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Participant

Join Date: Jul 2019
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3051S DP Transmitter Fluctuating

07/10/2019 8:11 AM

Hi,

We have installed Two DP type TX on Air blower - they share common instrument tubing one is HART protocol other is Foundation fieldbus , we are facing issue with HART model ( part#3051S2CD1A2A12A1A)- during normal operation both reading 8000kg/h,

problem : every noon time (13pm-~16pm time ) HART TX start drifting goes 7000 kg/h while in same time FF TX read stable 8000kg/h it's happen daily , we assume it's due to sunlight heat so we covered this both transmitter with insulated sunshade and got improvement in reading but still-this mismatch is leading to shutdown equipment as of it's critical equipment that's why want to eliminate this mismatch problem.

Info : Both TX are DP type and share same tube / same calibration range / only communication difference one is FF other is HART.

any comment please share your thought.

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#1

Re: 3051S DP Transmitter Fluctuating

07/10/2019 1:33 PM

The Hart DP seems to be taking the air density into account by a different calculation....these two transmitters may not be programmed the same...

http://www.validyne.com/blog/application-note-basics-of-air-velocity-pressure-and-flow/

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#2

Re: 3051S DP Transmitter Fluctuating

07/11/2019 5:40 AM

The [Honeywell] 3051 is part of a family of differential pressure transmitters. If connected correctly, the instrument will measure the differential pressure across some sort of restriction in the flow, and <...during normal operation both reading 8000kg/h...> suggests that some sort of algorithm is in use within the instrument to infer flowrate from differential pressure.

<...Air blower...> suggests that the measurement is of pressures slightly above atmospheric.

It ought to be possible and practicable to chase-round the <...instrument tubing..> looking for leaks, particularly if only 1 instrument of the 2 is suspect. If a proprietary leak testing fluid is unavailable, one might use water with a healthy dose of common washing-up liquid in it as the leak will manifest itself as bubbles, which are easily seen. Once found, the remedial action depends upon the nature and the location of the leak.

At these sorts of pressures, a simple kink in the tubing may result in a leak, which the instrument can measure and which cannot be seen or heard above the background din from the <...blower...>. It is likely that any leak will be found on the low pressure side of the suspect transmitter and fairly close to it.

Come back to the forum after this investigation is completed, please.

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#3
In reply to #2

Re: 3051S DP Transmitter Fluctuating

07/11/2019 7:05 AM

the low pressure side the high pressure side

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#4

Re: 3051S DP Transmitter Fluctuating

07/11/2019 7:24 AM
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#5

Re: 3051S DP Transmitter Fluctuating

07/11/2019 7:42 AM
  • If leak elimination doesn't work, the next step is swapping the instruments physically between the two locations, to see if the fault travels with the instrument or remains with the pipework.
  • If the problem travels with the transmitter, try changing-out the suspect transmitter for the stock spare, and try again. It is unlikely to be a similar fault with two transmitters.
  • If that doesn't work then it's a detailed phone call or two with the transmitter supplier and/or manufacturer.

Please come back to the forum once those things are completed.

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#6
In reply to #5

Re: 3051S DP Transmitter Fluctuating

07/11/2019 8:01 AM

Hi,

Thanks for joining discussion about this topic,

Calibration range is 0-100mmh20 for both transmitter and as of primary suspect

HART transmitter just replaced 1 month back ,still behavior is same,

Tubing inspected - no leak - parameter matched for both transmitter - heat exposer parts covered.

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#7
In reply to #6

Re: 3051S DP Transmitter Fluctuating

07/11/2019 12:07 PM

...then it seems a telephone discussion with the supplier is the best route to a solution.

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#8

Re: 3051S DP Transmitter Fluctuating

07/11/2019 3:22 PM

Try swapping the tubing taps to the transmitters if possible.Are the tubes simply joined at a TEE,or a manifold? Could be a restriction in one port getting smaller as temp increases.

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#9
In reply to #8

Re: 3051S DP Transmitter Fluctuating

07/12/2019 7:48 AM

It's connected at TEE,

we may try your option swapping tube but, one thing here I like to share is It starts deviating since noon Temperature rise so now may I need to look this also,

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#10

Re: 3051S DP Transmitter Fluctuating

07/13/2019 10:21 PM

Are you feeding the DP signal into a flow computer with medium (air) temperature and static line pressure compensation?

If not, you're fooling yourselves as to the validity and 'accuracy' of your flow measurements.

The 3051S is a plain-Jane DP transmitter that can provide volumetric flow measurement. It is not a Multivariable transmitter (a multivariable transmitter, the 3051SMV, uses a 4 wire RTD for temperature compensation and an absolute pressure sensor for line pressure compensation).

Using mass flow measurement kg/h units is based an (unwarranted) assumption that line pressure and medium temperature remain constant 24-7/365 AND at design conditions.

Your DP (by itself, without a flow computer) is only capable of volumetric flow measurement. The output of a DP is only valid for the design temperature and design static line pressure. Any thing else is an error (chemistry/physics gas laws).

I suspect that the HART transmitter is actually the one that is reflecting reality better, showing a change in flow rate as the temperature of medium changes. Why isn't the FF transmitter showing volumentric changes with changes in medium temperature? I understand that you want the readings to remain constant, but where in world is air the same temperature hour after hour, day after day, month after month?

If maintaining constant mass flow is critical, then you need instrumentation capable of making an inferred mass flow measurement, not making a volumetric measurement and assuming process conditions are always the same.

Here's graphs of the error due to medium temperature and static line pressure deviation from design conditions:

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#11
In reply to #10

Re: 3051S DP Transmitter Fluctuating

08/10/2019 9:11 AM

Regarding the possibility that the HART transmitter might be reading correctly rather than the FF transmitter, I've experienced that a couple of times except my experience was with temperature sensors (thermocouples). The operators believed the first sensor was correct and complained that the second sensor was defective. A check revealed that the second sensor was good and the first one was defective. Sometimes it's the reading we want to see that seems normal.

A comparison and analysis of the transmitter's parameters might be in order as well as an inspection of the impulse tubing.

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#12

Re: 3051S DP Transmitter Fluctuating

08/10/2019 11:00 AM

Confucius say:"Man with two watches never knows what time it is."

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