DP Level Transmitter Showing Error of About 20%

<...Is it possible that the LRV and URV can be defelected by using the wakie-takie or mobile near it?...>

Yes, it is possible.

<...how can I rectify the same...>

Turn the damn things off and take them away immediately, especially if the liquid is flammable and neither is EEx-rated!

When was the last time the equipment was set-up on an instrument technician's bench? What does the calibration record say, and what has changed since then?

1) For a level application, the DP transmitter is probably showing pressure in mm or meters of water column.

The transmitter has no mean of correcting for specific gravity (SG) of the liquid being measured. The SG correction is done at the receiver device: indicator, controller, recorder, PLC, DCS, whatever.

If the error is a consistent 20% error, is the error due to the SG being 20% different than that of water (SG =1.000)? If so, the transmitter is working as it should. Make the SG correction at the receiver.

2) An error due to radio interference, particularly hand held radios, would likely not be a constant error, it would be an intermittent error and it would like vary in amplitude; it would likely not be a consistent 20% error. Testing for a radio error is easy. If the error comes when the radio is keyed and disappears when the radio is turned off, then it is due to radio interference.

3) If your HART communicator is not working, how do you know what the LRV and URV settings for the 4-20mA output are?

thanks Mr. Iris for ur valuable info, the unit is in MM, as a fluid i am using Condensate (SG: 0.8), HART Communicator presently not working it is gone for service. But at the time of installation it is working and we set according to 4-20 ma. the level sensor is working good before 1 week. but now a time it is showing error of 20%. so pls tell how I rectify this dam thing.

If the error is constant across entire range,the problem is a Zero adjust error.If the error increases or decreases with signal level, the problem is a Span error.

Is error 20% high, or low?

How are you equalizing the HI-Low sides of the DP? Improper sequencing of the equalizer/isolation valves can result in blowing condensate out of the low side leg, and give inaccurate readings.If not,check the series resistor (250 ohm?) at the end of line, it may have changed value.

Asifidrsi,

No have field communicator (HART) is a problem nowdays

But you can do this,

Using a portable calibrator or fluke 744 plus the pressure module apply the pressure to the pressure port(transmitter) in mm of water equivalents to both zero(LRV) and span(URV) values and check the mA output.

If you see that something is wrong with the range, use de buttons ubicated in the top of the housing in the case for rosemount transmitters in order to fix the ranges according the data sheet or your calculus regarding the SG

Please, can you show us a drawing with the vessel and the SG.

I think that the Specific Gravity of the liquid has changed

Regards

JP

Yo Asif

When I see an error in instrumentation of 20 %

then is the first thing on my mind : an error between the settings

0-20 Ma or 4-20 Ma , that's a difference of 20%.

check your level transmitter / inputcard

T L.

There might be level instruments that are 4 wire that can be ranged 0-20mA, but I assumed a 2 wire, loop powered level transmitter with a 4-20mA output.

If the wrong input scale (0-20mA) is used with a 4-20mA transmitter, then the error will not be consistent over the span.

A transmitter ranged 4-20mA with the receiver ranged 0-20mA will show a 20% error at zero, but the error will taper down to 0% error at full scale. The claimed 20% error will only occur when level = zero, which might be the case.

At a level of 50%, 12mA (on 4-20mA) will show up as 60%, a +10% error on a 0-20mA input.

Of course, with no HART communicator, every setting is up for grabs.

Check earthing connections

You said you are measuring condensate with sp.gr of 0.8.

I am assuming it is steam condensate.

The condensate has to be at around 476 Deg f to have a specific gravity of 0.8.

The transmitter can not withstand this temperature and the static liquid in both the legs will be close to ambient temp .and hense filled with liquid sp.gr of 1.0 .

The span of the transmitter may be correct based on sp gr of 0.8,but if you assumed the static legs are also filled with sp. gr of 0.8 then the zero would be shifted 20%(1-0.8=0.2)

So thru out the reading the level would be off 20%

Theoretically, a the signal coming from a mobile phone or any device generating analog signal can interfere or affect your values from your transmitter but only at the instant a call was made after that there will be no interference expected. Regarding the 20% error, it's really a big discrepancy. If your using wet leg application for your dp, one possible source of the error is when the amount/volume of your seal liquid (water, glycol, etc.) is lessened due to leak or vaporation. This will give you unprecised level measurement based on the computation for a dp application. If your using a dry leg system, the error may be associated to condensate on the low port side of your transmitter. Try also to check the accuracy of your transmitter, do a five point calibration. If your transmitter is working well maybe the above reasons are enough for you to rectify the error.