Our Frame-9E machine with Mark V control system. Recently SRV and GCV valves were serviced and fixed back after that it was noticed that the LVDT's feedback of the both valves reduced than before, what will the be correct action,

1. LVDT to be tuned to match with existing reading

<OR>

2. I/O cofigurator to be download to Mark V.

Thank you
G.Rajesh

 

Yes once the GCV/SRV is opened up for maintenance or overhaul, the LVDT calibration need to be done again. The only occasion you do not need the LVDT calibration is when you replace the servo valves. I believe there are quite a number of threads here discussing on the LVDT calibration so I would not discuss it over again. The whole calibration process is straight forward. Before you start, refer back to your control specs document on how much is the valve travel distance.
Post again should you need more details.
All the best!

 

Thanks Sd, I have read the past post regarding LVDT calibration. I am going to ask one clarification,

After SRV & GCV valve maintenance it's LVDT value reduced, say 0.678, we made into 0.693 to match with control specs, Is it correct?

Please clarify
Thanks
G.Rajesh

 

Definitely the voltage wont be the same after any maintenance work. The calibration is to made to match the total travel of the valve and NOT the voltage level of the LVDT. The voltage that we see is just the feedback from the LVDT on the position of the valves. Whats more important is to ensure what is the present voltage levels when the valve is fully closed and fully opened. These values will then be changed in the iocfg and later downloaded to the panel. The voltage level on the control specs is just as a reference only.
All the best 2u

 

Dear Sd,

if control specs for SRV (any one) 0% = 0.7001 and 100% = 3.001.

If, after maintenance it observed that 0% = 0.685 and 100% = 2.893.

If I download this new specs to processor, Will it affect the load or any other parameter?

Thanks in advance
G.Rajesh

 

An LVDT is a device which can be applied to many different types of valves, actuators, etc. with many different ranges of travel ("stroke"). An LVDT has a range of operation ("stroke") over which it's output is linear and proportional to the stroke of the device to which it is attached. And there are different LVDTs with different ranges of travel with similar output voltages (in other words, there are many LVDTs with outputs of 0.7-3.5 VAC RMS, but some have a range of travel of 1.5 inches, and some have a range of travel of 3.0 inches, and some have a range of travel of 6.0 inches, just as a few examples).

When one adjusts the zero stroke voltage, that's done to ensure that the LVDT will be operating in it's linear output range as the device to which it is attached is moved ("stroked"). The LVDT should be chosen such that it's voltage output will be linear over the physical stroke of the device to which it is attached.

When you set the zero stroke voltage of the LVDT, the full stroke voltage will be whatever it will be, and is <b>NOT</b> adjustable without affecting the zero stroke voltage. Which will affect the calibration of the feedback.

There is <b>no</b> independent method of adjusting <b>both</b> the zero stroke voltage <b>and</b> the 100% stroke voltage. And, because every LVDT's output is not identical to every other LVDT's output voltage, I would think it would be very difficult to have a specification that would work at both the zero stroke <b>and</b> 100% stroke setting. That's why LVDT feedback has to be calibrated, because the outputs of no two LVDTs are identical and can't be made to be identical because there is no independent adjustment of both zero- and 100% stroke voltages. And because LVDTs can be applied to many different types of devices.

If it was possible to adjust the zero- and 100% stroke voltages to be certain values, we wouldn't have to calibrate the LVDT feedback. That would be the calibration. Calibration involves "coordinating" various possible voltages to positions.

I have never personally seen a Control Specification list a particular or specific 100% stroke voltage for any LVDT. They usually list the range of linear output, say from 0.700 VAC to 3.500 VAC (which is the typical GE specification for LVDTs used on various devices).

It's been said many times before on control.com: Read any GE documentation for INTENT, not content. Sometimes it's literal; mostly it's not. There is only one physical adjustment that can be made to the LVDT, and if you set it at one position (zero stroke) and then change it at another position, it's not going to work correctly.

So, once you set the zero stroke voltage (which is done to ensure the LVDT output will be linear over the range of travel of the device to which it is attached), the 100% stroke voltage will be whatever it is when the device is at 100% stroke. And the calibration of the voltage feedbacks will reflect that.

It doesn't matter if the 100% stroke voltage is 1.67 VAC RMS, or 2.39 VAC RMS, or 3.02 VAC RMS, or 3.47 VAC RMS--as long as the LVDT output voltage is linear over the range of travel of the device to which the LVDT is attached. And, if you set the zero stroke voltage properly (to 0.700 VAC RMS, +/- 0.020 VAC RMS), then you can be pretty safely assured that it will be, linear, that is. And let the Speedtronic handle the "calibration" of the LVDT voltage feedback.

Again, the LVDT voltage values in the Control Specification are <b>not typically</b> the values that can be achieved or set in the field. The zero stroke voltage is the important value, and it should usually be 0.700 VAC RMS, +/-0.02 VAC RMS in order to ensure that the output of the LVDT is linear as the device to which it is attached is "stroked". And if the zero stroke voltage is set correctly, then the output of the LVDT will be linear with respect to position as the device moves, and the calibration feature will be able to convert the voltages at zero and 100% stroke to percentages of stroke. And, those should be verified by measuring the stroke of the device to which the LVDT is attached.

The Speedtronic doesn't even care what the zero stroke voltage is; that's a function of the way the LVDT is designed and built and chosen and applied. As long as the output is linear over the range of the travel of the device the LVDT is attached to, the Speedtronic can calibrate the LVDT voltage feedback. If the output was linear from 0.35 VAC RMS to 2.5 VAC RMS, as long as the output didn't exceed 2.5 VAC RMS when the device was at full stroke and the zero stroke was set to 0.35 VAC RMS, the Speedtronic can calibrate the feedback.

It's as simple as that.

But it can be, and has been, made a lot more complicated than that. As everything can be if one doesn't step back and look at the "big picture."

 

Thank you CSA, we will stroke the valves after two days and back with the feedback.

G.Rajesh

 

Dear CSA / Sd,

Please clarify this one,

If SRV I/O conf. download to processor, Is it necessary to change the regulator type from 77 to 43 (since SRV is a pressure feedback control)?

I think during auto calibrate regulator type won't be a problem.

Thanks
G.Rajesh

 

G.Rajesh,

The Mark V Application Manual, GEH-6195, describes the various regulators, in Sect. 7, I believe. Also, I believe the block in the CSP for the servo-valve output for the SRV shows how it is re-configured when it's in calibration mode. But I know the description is somewhere in written documentation, if not written literally then it's drawn graphically.

But, when you are using AutoCalibrate for the SRV the regulator is automatically reconfigured from a pressure control loop with position feedback to a straight position loop so the position feedback can be calibrated. (The same thing happens when calibrating LVDT feedback for a liquid fuel bypass valve with LVDT feedback, for anyone else reading this who might have this same question. The regulator is reconfigured from a flow control loop with position feedback to a straight position control loop so the position feedback can be calibrated.)

In other words, if you're using AutoCalibrate there is no need to re-configure regulators using the I/O Configurator. It would be a redundant step, that would require another download and reboot to undo.

If you've been using AutoCalibrate to manually stroke the valve, you shouldn't have needed to reconfigure the regulator. So, the logical extension would be that when performing an AutoCalibration it would behave similarly.

 

Dear CSA,
Thanks,

Yes, I agree with you during manual calibration L3ADJ will enable and give permission for calibration, it may reconfigure the regulator.

My doubt is, when downloading I/O configuatior to the processor, Is it necessary to change the regulator type. (for example SRV regulator type 77 to 43)

May be I am not understand clearly the past post, Please clarify this
G.Rajesh

 

G.Rajesh,

Maybe you don't understand the reply?

MAYBE?

The only reason it might be necessary to change a device's regulator type is if it's not a straight position loop regulator (Type 4n) and you're trying to manually stroke the device without using AutoCalibrate's manual position feature to check or calibrate LVDT feedback. The only devices which do not use straight position loop regulators are the SRV and Liquid Fuel Bypass Valves (and not all LFBVs have LVDTs).

In the past, before AutoCalibrate was released and then when there was this false rumor that AutoCalibrate didn't work properly on the Mark V after it was released, it was necessary to manually reconfigure the SRV regulator by changing the regulator's type in the I/O Configurator, downloading to- and rebooting the processors, gathering the LVDT feedback calibration data manually, inputting the data into the I/O Configurator, downloading to- and rebooting processors, verifying the calibration, making any necessary changes to the data in the I/O Configurator, downloading to- and rebooting the processors, verifying the calibration, then once the calibration was satisfactory it was necessary to change the regulator type back to the original value in the I/O Configurator, download to- and reboot the processors. User Defined (Demand) Displays were usually used to enter the manual position reference for stroking the SRV (not AutoCalibrate's manual positioning feature) to get the LVDT feedback data.

When using AutoCalibrate, you select the SRV, enable AutoCalibrate and the TCQA card automatically changes the regulator type, strokes the SRV and gathers the LVDT feedback data, looks at the information in ACALIB.DAT and calculates the proper I/O Configuration Constants and changes the TCQA RAM values to the proper values, and when AutoCalibration is finished it resets the regulator type back to the proper value for running the turbine. All that's left for a user to do is put the LVDT feedback values that were calculated by AutoCalibrate into the I/O Configurator, download them to the processors and reboot them. No regulator change necessary. Not before. Not after. Not at all. Not ever. Never.

If you're stroking the SRV (which does not use a straight position loop regulator) using AutoCalibrate's manual position feature, then AutoCalibrate is <b>already</b> changing the regulator type for you! (Unless you're manually changing the regulator type before using AutoCalibrate. In which case, you're wasting a lot of time unnecessarily performing downloads and reboots.)

 

Dear CSA,

At first thank you for your reply.

Please don't bother, i hope you won't.

What is the difference between, checking the LVDT feedback in the user defined display and autocalibrate manual mode?

One more clarification, during Autocalibrate, there is no need to re-boot the processor, is it? as it will change the RAM value directly.

Your advice please

Thanks
G.Rajesh

 

Dear All,

Could anybody clear this doubt,

What is the difference between, checking the LVDT feedback in the user defined display and auto-calibrate manual mode?

Thanks
G.Rajesh