Differential level across screen by ultrasonic sensors

W

Thread Starter

Wasif Sadi

Hub Power Plant, Pakistan is a 1200MW thermal power station. We want to measure differential level across our travelling band filters to monitor the condition of the filters and control the speed accordingly. These screens are installed at sea water intake and previously installed bubbler system does not work properly. Now we want to install non-contact type (Ultrasonic) sensors to monitor differential level across screens. We will appreciate if somebody who is already using ultrasonic sensors for such application share his/her experience with us. What make of sensors and transmitters are used and how they are performing?

THANKS
 
C

Curt Wuollet

Are there ultrasonic pressure transducers? It sounds like you want to measure differential pressure. Doesn't sound like appropriate technology to me.

Regards
cww
 
W
Actually, Curt, it is. Milltronics (now Siemens) has been making a differential ultrasonic level transmitter/controller for gate and travelling screen filters for probably 20 years. It uses two transducers, one on the upstream and one on the downstream side of the
gate, and performs the programmed control action when the differential level reaches the preset limit.

I know Siemens makes one. I dunno who else.

You can clearly do the same thing with a PLC and two separate ultrasonic level transmitters, but you program the control states.

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C

Curt Wuollet

My bad, I misunderstood what he was trying to accomplish.
What with bubblers and all, it sounded like a dp measurement.

And it probably could be done that way. Which would take
care of any surface action. Forget I said anything.

Regards
cww
 
Curt
You didn't misunderstand "it is a DP measurement, using a DP cell or ultrasonic's the result and physics are the same".

I have found many installations using the bubbler system with DP cells, but to improve their reliability it is necessary to add other instruments to ensure blockage, lack of pressure, power failure etc do not cause a problem.

The major problem is that high differentials can cause the screen to lose it's footing and move down the channel essentially shutting down the process and costing allot of money.

As a result I specify differential ultrasonic level detection as a replacement to DP devices (cost effective, no extra instruments and can be made redundant etc).

Dennis
 
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Curt Wuollet

What level are you measuring? A standpipe on each side? I guess that's what I didn't understand as ultrasonics don't normally measure pressure directly. I was thinking that shooting the surface level on each side would have a
number of problems as well. But with stilling wells or standpipes, it all makes sense :^)

Regards
cww
 
You can try an Endres + Hauser product, Prosonic FMU 862, a two-channel version which could simulataneously measure the upstream and downstream levels. We have been using it for our fine screens' and mechanical coarse screens' automatic operation.
 
Curt

It is a stilling well on each side of the screen (8 inch PVC seems to work fine). Although the fluid is relatively calm, without foaming and the intake from the source is submerged, surges can still take place (these are not a problem with the correct dampening in the instrument).

The stilling wells act as a collimator for the ultrasonic signal and removes the nasty ladders, pipes, columns, etc. from the reflection path.

The bubbler system infers the level from pressure and the ultrasonic measures it directly, it is not the absolute level that is the problem it is the differential level which can be equated to a force load on the screen causing a potential problem.

Dennis
 
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