DIAPHRAM SEALED TRANSMITTER CALIBARTION ERROR

[EthyleneInstrument]

Firstly this is my first subject,Thanks for your response

I want to mesure level of tank which is replaced in column.
There are only 2 flanges to mesure level.
Steps of my calibration and problem:
Firstly I turn of 2 block valves which is replaced between flange and column.
Secondlly I replaced the diaphragm seals of yokogawa EJX118A on both of 2 flanges.
thirdly I opened drain(vent valve) valves of flanges.
Fourtly I connect yokogawa EJX118A with BT200 hand terminal and, I made zero calibration (after diaphram seals connected).
Fiftly I send value of span (184mmH2O) to transmitter.
sixtly I closed drain valves and opened block valves.
but When I looked at level Gauge , there is no level, but our transmitter shows 15% level.
I couldnt understand why 15% level occur?
I drained Level Gauge, but there isn't any proplem with level Gauge. There is not any level in tank. but gas of fluid filled in tank and pressure is about 21 bar.

I make these 6 steps, again but it shows same level.

note: process preesure of column is 21 bar
process temperature: -20 degrees celcius
Note2: Diaphram seals filled with ethylne glicol. So it can work at 20 to -50 degrees celcius. So that temperature (-20)musn't be problem

Can you offer something.

Thanks

 

[IRstuff]

I'm confused.

> Did you calibrate with 21 bar pressure?
> According to the manual, zero level is supposed to be 50mm above the high pressure end.
> Is the transmitter located per manual instructions?
> Is your span correct? 21 bar corresponds to water pressure at about 200 m depth.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[danw2]

For us US guys, a 184mm span is only 7+ inches of water column.

A 15% error on 184" is only an inch, which is a lot of zero error for direct mount DP, but we're talking remote seals here.

My copy of a Yokogawa brochure for PI remote seals says,
"Ranges: From 10" H2O to max flange rating"
10" H2O is ~250mm H2O, give or take, yet your span of 184mm is ~30% less than the minimum listed. Are you working on the edge here? Is there some non-repeatability factor introduced at this low span?

What diameter seals are connected to the process?

Is your 15% zero error observable at the same temperature as the zero set was done, or at a different temperature?

You set zero at atmospheric pressure and are now checking zero at 21 bar. If you set zero at the elevated tank pressure (21 bar), does the zero offset disappear at atmospheric?

Who installed the seals on the transmitter? Yokogawa at its factory, a nationally recognized seal installer, your local gauge guy, or someone in your shop?

 

[EthyleneInstrument]

I want to say process pressure, not URL value ,
process pressure is 21bar.

flange to flange distance is 35cm.
density is 0.52gr/cm3.

so span is : 35cm X 0.525gr/cm3= 184mmH2O

Secondly I replaced DP under high seal,
about 150mm above high seal

 

[EthyleneInstrument]

sory, I wanna say below,

"Secondly I replaced DP under high seal, about 150mm below high seal "

 

[danw2]

OK so this is what you have:

What is the diameter D of the seals are connected to the process?

Is your 15% zero error observable at the same temperature as the zero set was done, or at a different temperature?

You set zero at atmospheric pressure and are now checking zero at 21 bar. If you set zero at the elevated tank pressure (21 bar), does the zero offset disappear at atmospheric?

Who installed the seals on the transmitter? Yokogawa at its factory, a nationally recognized seal installer, your local gauge guy, or someone in your shop?

 

[danw2]

Your URV will not be 184mm. That's the maximum head pressure or the span, but it is not the URV, which requires compensation for the constant fill fluid head pressure.

I have always calculated the LRV and URV, entered the LRV, corrected for installation measurement error, and then recalcuated the URV and entered the corrected value.

LRV calculation is the head pressure of the fill fluid pulling down on the upper seal and pushing on the lower seal. It is the elevation distance between the upper and lower seals times the specific gravity of the fill fluid.

Yokogawa's specific gravity for ethylene glycol = 1.09 (pg 37, table 8.1, IM 01C25H01-01E)

350mm distance between flanges:
-350mm H2O * 1.09 = -381.5mm H2O = LRV (it's a negative value)

If the distance is not exactly 350mm, then the measured 'zero' point will vary from 0.00 by the amount that the LRV calculation is in error, because of an estimated elevation distance that is in error and temperature error of a filled system.

The LRV is corrected by adding or subtracting the amount of zero error to the "estimated" value, which will then correct the zero measurement reading to 0.00.

The URV calc is based on the maximum liquid head pressure (span) added to the LRV (the URV is not 'just' the maximum head pressure span of 184mm H2O).

The maximum liquid head pressure (span) is the elevation distance of the liquid, 350mm * SG = 184mm H2O, (SG = 0.525) as you calculated (but this is maximum head pressure, NOT the URV):

184mm head pressure added to the LRV of -381.5 =
+184mm - 381.5mm = -197.5mm H2O

Why don't you enter the LRV of -382mm H2O and see how far off the measurement is?

Then, correct the LRV by adding or subtracting the actual offset to -382 until the zero point reads 0.00?

Then add the 184mm max head pressure span to the actual LRV measurement value and enter that as your URV.

Dan

 

[EthyleneInstrument]

transmitter order code is written below
Brand:Yokogawa
Order Code: EJX118A-DMSCG-912DB-WA22B1SW20-EA22 / KF21 / X2
So flange sizes is 2" 300#

I know that there are 2 types of calibration.
firstly replace 2 flange neighbourhood (replace it on the same height) , make zero calibration as you discribed "Yokogawa's specific gravity for ethylene glycol = 1.09 (pg 37, table 8.1, IM 01C25H01-01E)350mm distance between flanges:-350mm H2O * 1.09 = -381.5mm H2O = LRV (it's a negative value)If the distance is not exactly 350mm, then the measured 'zero' point will vary from 0.00 by the amount that the LRV calculation is in error, because of an estimated elevation distance that is in error and temperature error of a filled system. The LRV is corrected by adding or subtracting the amount of zero error to the "estimated" value, which will then correct the zero measurement reading to 0.00.The URV calc is based on the maximum liquid head pressure (span) added to the LRV (the URV is not 'just' the maximum head pressure span of 184mm H2O).The maximum liquid head pressure (span) is the elevation distance of the liquid, 350mm * SG = 184mm H2O, (SG = 0.525) as you calculated (but this is maximum head pressure, NOT the URV):184mm head pressure added to the LRV of -381.5 =+184mm - 381.5mm = -197.5mm H2OWhy don't you enter the LRV of -382mm H2O and see how far off the measurement is? Then, correct the LRV by adding or subtracting the actual offset to -382 until the zero point reads 0.00? Then add the 184mm max head pressure span to the actual LRV measurement value and enter that as your URV."


Second type of calibration.
Make zero calibration when you replace flanges on two column(make zero calibration when there is a difference of height).
make zero calibration (So We change zero division). At this time when we put 2 flanges neighbourhood, ?t gives error.
After that we send URL value of transmitter 184mmH2O.

 

[danw2]

You tried an auto-zero at atmospheric pressure. At the 21 bar operating pressure, the zero shifts 15%.

Yokogawa's remote seal guide cites a minimum span 250mm (H2O) for the M capsule:

Your span is 74% of minimum, 184mm.

Yokogawa's remote seal guide cites a minimum distance for the transmitter to be below the upper seal of 600mm:

Your distance below the upper seal is 150mm.

I don't know how either of these factors contribute to zero shift error, but each violates recommended installation procedure.

I don't know whether you require an accurate zero at atmospheric pressure or an accurate zero at your operating pressure of 21bar.

If an accurate zero at 21 bar is required, then you should consider auto-zeroing at that pressure and seeing what the zero shift is after the auto-zero.

You'll only see the effect of trying to use 184mm as a URV once you put liquid in the tank and see the response of the 4-20mA. Until then, you might want to work on the zero shift issue.

 

[EthyleneInstrument]

this DP can work at 184mmH2O URV.
because As u see, ? make an experiment with this DP in my work shop.
Please look at pictures

 

[EthyleneInstrument]

please look at this pictures, file attached

 

[EthyleneInstrument]

DANW2 thank There will be another experiment tomorrow.
Can u look at attached file.
THANKS

 

[EthyleneInstrument]

You know that, my DP is filled with ethylen glicol.
its density is 1.09gr/cm3 at atmospheric temperature.

But after I replaced both of 2 seals. Fill fluid density will be changed. because temperature of tank has too low temperature.

But which density of fill fluid will occur.

The tank which I replaced diaphraghm seals has -20 to -30 degrees celcius. and its pressure is 21, 22, 23 bar. (between 20 to 24bars)

Is there anyone can helpme?

note: DP Brand:Yokogawa
Order Code: EJX118A-DMSCG-912DB-WA22B1SW20-EA22 / KF21 / X2

 

[EthyleneInstrument]

yokogawa installed the seals on the transmitter.

so ? bought order code of EJX118A-DMSCG-912DB-WA22B1SW20-EA22 / KF21 / X2 .
,
yokogawa instlalled it in their factory.

 

[EthyleneInstrument]

fistly I set zero calibration , after I replaced seals on tank flanges.

I set zero at atmospheric pressure and are now checking zero at 21 bar with -27degrees celcius. but when I opened blocked valves, it gives AL30 and display of level - (minus) levels.
So I understood that, at 21 bar with -27degrees celcius, fill fluid density is cahnged.

But which density of fill fluid will occur.The tank which I replaced diaphraghm seals has -20 to -30 degrees celcius. and its pressure is 21, 22, 23 bar. (between 20 to 24bars)