FSRMIN / Acceleration confusion


Thread Starter


We installed a Frame 6B GT in 1988 and in 2004 we upgraded our Mark IV to a Mark VI. After that time we seem to have many rocky starts.

It would appear to me that after the warm up the acceleration control drives the gas valve too far closed and we loose fire in some of the cans (we have 4 flame scanners). The valve reopens and relights the cans and eventually we make it up to sync in and everything is fine until 18 months later when they shut it down for its maintenance.

I started looking into the control constants to compare what we had in to the specs. I realize the specs are a “starting” point and the field control engineer may have to tweak the numbers a bit. I have been reading the control specs, our manuals and this site to try and understand how the FSRMIN works during acceleration. What I thought I understood in my MARK IV logic was that it did a linear interpolation based on two points (FSKMINU2 and FSKMIND(4)) When I look in my Mark VI logic FSKMINU2 is a 4 point array. So now I’m confused.

Here are some of the “discrepancies” on the control specs. I don't know why GE (Schenectady/ not field engineer)would have changed the specs when the algorithms look to be the same.

1988 2004 2004 2013
Mark IV Mark IV Mark VI Mark VI
Spec Found Spec Found

FSKMIND1 6.6 0.0 5.929 6.6
FSKMIND2 8.,2 8.2 7.366 8.2
FSKMIND3 9.8 0.0 8.800 9.8
FSKMIND4 11.3 0.0 10.6 11.8
FSKMINU2 11.0 0 4.0 4.0

Acceleration Reference during start up

FSKACC2 25.6 25.6 10.0 10.0

the algorithmn looks a bit different. On the old Mark IV the error between TNHA and TNHAR was multiplied by 25.6 FSR/N (?) but on the drawing , the multiplication symbol (X in circle) has a -6 next to it. Not quite sure what that means. But in the Mark VI it is just a multiplication sign and the units were %/%/sec.

One other change that the control engineer made in 2004 was that he said our diesel (starting means) was running too fast. We used to crank at 20% turbine speed but now we are at 16% which is 14 HM. On our 2nd start up the other day (first one flamed out), we were having problems and he had them push on the diesel throttle to hold it at 20%. He also had the controls in the FIRE mode for about 10 minutes. He had all four cans and when they went to AUTO it made we still flamed out one can but the turbine held in and the fire came back as it accelerated on up to full speed.

Could someone explain how the minimum FSR works and see if they make any sense of our numbers.