How to modify a 'software timer' setting in a GE MARK-IV control system?


Thread Starter


While starting our gas turbine (PG-6541) I've noticed that in combined cycle mode purge is completed in 8 minutes and in simple cycle mode purge completed in 5 minutes. however, it should be 13 minutes for CC mode and 8 minutes for SC mode.

I've studied the Elementary diagram of 'purge start' and 'purge complete' sequence and found the timer 'L2TVBB' software timer for 'Combined mode' and 'L2TVSC' software timer for 'Simple mode'. I've noticed that at rung display the timer 'L2TVBB' have the setting 7 minutes and 'L2TVSC' have the setting 4 minutes.

I've studied the literature to modify the timer setting, but that was not so helpful for me.

** it says:
1. Go to the 'Control Constant' (1D)
2. then select the specific timer
3. then select 'Adjust'
4. then write the 5 digit password
5. then write the three digit initial

here, (1 to 4) is understandable, but no.5 (three digit initial) is not understandable for me.

Please, help me modifying the timer setting so that i can set the time 12 minutes at 'L2TVBB' and 7 minutes at 'L2TVSC'.
Later versions of the Mark IV Speedtronic asked the user to enter his/her initials (a one, two or three alpha-character set) to try to keep track of "who" made changes. Personally, I never used my initials (the first three characters of my first, middle, and last name); I just entered ZZZ to be able to continue with making the changes--and to make anyone after me wonder who made the change.

So, you can see--this little scheme presumed the person making the changes would be honest and use their initials to identify them as the "culprit." There was no check the Mark IV could make to ensure the initials were actually those of the person making the changes, or prevent anyone from making any change using any three characters.

I find it odd you used the initials GE as your author "name" when posting this thread!!! ;)
Once you have entered the 5-digit password, you should have access to the Raise & Lower pushbuttons and can adjust the constant value (It will be very slow to adjust if you are online). Hope this helps
but i have another problem. there is not timer to select at control constant page. its empty..what should i do?


Sometimes a Control Constant which may have been added in the field does not appear in alphanumeric order in the list of Control Constants in Data List 1D. You may have to scroll through all the screens of the Control Constant Display to find the ones you're looking for.

If that doesn't work, then you would need to look at the sequencing running in the Mark IV to see if the Control Constant was actually named as shown in the Mark IV Speedtronic elementary. Sometimes, it was not possible to implement a "long" timer as easily as thought possible, so you might find a 60-second timer running through a counter with the number of minutes then passing through to the L2TV logic. It seems you have a late model of the Mark IV (newer) so you probably have Rung Display (Data List 12, if I recall correctly) to look at the actual sequencing running in the Mark IV. If not, you'll need a "dumb terminal" to connect to <C> to examine the sequencing to see exactly how the timers were implemented and if they were named as shown in the Mark IV Speedtronic elementary.

Hope this helps; please write back, GE, to let us know how you fare.

And what initials you used when making the change!
> but i have another problem. there is not timer to select at control constant
> page. its empty..what should i do?

See if you have constants K2TVBB and K2TVSC in your constants list. If I remember correctly, and if these constants used the convention I'm thinking of, even though the logical (L2TVSC, for example) showed a numerical timer value underneath the coil on the elementary, the constant started with a K instead of an L. (Also, the accumulator that counted up while it was timing started with a T, for example, T2TVSC.)