Krohne Flowmeterproblem

Hi,

I have a problem with a flow measurement.

Could it be that I have a meachanical problem, see the attachment please.

There is a pipe of 50mm connected to a 50mm flow meter and the output is connected to an 80mm's pipe.

Can this be a problem ?

Isn't it so that the preasure decreases at the output when the pipe is larger then the input, that can speed-up the liquidflow ?

Anyone has an idea if that could be the problem, thanks.

You don't say what your problem is but since this is a mag meter you a) better have conductive enough fluid b) no air entrainment c) enough backpressure downstream to keep the flow tube packed when flowing.

the problem

The Problem is that it gives to less pulses to a countermodule.

So the measurement isn't ok. All parameters are okay

Questions...

Are you wired for Active or Passive mode pulse outputs?
What is your scaling for the pulse output?
What mode is the pulse width configured for?
Chances are if you're not exceeding your counter module input max frequency and you have the right pulse amplitude then this will be a pulse width issue. What model PLC and counter module are you sending the pulses into?

The nost common problem with flow meters is improper pipe configuration upstream and downstream of the meter. To give accurate readings the fluid must have a well developed uniform velocity profile. This is best accomplished by having sufficient straight constant diameter pipe upstream and downstream of the meter. Your supplier can give you their reccommendations, but usually 10 diameters upstream and 5 diameters downstream are the minimum. Otherwise you develop eddies and swirls in the flow that distort the measurement.

The expansion in pipe diameter right after your meter is a problem. You don't indicate how much pipe you have between the pump and the meter, but if it is a short distance that is another problem.

Some companies, like Vortab http://www.fluidcomponents.com/ or Canadian Pipeline Accessories http://www.cpacl.com/ make "flow straighteners" that can help compensate for poor installation conditions. Contact them for info, as well as your meter supplier.

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I second what Tom said. The smallest spec. for straight pipe i have ever seen is 5xdia. inlet and 2xdia. outlet. I generally use the 5x and 10x rule in designs as a minimum.


This is a nice document to look at:

http://www.krohne-mar.com/fileadmin/media-lounge/PDF-Download/Magmeters/HB_MID_e.pdf

Hi Combo,
Tom is right. You should have a straight D50 mm of about 400 mm to 500 mm before the flowmeter, and the same after the flowmeter, and only than you can increase the D to 80mm if it is necessary.

To clarify & stop others form going off in different directions;
Does the Flowmeter display (if it has one) indicate proper flow indications i.e. rate & totalization? If there is no display, does a HART communicator or laptop indicate proper flow measurement? If you are measuring flow accurately then you do have, as I stated earlier, a pulse signal to input module issue. Granted, all the other posts are valid for flow conditioning considerations but let's clarify your situation.