The flame scanner / Flame Scanner module calibration is in regards to a GE Mark V that is running a 7EA Gas Turbine.
We had a secondary flame scanner "crap" out on us so I had replaced it with an ITS Flame Scanner that followed GE spec. About two months after that install, we started getting a nuisance diagnostic alarms coming in on the Alarm Scanner, D_1748_R (S and T) "TCE1 Flame Detector #5 out of limits". They came in during zero speed, while the unit wasn't running. I dig some digging and found out that if the scanner is picking up an intensity of 2 Hz or more at zero speed, it will send this alarm.
Troubleshooting Methods
I decided to open up the flame scanner module and noticed each input channel had a zero and span POT (see picture below). I "assume", by looking in the IO configuration utility for the Mark V, the range would be from 0 - 255 pulses or 0 - 4080 hz. Converted, that would be 4080 hz. Mark V counts the pulses generated by the flame scanner in 1/16 of a second (255 * 16 = 4080). So at 4mA = 0 , 5mA = 256 Hz (per manual), and 20 mA = 4080 hz. If you are wondering, the constant for flame detection in our system, it is 16. Which again, would lead you to believe that the Mark V would "block" any signal lower than 5 mA. Not the case.
Since I did not want to remove the module from service, or risk breaking the unit, we had a spare module that I was able to perform some tests on. Using a calibrator, I sourced the module.
4mA = 58hz
5mA = 302hz
20mA = 3854
21mA = 4084.
I found this rather odd that 5mA was at 302hz, I would have though it would have to be 256hz. Anything under 3.873mA was 0hz. Again, should anything under 4.25 mA be zero? Am I missing something?
The manual mentions NOTHING about these POTs in the module so I am curious if anyone has any experience calibrating the channels?
For now, i put the ITS flame scanner in 3S and took the scanner that was in 3S (a GE one) and moved it to 4S. Solved the problem but did not solve my curiosity with it.
We had a secondary flame scanner "crap" out on us so I had replaced it with an ITS Flame Scanner that followed GE spec. About two months after that install, we started getting a nuisance diagnostic alarms coming in on the Alarm Scanner, D_1748_R (S and T) "TCE1 Flame Detector #5 out of limits". They came in during zero speed, while the unit wasn't running. I dig some digging and found out that if the scanner is picking up an intensity of 2 Hz or more at zero speed, it will send this alarm.
Troubleshooting Methods
- Hooked in series, a calibrator, to read the loop current, it was reading 3.7mA and the signal at the Mark V was reading 12 Hz. This was with the flame scanner removed from the can and the lens capped.
- According to the manual, a signal under 4.25mA should be reading ZERO.
- I sourced the flame scanner module with a calibrator and to get 12 Hz, it had to be sourced 4.0455 mA. Kind of odd!
- To rule out a cabling issue, I plugged can 4S cable into 3S and it worked without any issues... The same scanner read 3.54mA on that channel. This proved the cabling was fine.
- I looked up ITS flame scanner data sheet and noticed their sensitivity was > 4mA at 310 nm while GE flame scanner was > 5mA at 310 nm. It is possible that ITS flamer scanner is just a bit more sensitive causing it give a signal to the Mark V. What is odd, is when I took the ITS scanner and plugged it into 3S, I never got a diagnostic alarm. This had me intrigued.
- This had me confused and led to believe that the scanner would NOT pick up or generate an output signal less than 5mA, that is not true.
I decided to open up the flame scanner module and noticed each input channel had a zero and span POT (see picture below). I "assume", by looking in the IO configuration utility for the Mark V, the range would be from 0 - 255 pulses or 0 - 4080 hz. Converted, that would be 4080 hz. Mark V counts the pulses generated by the flame scanner in 1/16 of a second (255 * 16 = 4080). So at 4mA = 0 , 5mA = 256 Hz (per manual), and 20 mA = 4080 hz. If you are wondering, the constant for flame detection in our system, it is 16. Which again, would lead you to believe that the Mark V would "block" any signal lower than 5 mA. Not the case.
Since I did not want to remove the module from service, or risk breaking the unit, we had a spare module that I was able to perform some tests on. Using a calibrator, I sourced the module.
4mA = 58hz
5mA = 302hz
20mA = 3854
21mA = 4084.
I found this rather odd that 5mA was at 302hz, I would have though it would have to be 256hz. Anything under 3.873mA was 0hz. Again, should anything under 4.25 mA be zero? Am I missing something?
The manual mentions NOTHING about these POTs in the module so I am curious if anyone has any experience calibrating the channels?
For now, i put the ITS flame scanner in 3S and took the scanner that was in 3S (a GE one) and moved it to 4S. Solved the problem but did not solve my curiosity with it.