IGV calibration

Dears,

In SRV & GCV calibration 0% and 100% LVDT feedback can be found during manual stroke or Auto calibrate and entered into I/O configurator.

In IGV is concern, 100% is limited to 84 deg, so how to calculate 100% stroke value to enter into I/O configurator.

Somewhere I read y = mx + c (i am not clear) to be applied to find 100% stoke value.

I am expecting your feedback.

Cheers
G.Rajesh
 
Dear,

It sounds as if you are manually calibrating the LVDT feedback, as opposed to using AutoCalibrate.

If you choose to manually calibrate the IGV LVDT feedback, you will need to extrapolate the 0% (0 DGA) and 100% (100 DGA) values using basic math skills. You will have to collect voltage versus position values for at least two points, solve the two equations for the slope and offset, then determine the voltage readings for 0% (0 DGA) and 100% (100 DGA) values, then put these values in the appropriate I/O Configurator fields.

If you want to use AutoCalibrate, you need to measure the IGV angles at the mechanical full closed position (at the actuator stop) and also at the mechanical full open position (ring stop) and then put those values into ACALIB.DAT for the IGV servo-valve output (usually SVO5). Then execute an AutoCalibration and put the 0% (0 DGA) and 100% (100 DGA) values determined during AutoCalibrate into the I/O Configurator.
 
Thank you CSA,

We measured the actual angles when closed and open are 29 deg and 78 deg resp.

Our present ACALIB.DAT is

POSITION_NEG_SAT 84
POSITION_POS_SAT 34

So, before do Auto calibration if change the ACLIB.dat

POSITION_NEG_SAT 78
POSITION_POS_SAT 29

Will it the correct procedure to calculate 100% stroke value?

Your are the one helping us lot and explained which is not mentioned clearly in manuals.

Thank you
G.Rajesh
 
G.Rajesh,

You are correct about the changes required in ACALIB.DAT. Negative servo current opens the IGVs; positive servo current closes the IGVs. That's why the full open position goes on the POSITION_NEG_SAT line and the full closed position goes on the POSITION_POS_SAT line.

<b>HOWEVER,</b> I have a little trepidation about the full open angle measurement you cited. In the original post you said the 100% open condition was limited to 84 degrees, but you say you physically measured 79 degrees. Something doesn't add up very well.

Also, 29 degrees for the fully closed position is pretty far closed. Presuming a typical 34 DGA to 84DGA range, the stops are usually set for approximately 32 DGA and 86 DGA.

When you have obtained repeatable, reliable measurements then put the values in ACALIB.DAT as you have indicated, then use AutoCalibrate to calibrate the IGV LVDT feedback. Then verify the accuracy of the calibration.
 
Thank you CSA,

Sure, we'll measure the IGV angle again and come back with the result.

We are planning to move the 29 deg to 34 deg by adjusting the arm. Then measure the full open angle. Since angle came dowm to 29 deg from 34 after the maintenance.

G.Rajesh
 
G.Rajesh,

The mechanical stops are supposed to be set "outside" or "beyond" the operating region. For example, if the minimum operating angle is supposed to be 34 DGA, then the fully closed mechanical stop should be set to approximately 32 DGA, to be sure that the IGVs are not up against the stop when the Speedtronic is trying to modulate (control) the IGV angle to 34 DGA.

Now, this means that when 20TV-1 is de-energized and there is hydraulic pressure that the IGVs will move to an angle less than 34 DGA, but this is normal and to be expected because of how the IGVs are supposed to be adjusted and operated.

If the maximum operating angle is 84 DGA, then the fully open mechanical stop is supposed to set to approximately 86 DGA so that the IGVs are not up against the mechanical stop when the Speedtronic is trying to modulate (control) the IGV angle to 84 DGA.

Have a read of the Control Specification, Sect. 6. I believe you may (should) find some information there about how the mechanical stops should be set, in addition to the information about the operating range of the IGVs.

I believe there may also be some notes on the drawings for the IGV ring and IGV actuator which might help with understanding how the stops are to be set.

Again, the mechanical stops are *NOT* to be set to the operating range; they are to be set just slightly "outside" the operating range.

When you have made the adjustments to the mechanical stops and know the angles at each stop, then enter the positions in ACALIB.DAT in the SVO section for the IGV actuator (again, that's usually SVO5), save the changes and exit, then start AutoCalibrate and navigate to the IGV actuator page (usually SVO5); you should see the minimum and maximum angles you entered in ACALIB.DAT on the page (if typically configured). Proceed with the AutoCalibration at that point, verifying the results after the procedure.

Remember, there is usually as much as one (1)degree of "hysteresis" (movement) on an IGV blade when they are being held at some position by the actuator. This is important to remember when using a machinist's protractor to measure the IGV angles--because one must hold each blade being measured every time it's being measured in the same position in order to negate the hysteresis.

It's best to use some masking tape to mark the IGV blades being measured, and to mark them in the spot where the protractor is measured. (This is usually in the middle of the blade, along its length.) Again, make sure that each blade is held in the same position with respect to its "hysteresis".

Measuring IGV angles with a machinist's protractor is not easy, and it must be done with care and some degree of precision. One must measure the same blades each times and make sure to measure them in the same place along the length of the blade as well as holding them in the same position with respect to the hysteresis of the blade.
 
Dear CSA,
Thank you again for your reply.

We not done any adjustment as unit was started due to summer load.

We are closely watching the parameters like exhaust temperature and CPD.

Thank you
G.Rajesh
 
Can any one explain the step by step procedure of calibration procedure of IGV.

How to done changed in Mark V software, please describe the all step for easy understanding.

Thanks
 
Because the Mark V scales the LVDT's in percent, it expects the minimum and maximum LVDT voltages specified in the I/O Configuration to be for 0% and 100% of output command. However, the output command is in units of DGA.

Therefore, it is necessary to extrapolate the LVDT voltage from the measure values at the minimum and maximum stops to 0 and 100 DGA.<pre>
Y = mx + b

Where:
y = 100% stroke value to be installed in the I/O Configurator (LVDT_n_MAX)

(Opened actuator atopVRMS)-(Closed actuator stop VRMS)
m = ------------------------------------------
(Measured IGVangle@max stop)-(Measured IGV angle @ min stop)

x =100%
b = zero stroke value to be installed in the 1/0 Configurator (LVDT_n_MIN) LVDT offset

Example:

96TV-1
LVDT#1 VRMS= 0.706 @32deg.IGV angle(min stop)
VRMS= 3.028 @88deg.IGV angle(max stop)
96TV-2
LVDT#2 VRMS= 0.70l @32deg.IGV angle(min stop)
VRMS= 3.025 @88dog.IGV angle(max stop)

(3.028 VRMS - 0.706 VRMS)
m =-------------------------- =0.4146 VRMS/%
(88 deg - 32 deg)

for LVDT #1
b = (0.706 VRMS)-(0.04146*32)= -0.6208 VRMS
= LVDT_1_OFS value to be installed in the 1/0 Configurator LVDT1 zero
stroke.

y = (0.04146*100) + (-6.208) = 3.525 VRMS
= LVDT_1-MAX value to be installed in the 1/0 configuration LVDT 100% stroke.</pre>
After calculating the zero stroke and 100% stroke values for LVDT#1 and LVDT#2, put the new values in the TCQA I/O configurator.

Verify screen and exit.
Go to the MAIN MENU, select EEPROM DOWNLOADER and download the IOCFG section to <R, S, T> on TMR units and <R> on Simplex units.
Reboot affected processor, one at a time,
Refer to the Maintenance Manual (GEH-5980) for more information.

>Can any one explain the step by step
>procedure of calibration procedure of
>IGV.
>
>How to done changed in Mark V software,
>please describe the all step for easy
>understanding.
>
>Thanks
 
pascal,

I have a couple of questions.

First, I would ask why you aren't using AutoCalibrate. AutoCalibrate will do this "extrapolation" for you. (There won't be any maths errors when AutoCalibrate is used.)

Second, why didn't you explain how to measure the IGV angles at the minimum- and maximum mechanical stops? How does one move the IGVs to the minimum- and maximum mechanical stops to measure the angles?

Third, using this manual method why is it necessary to measure the IGVs at the minimum- and maximum mechanical stops? If you're just calculating the slope and offset of straight lines, does it matter where the two points are obtained?
 
Dear CSA

First of all, thank you for all your very very good advices and technical knownledges you are sharing with all of us we can all clearly see you skills.

Then to answer you questions above:

First question: I had some bad feedback with the first Mark5's on autocal not working properly, since then I always did it in manual, no matter what! also I like to "master" what is happening every step. I go on site to see if IGV (but also gas valves or secondary nozzle, etc.) are correctly opening and so on, this is the way I operate, sometimes a little tiring as the machine can be far form the control room but... my choice

And second the question was "step by step" procedure and I guess in my mind autocal is not a "step by step".

Second question: because you did it perfectly correctly on the post above. Going to minimum and maximum of the IGV rang is part of the manual command screen, and with this method I don't even need to know where are the mechanical stop as long as my "measure" reading during calibration are accurate (volt vs. DGA). As long as, you already pointed out, the mechanical stops are outside my operating controlled range

Third question: you are perfectly right we are computing a straight line, wherever the known points are will give exactly the same result, but for better accuracy points further apart will give more accurate results.

This is the method I used for many years now and I never had any discrepancy in my IGV reading and accuracy is as good (I guess because I did not use it) as autocal. But o course this is just for explanation I do not "ask" anyone to do the same as me, I am from the old school!

pascal
 
Everyone has their preferences, and in the absence of any documentation from GE everyone can do whatever they please--and they do.

I was just curious; that's all. I noted that you didn't include forcing 20TV-1 and didn't mention the "manual command" screen. Is that a User Defined (Demand) Display, or the Manual Position feature of the AutoCalibrate page? I didn't mention any display or positioning process.

And, step-by-step can be for any procedure if there is more than one step, be the procedure manual or automatic. Certainly, AutoCalibrate involves manually entering information into the I/O Configurator, downloading, and rebooting--so it's not really "automatic" in every sense, but it does do the calculations and extrapolations if the proper information is put into ACALIB.DAT.
 
Thank you all for your valuable reply.

we have done auto calibration

0% = -1.012V, 100% = 4.278 V. Measured angle at minimum is 34 and maximum is 84 (earlier it was measured 29 & 79 resp), so ACALIB.DAT not changed. So during next outage we are going put these valve into I/O configurator and verify the position.

Keep it up
G.Rajesh
Oman
 
During auto calibration the results are 0% = -1.012V, 100% = 4.278 V but in specification 0%= -0.763, 100% = 3.92. Why auto calibration result is differ from specification??

Before the auto calibration we have serviced our IGV cylinder and manually calibrated, found IGV normal.

G.Rajesh
 
What was the "zero-stroke" LVDT voltage, the voltage when the LVDTs were fully closed against the mechanical stop?

If it was more than approximately 0.700 VAC RMS then it would cause the 0% and 100% values to be elevated from normal.

And what's in the Control Specification for LVDT calibration values are just guidelines, not gospel.
 
Dear CSA,

0% = 0.825 Vrms, IGV angle in HMI screen is 35.1 DGA (Hydraulic pump is not running) 0% = 0.775 Vrms, IGV angle in HMI screen is 34.1 DGA (Hydraulic pump is running).

100 % = 3.085 (84 DGA)

Our problem here is when unit on cooldown it won't give start permissive as IGV is greater than 35 DGA (L3IGVFLT = 1).

Moreover parameters like exhaust temperature and CPD are same as other Frame-9E machine when both unit IGV at 84 DGA.

Hence we conclude problem MIGHT be in the lower angle. So if adjust the LVDT to 0.775 Vrms from 0.825 Vrms, will it solve the problem? OR auto calibrate valve to be downloaded to processor??

Take care
G.Rajesh
 
You have a bigger problem, G.Rajesh. If the IGV feedback is greater than approximately 34 DGA when the hydraulic pump is not running, and then it goes to 34 DGA when the hydraulic pump is running (presumably 20TV-1 is energized when the hydraulic pump is running and you're reporting this 34 DGA reading), then something is very wrong.

Look at the IGV P&ID (Piping Schematic). When 20TV-1 is de-energized and the hydraulic pump is running the IGVs should go to the fully "closed" position, which is less than 34 DGA (on most properly maintained machines). When the hydraulic pump is running and 20TV-1 is energized the IGVs should <b>open</b> to approximately 34 DGA as the hydraulic pressure is allowed to pass through to the IGV servo and the Mark V will adjust the current to make the IGVs go to the "closed" position, which is usually 34.0 DGA for most Frame 9Es.

You are telling us that when there is hydraulic pressure and 20TV-1 is energized the IGVs go to 34 DGA (okay; 34.1 DGA). But when the hydraulic pump is NOT running (and presumably 20TV-1 is de-energized) the IGVs <b>OPEN</b> past 34 DGA which is the exact opposite of what they should do.

The IGV LVDT voltage when the IGVs are fully "closed" against the mechanical stop should be 0.700 VAC RMS, +/- 0.020 VAC RMS. You are reporting a full 0.125 VAC RMS greater than that. Now, that may not hurt anything <b>as long as the IGV LVDT voltage doesn't exceed 3.500 VAC RMS when the IGVs are at the full "open" mechanical stop.</b>

When you perform an AutoCalibrate, are you physically measuring the IGV angles with a machinist's protractor, or are you using the indicator on the side of the axial compressor casing, or are you just clicking on AutoCalibrate and thinking that's all you need to do? To properly perform an AutoCalibrate you need to measure the IGV angles with a protractor at the fully "closed" and fully "open" positions, then put those values in ACALIB.DAT, then execute AutoCalibrate to obtain the 0%- and 100% stroke voltages, do a two-point verification of the LVDT feedback versus actual position (again, using a protractor), and if the verification is good then average the AutoCalibrate values (from <R>, <S>, and <T>) and put the average values in the I/O Configurator, download them to the three processors--and that's the END of the AutoCalibrate process.

The "zero stroke" voltage is not your problem. It's definitely not what it should be, but it's not your problem. Further, if you change the LVDT "zero stroke" voltage you <b>WILL NEED TO RECALIBRATE THE LVDT FEEDBACK.</b> If your IGVs are opening when they should be closing, that's your problem. Again, when the unit is shutting down and when 20TV-1 is de-energized there should still be hydraulic pressure and per the IGV P&ID that should cause the IGVs to move to the fully "closed" mechanical stop, which is usually around 32 DGA. If yours are moving to some angle greater than 34 DGA, that's a problem. And I suspect it's a combination of several things.

And, you are only reporting a single LVDT voltage feedback. There are two LVDTs; are they both reading exactly the same voltage and position?
 
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