Theory of Operation Teledyne API T703 Calibrator Operation Manual
158
Table 9-1: Relay Board Status LEDs
LED COLOR DESCRIPTION FUNCTION
D1 Red
Watchdog Circuit; I2C bus
operation. Blinks when I2C bus is operating properly
D2 Yellow Dry Air Pump Status When lit the zero air AC pump is running.
D3-6 SPARE
D7 Green Photometer Meas/Ref Valve When lit the valve open to REFERENCE
gas path
D8 SPARE
D9 Green Ext. Zero Air valve Status When lit the External Zero Air valve is
open
D10 - 14 SPARE
D15 Yellow Photometer Heater Status When lit the photometer UV lamp heater
is on
D16 Yellow O3 Generator Lamp Heater When lit the O3 generator UV lamp heater
is on

9.2.3.4. Relay PCA Watchdog Indicator (D1)

The most important of the status LEDs on the relay board is the red I2C Bus watchdog LED. It is controlled
directly by the calibrator’s CPU over the I2C 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 I2C bus has stopped
functioning) this Watchdog Circuit automatically shuts all valves and turns off all heaters and lamps.
07223B DCN6378