Mark-V control system has been used in VGTPS. Hydraulic servo valve with lvdt moog make is used for Gas Turbine fuel gas system. Now the SRV was oil leakage obtained. So, the defect will be replaced by the new SRV actuator with RVDT moog make. Whether the RVDT is suitable for our existing Mark-V system TBQA, TBQB and TBQC.

Please reply to this question

Perumal
AE/C&I/PH-I
VGTPS/Ramnad

 

The Mark V can use any position feedback device that is excited with AC and puts out a differential voltage that is, for some range (electrical and mechanical) linear with position. RVDTs and LVDTs both work.

The RVDTs that were used on many MOOG-produced valves have typically had a slightly different linear range--on the order of 0.5 VAC RMS to approximately 2.5 VAC RMS (for 0-90 degrees of motion). If you try to use the 0.7 VAC RMS for zero stroke usually the feedback becomes non-linear near the full open (90 degree) position.

I suggest you connect the RVDTs to the Mark V, and measure and record the "as-found" zero stroke voltages (with a True AC RMS voltmeter). Then, try to stroke the device to full open while recording the feedback positions/voltages and see what the full stroke voltage is and record that. (It may not stroke open, or fully open, if the RVDT voltage range is different from the LVDT.) If the feedback is non-linear while opening the SRV, or the SRV is unstable, I would suggest setting the RVDT zero stroke voltage to 0.500 VAC RMS (+/-0.100 VAC RMS), performing an AutoCalibration, and then opening the valve slowing while measuring and recording the feedback.

It may also be necessary to change the servo regulator gain value--if the supplier used a different servo-valve on the new actuator. If the servo-valve is different, you should contact GE for the proper current gain value for the actuator and servo-valve. (If the servo-valve is the same as on the old actuator, it shouldn't be necessary to change the regulator current gain.)

Please write back to let us know how you fare!

Again, the Mark V doesn't care what the linear range of feedback is--as long as it's linear with stroke. That occurs for most LVDTs that the OEM uses between 0.7 VAC RMS and 3.5 VAC RMS (not those exact values, but with the zero stroke position set to 0.700 VAC RMS, +/- 0.200 VAC RMS, the output at full stroke should not exceed 3.5 VAC RMS. For some RVDTs used on SRVs, the linear range, if the zero stroke voltage was set to 0.7 VAC RMS, would exceed the range of travel and be non-linear near the full open stroke. So, it is necessary to lower the zero stroke voltage to ensure the feedback at maximum stroke is in the linear range of the RVDT. (The Mark V doesn't care what the linear range of the position feedback device--as long as the output is linear over the mechanical range of travel of the device. So, one can use LVDTs with any linear output range--as long as the output is linear with the device's stroke (range of travel).)

Hope this helps! Please write back to let us know how you fare!

 

Actually, I've been asked to clarify this statement:

>The Mark V can use any position feedback device that is
>excited with AC and puts out a differential voltage that is,
>for some range (electrical and mechanical) linear with
>position. RVDTs and LVDTs both work.

The Mark V can only produce LVDT excitation voltage of approximately 7.0 VAC RMS, at approximately 3.0 kHz. So, any position feedback device that can produce a differential output voltage with an excitation of approximately 7.0 VAC RMS at approximately 3.0 kHz can be used for position feedback with a Mark V turbine control system--as long as there is some region that the output voltage is linear with position.

Sorry for any confusion!