Tinkering Around!

This implies as bridge supply voltage decreases even minutely, the o/p voltage increases, almost doubles.

2. WITH SENSOR CONNECTED BETWEEN 9B , 7B & 5B

1. Before connecting sensor, adjust HV to about 2 V. connect sensor and adjust HV pot such that voltage between 9B & 7B is 2 V
2. Connect meter between B/A 4(+) and B/A6(-) and adjust zero pot such that meter reads zero. If reading is negative, turn zero pot clockwise to increase
3. The useful meter reading range is from 0 to 1 V
4. 0 is 0% LEL and 1 V is 100% on which OR LED should light up. Adjust A1 , A2 to light up at 0.2 v and 0.6 v respectively.

3. Expt2:

VHV =2 V between 9B & 7B

VA1=6.76 V (setpoint for A1 using A1 pot) (voltage at pin 2 of IC5B)

VA2= 6.90 V(setpoint for A2 using A2 pot) (voltage at pin6 of IC5B)

V5B= 1 V (measured) (signal voltage)

Voutput (IC3B pin 7 buffer voltage)= 6.13 V

OR setpoint= 7.12 V (pin9 of IC5D)(OR opamp)

Ref voltage for IC3C = 6.2 V (pin4 o/p of IC2)

13. Typical Repair case of AE-4103

In this card, on pressing READ button, FAULT will come, otherwise, PILOT glows without problem. When bench testing, it was also damaging the sensor, though, in control room rack, sensor was not damaged, but FAULT used to come on pressing read.

Solution

The NOR gate IC CD4001 was malfunctioning. The logic was all ok. However, current was leaking to adjacent gates. Therefore, when read button was pressed, 12 V should appear on the o/p pin of gate, instead 8 V was appearing and voltage at other pins were also changing due to internal current leak inside the IC and subsequent loading of the output (the o/p is designed to source only 6.8 ma of current max). This was varying the control voltage at the SMPS IC , hence high voltages were appearing on the output (instead of set 2 volts) and damaging the sensor. Replaced the IC, card works ok now.