# Ultrasonic Sensor Interference. Please help!



## Go_snow (Jan 15, 2014)

Little background first. Long ago this forum helped me set up a abb vfd and an ultrasonic level sensor. The vfd controlled a pump that was connected to a tank via a 15ft rubber hose. Level sensor worked great and accomplished what was needed. 

Update to now. We were having suctions issues due to the length of the suction pipe (1000gpm sandy water). So I relocated the pump and connected directly to the tank (8” metal pipe with flanges welded directly to tank). 

Now, level sensor tells me level of water, until I turn the motor on. Then sensor just reads a constant amount and won’t adjust speed of motor whatsoever rendering it useless. I’d imagine this has to do with interference caused by the 50hp motor? What can I do to try to negate this? I even went as far as to order a new sensor and shielded cable. Same result. 

Please help, it’s making our crushing operation suffer!! Thank you! Aj


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## CoolWill (Jan 5, 2019)

Could it be a vibration issue with the sensor? What if you connected the pump with some type of flexible hose or coupling?


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## joebanana (Dec 21, 2010)

But the motor didn't used to interfere with the sensor before the suction issues? What changed? The omission of the rubber hose, and direct connection to the tank? Is the sensor isolated from the tank? Could the motor vibration on the tank have compromised a connection to the sensor? Do you have an output signal from the sensor?


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## Go_snow (Jan 15, 2014)

Problem arose when metal to metal to tank (or proximity of pump to tank). Even if hold sensor over tank with my hand, it will not read correctly when pump is turned on . Driving me insane. Re wired it and checked all connections so I don’t think it’s vibration. The sensor just stops reading and gives a constant distance no matter the level of water (whereas it reads spot on before motor is turned on.


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## dronai (Apr 11, 2011)

Call tech support from who you bought the sensor from.


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## Peewee0413 (Oct 18, 2012)

What sensor are you using, and where are the wires terminated? Near the VFD?

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## Go_snow (Jan 15, 2014)

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/ultrasonic_proximity_sensors/diffuse_1200-1600mm_sensing_ranges/analog_output/uk1d-e2-0a


Just wired directly from abb frequency drive to sensor. I even in hooked the sensor from its mounting locations and brought it inside the control van while still wired. Turned the drive on and sensor behaved as it should inside. Could change height of sensor relative to floor and drive/motor behaved as it should.


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## dronai (Apr 11, 2011)

This may help






About 8 minutes in , it explains how it uses sound for measurment. Possibly the motor moved too close is causing the problem with noise, not vibration


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## pjones (Oct 7, 2019)

Does the issue still occurs if the VFD is set to manual bypass to operate the motor? Setting it to bypass should remove the VFD function from the system and allow you to determine if the issue is VFD caused interference issue or motor related issue. 


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## Go_snow (Jan 15, 2014)

I’ve been running on manual on the vfd (guess you’d call it local), where you select the speed of motor. The sensor still does the same thing when displayed on the screen (level shows correct until motor is turned on to set speed).


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## splatz (May 23, 2015)

I think it's the vibration of motor travelling through the pipe and vibrating the tank, the tank, which disrupts the surface of the water. 

Take a sensor reading with the pump off, and the water still, then bang on the tank with a hammer and observe the reading.


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## gpop (May 14, 2018)

Can you adjust dampening on the sensor?


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## MOA (Mar 12, 2008)

You may have created a ground loop between the motor ground and the 24vdc sensor. The rubber hose that was removed could of acted as isolation between the two. Good luck.


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## Peewee0413 (Oct 18, 2012)

That model is being discontinued. How close are the sensor and wire to the motor while the problem occurs? Tank( if ferrous) and motor properly grounded? If it works fine when you take it away from the motor/tank see if relocating the sensor/cable helps. Try bringing it close to the motor while in your hand and see if it messes up. If you play around long enough you'll find the trigger. Knowing what causes a problem will allow you to eliminate it. Maybe you need a SS housing sensor. Maybe you need a new motor. Good luck 

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## varmit (Apr 19, 2009)

Test the sensor connected to your meter and disconnected from the VFD- with the motor running. If the reading is accurate, you may need an isolator in the analog input. Just because it has always worked before is not really relevant. 

You may need more dampening, in the transmitter, to compensate for the turbulence. Check that the motor and VFD are bonded properly. Recalibrate the transmitter. Is the signal wire shielded? Is the signal shield bonded at one end only? The tank may need a bonding jumper to the piping or building structure also.


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## tmessner (Apr 1, 2013)

Where is the level sensor mounted and what type of sensor is it? If it is a pressure type sensor mounted in the suction line to close to the punmp it is reading the pressure in the suction line which will be lower than the the tank pressure when the pump is running due to the suction on the pump. We had to relocate the sensor on our system to the tank itself to get accurate readings not affercted by the pump.


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## Peewee0413 (Oct 18, 2012)

tmessner said:


> Where is the level sensor mounted and what type of sensor is it? If it is a pressure type sensor mounted in the suction line to close to the punmp it is reading the pressure in the suction line which will be lower than the the tank pressure when the pump is running due to the suction on the pump. We had to relocate the sensor on our system to the tank itself to get accurate readings not affercted by the pump.


Its ultrasonic, posted the link as well.

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## glen1971 (Oct 10, 2012)

What kind of wiring did you use? Is it just #14 or shielded wire? If it's shielded, is the shield isolated at the device? What wiring method was used before to now - hard pipe, flex, etc? 

Is the suction of the pump hard piped directly onto the tank? Is the tank bonded to the same system as the motor? Is the pump bonded? 

What are you reading on your level controller at the VFD? Not the level, but either 0-10 volts, or 4-20 mA, with the motor stopped, and with the motor controlling off the level. Are you seeing a drastic change in the readings?


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## MikeFL (Apr 16, 2016)

Boy I love this website. I'm working on a job right now (in another country) which is going to use ultrasonic sensors to measure distance to move an instrument. Not sure if we can meet the specs we need but when it comes time to figure it out I know who I'm going to ask for advice!

Rock on sparkys!


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## pjones (Oct 7, 2019)

Go_snow said:


> I’ve been running on manual on the vfd (guess you’d call it local), where you select the speed of motor. The sensor still does the same thing when displayed on the screen (level shows correct until motor is turned on to set speed).




My intent with running it on manual bypass was to take the VFD out of the equation. If you are still using the VFD to control the speed then it hasn’t been taken out of the equation. Does your VFD have a bypass function? A bypass that closes a set of contacts to allow the VFD to work as an across the line motor starter? 

I want you to see if this interference is caused by the motor characteristics, or if it is caused by feedback, reflective voltage, line noise, or something else that is inducing interference into the signal cable or sensor by the operation of the VFD. So to do this, you may need to rewrite the motor temporarily in order to get the VFD out of the circuit while you run the motor and see if the problem still exists. 

As others have mentioned, try shielded wire and make sure the shield is only grounded at one end of the cable. Separate the signal wire from the line voltage cables. If the cables have to cross paths do so at 90 Deg angles... standard practices that may have gotten changed by someone over the years. 


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## Go_snow (Jan 15, 2014)

Thanks for the wonderful advice from all. So I switched to shielded wire when I ran into this situation. The sensor is a three wire sensor. So as it stands, I just have the three wires connected from the sensor, to the shielded wire, then to the abb vfd. How to I go about grounding at one end of wire? Sorry as this is all new to me. 
I ran the sensor today. Problems occurred when I moved the sensor within about 2 ft of the motor while running (would place sensor away from motor so vibration isn’t the issue). This also occurred when close to the tank. Got it to read a little bit if I put the sensor about 4’ above the tank, but the readings weren’t great. The motor is grounded to the control van. The pump is grounded to motor through frame, and the tank is hard lined to the pump. Shows that the tank is grounded as well.


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## gpop (May 14, 2018)

There are a few things you can try like making sure the ground for the motor goes to the vfd then run a ground wire from the vfd to the panel but as the vfd is supplying power to the sensor its probably not going to help in this instance. 

You could also try using AO2 on the drive to check if you have a bad channel especially if they welded with the sensor in the tank.



It honestly sounds like you have high frequency resonance in the tank caused by the pump which leaves 2 options

option 1 no guarantee would be something like 
https://www.jmesales.com/proco-prod...MIgPaik72W6AIVjp6fCh0ifANEEAQYASABEgJUYfD_BwE

Option 2 would be to switch to a different type of sensor but that really depends on whats in the tank. If its mainly water i would go with a pressure sensor but if there heavy solids at the bottom (you mentioned sand) then that may be a problem.


p.s One other thing to check is if there is a vortex inside the tank when the pump is running.


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## varmit (Apr 19, 2009)

One end of the instrument shield wire is connected to a good ground. At the non grounded end, the shield is insulated (taped or heat shrink).

If this is a non VFD rated motor, you probably need chokes (ferrite coils) on the VFD outputs. These will help to prevent induced voltage leakage on the motor shaft.

From what you describe above, it appears that there needs to be some bonding installed to tie each piece of the puzzle- pump, tank, piping, motor and VFD to a proper GEC.


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## glen1971 (Oct 10, 2012)

varmit said:


> One end of the instrument shield wire is connected to a good ground. At the non grounded end, the shield is insulated (taped or heat shrink).
> 
> If this is a non VFD rated motor, you probably need chokes (ferrite coils) on the VFD outputs. These will help to prevent induced voltage leakage on the motor shaft.
> 
> From what you describe above, it appears that there needs to be some bonding installed to tie each piece of the puzzle- pump, tank, piping, motor and VFD to a proper GEC.


The guideline I've always used is "no shield in the field". And when we do our QAQC on new installs, I always meter the shield to ground. Guys tell me it's a waste of time. How can I assure the client it is isolated, if I don't test it? Not to mention wasted time later troubleshooting something that is a problem on lazy installs.

A short piece of #6 or a temporary set of booster cables could be a quick test to see if it is part of a bonding issue.


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## Go_snow (Jan 15, 2014)

So I made sure the motor was grounded (have to anyway as required by msha). Then I ran grounding strap between tank and other piece of equipment. Check ohms on tank and found no resistance to ground.


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## dronai (Apr 11, 2011)

You still haven't solved this ?  Wow !


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## CoolWill (Jan 5, 2019)

Physically detatch the sensor from the tank and see if it can read the distance to your hand correctly.


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## gpop (May 14, 2018)

one thing that troubles me is you haven't really tested the sensor to see whats going on in the background. 

Hook a amp meter inline and see what the sensor is doing in ma.


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## gpop (May 14, 2018)

Go_snow said:


> So I made sure the motor was grounded (have to anyway as required by msha). Then I ran grounding strap between tank and other piece of equipment. Check ohms on tank and found no resistance to ground.


Check voltage between the dc+ and dc- to ground in both ac/dc if you find any ac voltage and your meter reads hertz get that reading with the drive on and off. (presuming you are using the drive for 24v power)

most sensors are built to handle 50-60 hertz interference the drive can be programmed to different frequencies (switch freq not speed freq on the 550 its default is 4k parameter 2606 you can try 8k to see if that helps. down side is it may cause the drive to run warmer, lower switch rate will make the motor noisy)

you can also add a little filtering on the drive AI parameter 1506.


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## LARMGUY (Aug 22, 2010)

How to ground a shielded cable










Take the foil and the shield braided cable (called the drain wire) and twist all this together under a ground you have confirmed with an OHM meter. Cut the other end foil and braided shield wire off and either tape it or heat shrink it. I would tape it temporarily. Just make sure there are no accidental connections to the drain or foil to the other connectors.

NOTE: Some manufacturers provide a terminal for and or require the ground be to their communication equipment. Some are separate from the Comms ground, some are the same terminal. Some do not so use a suitable earth ground.


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## glen1971 (Oct 10, 2012)

LARMGUY said:


> How to ground a shielded cable
> 
> Take the foil and the shield braided cable (called the drain wire) and twist all this together under a ground you have confirmed with an OHM meter. Cut the other end foil and braided shield wire off and either tape it or heat shrink it. I would tape it temporarily. Just make sure there are no accidental connections to the drain or foil to the other connectors.


I've never wrapped the foil in with the drain and terminated it. Maybe it's by cable construction, but I was always under the impression it was in intimate contact with the drain throughout the length of the cable.


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## LARMGUY (Aug 22, 2010)

I've done it both ways, I'm just making sure he understands it has to be together electrically.


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## gpop (May 14, 2018)

glen1971 said:


> I've never wrapped the foil in with the drain and terminated it. Maybe it's by cable construction, but I was always under the impression it was in intimate contact with the drain throughout the length of the cable.


same here as the foil is touching the drain it seems a waste of time

I always pull the outer covering away from the cut end then trim the foil and let the covering come back to hide the foil. I then strip 4-5 inches of 16 green and keep the insulation to go over the shield wire. (i hate cabinets full of exposed shields)


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## glen1971 (Oct 10, 2012)

gpop said:


> same here as the foil is touching the drain it seems a waste of time
> 
> I always pull the outer covering away from the cut end then trim the foil and let the covering come back to hide the foil. I then strip 4-5 inches of 16 green and keep the insulation to go over the shield wire. (i hate cabinets full of exposed shields)


When I strip the insulation off of belden or the foil off teck, I use the same measuring device every time to keep it consistent. It's my left index finger, cuz I'm right handed. I run the cut end to the joint on my palm, and have the cut end at my tip. Unless I lop the tip off, it should be fairly consistent. There are some exceptions, depending on terminal lay out, but it works 99.4% of the time, and keeps the shields from touching in the panduit, lacing, etc. Unless it's spec'd, I leave the shields bare, and most specs I've seen are to use clear heat shrink.


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## dronai (Apr 11, 2011)

Update ?


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## Jhellwig (Jun 18, 2014)

Since it is holding a signal once the motor runs tells me it is a noise or vibration thing as that is a common mode of failure on a bad measurement.Most times an electrical issue in an analog signal will cause the signal to jump high or low and be inconsistent. This would be sensitive to speed in the case of a vfd. 

Motors on VFDs make noise in odd sound ranges. This could be interfering with the sensor even though your ear cannot detect it. The surface condition of the water can also effect the reading. As mentioned the mount could be vibrating also. Depending on the kind of sensor you have you might be able to adjust some parameters to account for this. 

One possible solution could be putting the sensor in a stilling well. This will help shield the sensor form some of “noise” possibly causing your issues.


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## bill39 (Sep 4, 2009)

Did you mount the sensor in a “stilling well”. This might take care of any vibration issue.


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## just the cowboy (Sep 4, 2013)

Gone. Amazing how many come for help, we fix it or lead them in the right direction and they go to the land of no return. I am going to change my signature to
" The cost of our answers are not free, we charge you a answer back. DID this fix it??"

Cowboy


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## dronai (Apr 11, 2011)

just the cowboy said:


> Gone. Amazing how many come for help, we fix it or lead them in the right direction and they go to the land of no return. I am going to change my signature to
> " The cost of our answers are not free, we charge you a answer back. DID this fix it??"
> 
> Cowboy


Yeah that would be nice. 

Probably just a noise issue, when he moved it too close. He ruled out vibration.

Was the sensor direct to the Vfd input, no plc ? Wonder why he was controlling speed ? Just a pump


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## gpop (May 14, 2018)

dronai said:


> Was the sensor direct to the Vfd input, no plc ? Wonder why he was controlling speed ? Just a pump


Controlling the tank level no need for a plc when the drive can do it. (probably a remote location from the nearest plc). Add a low level float or inlet pressure switch to the run input and your done.

Judging by the little amount the OP posted its a settlement tank.


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