – Manifold Heater
D2 (Yellow) – Reaction Cell Heater
D5(Yellow)
D6 (Yellow) – O
2
Sensor Heater
D7 (Green) – Zero / Span Valve Status
D8 (Green) – Sample / Cal Valve Status
D9 (Green ) – Auto / Zero Valve Status
D10 (Green) – NO
x
/ NO Valve Status
D1 (RED)
Watchdog
Indicator
Figure 8-23: Status LED Locations – Relay PCA
8.5.8.1. Watchdog Indicator (D1)
T he 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 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 turn off all heaters.