We have an application where the level measurement "is done" by a Vegaplus 62 (Non contact Radar), the product is R404A with the data shown below:

* Dielectric constant 7.58
* Process temperature: -48 to 60 °C
* Working Pressure: 22 barg

The Radar is inside a stilling well.

Can anyone tell me if you have had experience with this application, and if you have a cause / solution to this?

 

First of all, you will need to tell us what the "problems" are. Looking at your application parameters, I don't see anything that would cause the Vegapuls to not work. So if it isn't working, you haven't given us enough information to figure out why.

You may be getting phase cancellation from the stilling well. I would probably have used a guided wave radar unit instead, unless the tank environment required non-contact level.

But you have to tell us what it IS doing, and what it should be doing, and what other things are going on, like high rate agitation, frothing, off gassing, etc.

Walt

Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
[email protected]

 

Hello Walt,

Thanks for your prompt response. The thing is that the Radar is completely blind. it measure nothing and also is not possible to calibrate because the changes of level aren't shown. There is no agitation inside, and the surface of level seems quiet... Normally we use the GWR but in this case we bet for the Vega advise because they said that with the data and conditions this equipment will work properly.

Sergio

 

Then there is something they are not seeing. Take the unit out, and aim it at a board or piece of metal that is an exact distance away from the horn. Move the board toward the horn and away from it slowly and watch to see if the "level" changes. Do that until you are satisfied that the unit works correctly outside the tank. Assuming it works outside the tank, then you need to see what inside the tank is blinding the transmitter. It could be a support member, or other internal structure.

Also, what is the dielectric of the material you are measuring the level of? If the dielectric is very low, you may be shooting straight through the material and picking up the bottom of the tank. That would make the unit appear to be blind, too.

Keep us posted about what you find out.

Walt

Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
[email protected]

 

Hello Walt,

We did what you recommended and the transmitters works perfectly. We spoke with the Vega specialist and after they check, they realized that the vapor of this refrigerant absorb the echo even at 2 barg of operation pressure. They are now changing all the instruments with no-cost to a GWR.

In our experience we suggest not to use any Radar Transmitter for Ammonia applications, most of refrigerants, Separators, Steam Generation, Sludge detection among others

Thanks again for your advise, let's keep in touch.

Regards,
SAC

 

Thanks for letting us know what the problem was.

Hopefully this will save someone else from finding out the hard way.

Cheers
Roy

 

All gases have resonant frequencies with respect to electromagnetic waves related to the molecular structure. Most gas resonant frequencies are significantly higher than radar level transmitter frequencies and therefore do not cause any problem.

Ammonia gas resonant frequency is very close to the 24GHz radar operating frequency and thus causes attenuation of the signal. A stilling well helps, but then higher pressure increases the attenuation. This is why you have no signal. TDR or guided wave radar uses a lower frequency and will not have as much attenuation. Another detail to take care about with ammonia is the permeation of the gas through seals which can cause sensor failure.

Tim Little
Product Manager, Radar
Siemens Milltronics Process Instruments Inc.

 

>All gases have resonant frequencies
>with respect to electromagnetic waves

That's very interesting, are there any other gas's that have a similar frequency?
Roy