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FPG2 Pressure Hunting
Radio Frequency seems to trip FPG2.

Gas turbine frame-V machine got tripped on low inter-valve pressure. Checked and observed transmitter 96FG2A, 2B, 2C reading fluctuating in negative side. Transmitter checked and found it is ok. It was observed that when we are using walkie talkie in GCV/SRV area, pressure hunting and coming dowmn negative. Pressure transmitter is work on 0-5 VDC signal. Please guide me how can overcome this problem to avoid GT trip on radio frequency.

1 out of 1 members thought this post was helpful...

Don't take the radio near the pressure transmitter. What control system are you using?

1 out of 1 members thought this post was helpful...

How close was the radio? This isn't all that uncommon, we've had VFDs "spool up" when a radio transmits nearby, and I blew out the power supply in a WorkMaster once while triggering my radio next to it.

About the only thing that you can do is shield your transmitter better and put up signs warning of radio interference.

Dear CSA,

Our machine is frame-V with Mark-Vie control system.

We have faced problem of tripping the machine on walkie talkie use in Gas turbine accessory compartment. During use of walkie talkie, all three 96FG2A/2B/2C pressure transmitters value dropped and went to negative side.

We observed that when only walkie used inside the accessory compartment at any area, 96FG2A/2B/2C transmitters value went to negative side. Outside the accessory compartment gate, no effect on pressure transmitters.

Pressure transmitters are make: Dynisco
GCV/SRV compartment is inside the accessory compartment.

Right now we have given instructions to operator for not using walkie talkie.

Please guide us, how to overcome this radio frequency problem.

2 out of 2 members thought this post was helpful...

VKGUPTA,

The problem is most likely either of these two possibilities:

1) The wrong wire was used to connect the three P2 pressure transmitters to the Mark VIe. It should be twisted, shielded pair wire with a drain wire. I have seen many sites that tried to use single conductor wires, or un-shieleded, twisted pairs. Neither will work very well.

2) If twisted, shielded pairs were used then the shield drain wires were not properly grounded. Shield drain wires should be grounded AT ONE END ONLY.

This topic has been covered many times before on control.com, and on many other places on the World Wide Web. There may be two or three twisted, shielded pairs for each signal (the output of the transmitter).

If the Dynisco transmitters are four-wire transmitters, the power supply wiring should also be twisted, shielded pair wiring, and the shield drain wire should only be grounded at one end--just like with the signal wires.

The shield can be continuous all the way through, or it can be individually grounded--but no matter what, the shield drain wire of the entire "chain" or of individual lengths should be grounded at one end ONLY.

Here is a link to a crude drawing which might help:

http://control.com/thread/1373726311#1414703336

Hope this helps!

Please write back to let us know what you find.

Dear CSA,

Thanks for reply.
I will check grounding and shielding. After that i will revert to you.

Dear CSA,
Please find connection detail of 96FG2A at mark-vie end.

Transmitter is 4-wire. Signal type used +-5 Volts.


TBAI TB No-21 (P24VDC) & 23 (0VDC)
TBAI TB No-24 (Ret) & 41 (PCOM)

Its 20mA signal TB no-22 is vacant. I don't know, why it is vacant. In stead of TB No-22, it is connected 41 TB No.

All transmitters wiring connections done at per same mentioned above connection.

Parallel I am checking grounding and shielding of loop.

1 out of 1 members thought this post was helpful...

VKGUPTA,

It seems you are assuming the output of the transmitters is 4-20 mA, and if they were then the signal should be connected to the 20mA terminal. But, many of the four-wire transmitters used by packagers of GE-design heavy duty gas turbines had 0-5 VDC outputs, and if the 96FG-2A, -2B & -2C transmitters on the turbine at your site have a 0-5 VDC output then the signal should be connected to the RET terminal.

Look at GEH-6721, Vol. II, and go to the PAIC section and find the TBAI terminal board. There are diagrams for the various types of transmitters, including 4-20mA output types and 0-5 VDC output types.

You can look in ToolboxST and see how the input signals are configured, and I believe--based on the information provided that the 96FG-2x transmitter at your site have a 0-5 VDC output, and should be connected to the RET terminal for the input channel (6), and that would be terminal 24. Terminal 24 is the SIGNAL RETURN terminal, and terminal 41 is the PCOM (the "common") of the signal input to the TBAI.

So, it would seem the wires at the Mark VIe for 96FG-2A are terminated correctly for a 0-5 VDC input, with a 24 VDC supply signal.

Again, the shield drain wires of BOTH the transmitter power supply AND the transmitter output (the input to the TBAI) must be properly earthed (grounded; bonded) to avoid the type of radio interference you are describing.

Many of the four-wire transmitters used on GE-design heavy duty gas turbines also had earth terminals or an earthing wire which must be properly terminated, also. It's not enough to mount the transmitter on a painted surface; it must also be properly grounded/earthed/bonded.

Dear Sir,

I have checked wiring connections of transmitters. It is as below:

Drain wire connected to Mark-Vie End on earthing terminal bus bar. Transmitter End drain wire was opened, not connected any where.

Earthing is connected at only control room side. Still transmitters signals are going negative side.

One more thing, signal cable used 12P*0.5MM2. 6 pair used for 96FG2A/2B/2C transmitter and another 3 Pairs used for GCV LVDT wires.

During walkie talkie using, GCV position feedback not having problem. It is fine. Only Transmitters signal are dropping.

Kindly guide me for further checks.