Hi,

We have purchased some vortex shedding flow meters for air stream and the calibration certificates along with the instruments indicate they have been calibrated with water!

I can understand the water can be used for calibration of flow meters for different liquids but not for the gases.

The supplier claims, vortex flow meters are calibrated with water only as a standard engineering practice, even if the intended media is gas.

Is the above statement correct? What is the standard/reference to accept or reject this claim?

Thanks,
Hamid

 

If you did not specify calibration on the correct fluid, what you get is the factory standard calibration...which in this case is obviously water. If you knew they were to be used on air, and you wanted cal certificates on air, and you did not specify that in your order, you can send them back to be calibrated on air...but it isn't going to be no charge.

This is an object lesson. You aren't wrong, and neither is your vendor. Your vendor gave you exactly what you asked for, which is what they are supposed to do. Vendors who give customers what the vendor thinks the customer really wants but didn't ask for often get burned.

So, what do you do now?

Put one in and see how it works, put them all in, and trust that they are accurate, send them back for factory cal on air, or find a local cal lab and have them check the calibration on one of the meters, and use it as a master meter to calibrate the rest of them...or a combination of those things.

My bet is they will work fine with the water calibration.

Good luck,

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
Mailto:wboyes [at] putman.net
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

 

It is quite usual for some gas flow meter types to be water calibrated or calibration checked. It is especially true for large sizes where suitable gas calibration facilities are not available and especially so when high pressures are involved.

Low pressure gas calibration is often quite feasible using bell provers or even, for very low flows, soap bubble methods.

Water calibration is typical for gas turbine flow meters. gas calibration could be time consuming and very expensive.

Thus it is not unusual to derive a proxy relationship between water and gas calibration through original research because it is very easy to use water as a safe calibration fluid over a very wide flow rate range.

Note that turbines and vortex meters are velocity meters. Vortex shedding is a function of the viscosity at the edge of the bluff body and thus volumetric flow is a function of the velocity and the blockage ratio. Vortex meter calibration is very predictable if they have been manufactured with minimal variance and a proxy calibration should be even more reliable than for a turbine meter.

Other examples are orifice plate meters and domestic water meters which are neither of them calibrated but the water meters may be quality checked by flowing water through at different flow rates and testing that the results are within certain set limits (often much tighter limits than the meter accuracy would suggest).

The early Neptune vortex meters whether used for liquids gases or steam were all manufactured with a common meter factor for the duty.
This is because the old style electronics required the meter factor was programmed using solder links.

So the meters were not actually calibrated but calibration checked (checking that the common meter factor results in the expected accuracy).

Today you should find that the individual calibration (which involves determining unique meter factors for each meter) of such meters will give better results than the class accuracy of the Neptune's which was +/- 1%.

So what you can do and should do is go back to the manufacturer and ask them to explain there calibration procedures to you and if necessary ask for any technical data to substantiate heir water calibration. This is cheaper than a gas calibration.

 

Vortex shedding is a function of the <i><b>viscosity </b></i> at the edge of the bluff body and thus volumetric flow is..........

Should read:

Vortex shedding is a function of the <i><b>velocity </b></i> at the edge of the bluff body and thus....

Sorry.

 

I know you can calibrate the Yokogawa DYA vortex flow transmitters with a frequency generator.

Mike

 

I think what you mean is, the electronics module of the Flow meter in question can be checked. Calibration involves checking the "obstruction" that produces vortices, the vortex pickup electronics head, the actual converter and the final display (whatever type is in use).

If calibration needs to be checked, it will need to be compared with a standard meter or inside a prover loop.

Regards,
Tomy Zacharia

 

Hi,

What is more important is to know the accuracy that you expect from this meter, the accuracy actually will determine whether the meter calibrated on water will meet your requirement or you should do air calibration as your service is gas wherein you will get much better results as compared to water calibration.

 

Hello Amid

vortex is a velocity meter. The K factor determined with water, is valid for ANY fluid: steam, air, or liquids. (at least in the 99% of the applications)

So, for the manufactures the simple way it is calibrate with water.

The differences will be the minimum and maximum flow you can measure in each fluid, because this depends of Reynolds Nr. of the measured fluid (and Reynolds Nr. is a function of density, viscosity, etc.)

In a few words: you can use your water-calibrated vortex without problems, but ask the vendor to inform you the limits of the measuring range.

 

each vortex flow meter is sized-up using a sizing software. from there you can specify the medium in which the flow meter will be used. it will provide you the K-factor of meter factor for your particular application. it changes depending on the medium. so if you try to use the meter with a different medium. you must re-size your meter to obtain a different K-factor. you can then input it to your meter. also, other parameter will change if you change your medium so you have to change every parameters inside your meter.

 

how to convert the flow of water to nitrogen. Calibration certificate is given for water, now i want to convert the flow of water to nitrogen.