Ultrasonic level distrubances

[djs]

I have an ultrasonic level measuring system that consists of two transducers mounted in a wastewater wetwell, each connected to it's own transmitter. We are getting occasional distrubances similiar to that shown on the attched file. The signal ramps up linearly for about 15 minutes and then ramps down in three minutes. I would like suggestions as to what is causing these distrubances. The occur very infrequently, maybe once a day or every two days.

 

[controlnovice]

-self testing

-Outside interference: device/xmtr proximity to other equipment, wiring/signal interference with other equipment (what else runs during this time?) Could be something located elsewhere whose wiring ends up in JB or conduit with this signal. Is wiring shielded and grounded properly?

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This is normally the space where people post something insightful.

 

[danw2]

Why would you think that it is not a real level change? My money's on a real change. Who's gone out there to visually inspect at 10PM?

On the long shot that it's not a real change, it might be that the sonic pings are periodically intefering with one another and alias just so that it appears as you see it on the trend chart. The interference period is whatever day's long duration it takes to get the pings just in synch enough to effect one another.

Milltronics ultrasonics had a 'synch' signal to make sure the one transducer didn't interfere with another.

 

[djs]

Controlnovice: I failed to mention that the transmitters are connected via a fieldbus. No loss of comms, and no analog noise. Still could be an interferenc on the transducer signal line.

Danw2: We have joked that it is from a plant operator going inot the wetwell to take a nap. However the WW is closed, the influent is a 24" pipe and the effluent is via pumps which would choke on a 6" object. And yes we have looked in the WW and there is no floating 6 foot tall object. We have connected the syncs together for the two instruments and will see how it works over the holiday.

Millitronics tech support thought it might be foam that is delaying the US pulse. I don't know, seems somewhat far fetched. If we still have the issue over the weekend, we will be installing a temporary transducer in a different location to replace the current one that is malfunctioning.

 

[danw2]

I was wondering about it being an operator myself. . .

The really old Milltronics used an external temperature sensor, necessary because the speed of sound changes with temperature. The recent ones (last 8-10 years?) have integrated the temp sensor into the ultrasonic transducer.

Any chance an external temp sensor is going wacky?

What's so unusual is the nearly linear change. I can't imagine how interference could rise and fall in such a linear fashion. Do you know what the speed of response is? Could it be a filtered/damped step change? I seem to recall that on some models, the speed of response up and speed of response down is set independently, which might account for slow rise slope and faster fall slope. Which still doesn't account for the step change in the first place.

Has either transducer been removed/replaced recently? Overtightening the NPT mounting threads is known to make the transducer wacky.

 

[hacksaw]

looks like an inflow surge with the pump controls responding normally

suspect that your xmtrs are working just fine.

see if you can better quantify what is going on flow wise

 

[controlnovice]

We're slowly getting rid of our Milltronics and replacing with another manufacturer. Have had horrible results with Milltronics, and the support in our area is not any better.

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This is normally the space where people post something insightful.

 

[djs]

Last Friday we connected the syncs of the two transmitters together. Since then (today is Thursday) there have been no distrubances. Looks like the sync fixed it.

 

[Chinook82]

I'm surprised about Milltronics, I thought they were the leaders according to Control Magazine?

 

[IRstuff]

You stated that there were two transducers; are both showing this effect, or only the -01 sensor? Are they supposed to be showing the same information?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[djs]

The system consists of two independent transducers and transmitters, one transducer to a transmitter. Both transducers are mounted in the same wetwell. Both should read more or lees the same level taking into account floating objects.

With the syncs connected more than three weeks without an event. The distrubance almost always occured on transducer 1. And always occured on transmitter 1.

 

[IRstuff]

So, obviously, either transducer 1 or transmitter 1 or both have a problem. The next obvious step is to mix and match to see where the problem moves to, if it moves at all. It seems to me that you've spent a lot of time dancing around the need to replace either or both.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[djs]

We did all of that. What solved the problem was connecting the syncs between the two transmitters.

 

[wfsymon]

hey,
the Sensors is it working well now,
mainly these sensors will do the self check as per the programmed regular interval.

the best way is to sawp and check it,as the sensor and transmitter may have the issues.


sym.