Hi all,

First post here.

I am working with a F5 and MKVI control system. We observed the SRV hunting and on further investigation found one channel on the TVSO had failed (Servo Output "T"). Initially we suspected this caused the issue but later found that the Suicide Relay was active for this channel, therefore this could not be the source of the problem. I calibrated the valve and at 0&100% everything looks good, however when i then use the Manual Verification the valve over shoots its setpoint and then starts to hunt. I have adjusted the Reg_Gain but there is no real observed change.

Any suggestions on troubleshooting is much appreciated.

 

Jason, a lot more background would be a good start.
How did you "observe the SRV hunting?
When did this problem start, or how were you made aware this was an issue?
Is it causing issues with unit performance?
Troubleshooting.
I would not start by adjusting the Reg_Gain value. These values are usually set during commissioning and should not require adjustment after that.
Have you performed a servo polarity check?
Have you checked the null bias current?
Since the SRV loop is actually a pressure control loop the position calibration is not as important as the gas control valves. But in manual control the valve should follow demand, not overshoot excessively, and not hunt. More background as to when this problem started would be a good start to help us make the best suggestions as what else to look at.

 

Apologies for the lack of information. The machine was started last week and almost immediately an operator observed the valve hunting. We also had seismic vibration alarms which we suspect could be due to pulsating caused by the fluctuations in the SRV valve position.

Today I went to do the servo polarity check and observed that the "T" channel, which was diagnosed as faulty, had been reconnected (I told the technician not to). The polarity check was good so I moved to manually stroke the valve again and this time the feedback was good for each command I gave, no overshoot or hunting. So, it turns out the reason I was observing the erratic behavior after calibration was because the "T" servo coil had been reconnected and I wasn't aware of this, my bad.

In the end it seems that there is a problem on the channel itself. I have verified the integrity of the "T" servo field side by shifting it to the "S" channel and it works fine, however when the field wiring for the "S" servo is connected to the "T" channel there is no change.

Cheers
Jason

 

JasonG, no apology needed or expected, only want to better understand the situation and try to help. I know from experience the time required to write a story that documents the situation so all can understand where you are at and what you have done. Curious to know what fixes the issue. If the "T" core output went into suicide then if that channel is the issue it would smooth things out I would expect. Possibly issue with the "T" core VSVO card? Good luck and keep in touch.

 

Hi MIKEVI,

It is an issue with the TSVO board. I totally agree with you regarding the suicide relay, with this activated it should smooth things out. The field wiring and servo coil for the "T" core are fine so there should be no reason for the suicide relay to activate. Another point to note is that when the wires are reconnected to the "T" channel it immediately begins to behave erratically, no manual reset required.
We are migrating to a MARK VIe system during our next outage so hopefully we can survive until then because spare parts are at a minimum here.

 

JasonG, cool to hear you are migrating to the 6e. I did that back in 2018, I hope you are performing a "Full" migration and not a "Platform upgrade". There are major differences between the two upgrade paths. Keeping the servo wires disconnected for the problematic core should be just fine, as long as another core doesn't get crazy it will be fine. I would place money on an issue with the VSVO card and not the TSVO terminal board, based on my past experience. But I can/could be wrong, would not be the first or last time for that.

 

I'm afraid it's the 6e migration kit. Most of the hardware is replaced with the exception of some TRLY boards I believe.

 

The full migration removes all the core racks, R+S+T and the VPRO's X+Y+Z. All black 37 pin cables from the VME racks to the terminal boards are removed. I/O packs are installed on the terminal boards along with power and ethernet cables. Some terminal boards require replacement since they are not compatible. TVIB+TSVO+TPRO+TBTC+TRTD+TTUR as I recall. New MKVIe controllers/switches/power supplies etc are installed where the MKVI and VPRO cores used to live. Good upgrade, hard to tell it was never a MKVIe.
Platform keeps all the racks, cables etc. Only removes the VPRO's, VCMI and UCVx cards, installs a PCMI and MKVIe controllers. Not a good upgrade IMHO.

 

Ah ok, ours is definitely the full migration then.