What signal type is the probe? Thermocouple, mV/V, 0-5V, 0-10V, 4-20mA, PWM? A more robust signal type will help eliminate noise. Otherwise, if you can identify the frequencies of the noise, a filter can be applied.

If the problem truly only occurs when probe is in water, then maybe you are using a grounded tip thermocouple and you have a ground somewhere else in the circuit... and the water is conducting?

You can get ungrounded tip thermocouples. They have a slower response time.

RTD tends to be less susceptible to EMI than T/C in general. It's not clear your problem is necessarily related to EMI.

Just my thoughts fwiw. I'm not a big instrument guy.

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(2B)+(2B)' ?

Electricpete touches on my first thought - is this a grounded tip thermocouple? In this case it may be a few microamps of stray parasitic current.

My second thought is that ferrite rings for your VFD will probably not work. Most magnetic materials saturate easily with current.

My third though is to use a ferrite on your probe. A toroid with ID sufficient to pass the probe wire through 3 or 4 times. That may deter the EMI signal from traveling on the probe cable. Possibly quick and easy.

With it in the water stop the VFD and see if the noise stops. I've heard nothing that shows they're related yet.

Keith Cress
kcress - http://www.flaminsystems.com

To answer some of the questions,

The temp probe has an Rj11 connection and I believe its a thermocouple

I have ordered a ferrite ring to try on the probe

If I turn the VFD off the noise stops

Not sure if this information helps, but the water is saltwater not fresh.

It sounds like a conduction issue to me as well. As mentioned already, a setup that insulates the probe/wires from the water would likely solve the issue.

@LinelHutz - This may be a dumb question, but the probe is designed to be in water. How would I go about insulating it more from the water?

I believe you're talking about the grey wire with the red end? I'm not sure what the red is, but it looks like tape or heat shrink which might not be that good at sealing and insulating what's inside from the outside.

I would expect to use something more like this for an industrial type of use.

https://www.iothrifty.com/products/transition-join...

Unfortunately, I'm stuck using the type of probe, otherwise I would try something else. I plugged in another probe I had and got the same results. I would be surprised if they are both defective. Also, I've used these probes elsewhere on site and not had this issue.


Here is a close up, it's seems like they dip it in some kind of rubber

For some extra info, this is how things look when the VFD is off but the probe is still in the water

What is the sampling rate. Those are remarkably linear changes and look more like it's undersampled and there is a high-resistance short circuit somewhere, though the one spike down is farther than the rest, so it's not helpfully constant.

Is there a thermostatically controlled heater?

I see it as,
1. Noise directly conducted into the probe as most likely
2. Some kind of AC voltage in the water that is inducing noise into the probe. I'd think the voltage required for this would be felt if you stuck your hand into the water.

I still don't know what type of probe that is (does anyone recognize it?).

But interesting to see the rubber coating suggests an attempt to exclude moisture. But looking at the first post photo it looks like the probe is submerged past the level of the rubber so that the grey cable (twisted shielded pair instrument cable I think) is also submerged. That would defeat the waterproofing of the rubber I'd suspect you may have potential point for water entry into the circuit either at the interface or maybe even through the grey cable. That could also potentially explain why you only see the problem when the probe is submerged (although tbh I'd think if moisture got in the problem would not go away as soon as you remove from the liquid... it might take awhile to dry).

Can you hold the probe higher in the liquid so only the rubber part is submerged? (that would help prevent moisture entry if it's happening).

Also to check for moisture entry electrically, you could lift leads at the other end and megger instrument leads to shield, leads to ground, and shield to ground. Perhaps do it with probe/cable deep in the liquid as in first photo, although you'd want to give some thought to whether such test could itself cause damage when meggering a potentially damp circuit depending on test voltage used. I'd start with low voltage like 100vdc and stop if I see bad results or work my way up in voltage if I see good results... I think instrument cable/sensors can typically be meggered to 250vdc or even 500vdc but you might want to double check that (the unknown mystery sensor adds small additional uncertainty).

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(2B)+(2B)' ?

>this is how things look when the VFD is off but the probe is still in the water (chart 3 posts up from here).
So when the VFD is off you still see downspikes as shown on the left side of the chart, 8:20 through 8:55, correct?

Observation: Sampling rate - Looking carefully between 8:40 and 8:50 you can see that it's one sample per minute.

Is the data collector (whatever the probe plugs into) battery powered or line powered?

Can you use another temp sensor/indicator? Can you borrow a battery powered DVM with a temperature input and try a 2nd device to see if it mimics this behavior?

Can you tell us what the temp sensor/indicator brand/model is?

What is the process the photo shows? Why is there open water? Is the water heated/cooled? Is it a plating bath? (room cleanliness tells me no, but I have to ask). Is the water superconductive, like coming off a softener regeneration cycle? Why is there so much PVC around and so little Sch80?

He wrote it was saltwater, so some guess work, agriculture near the Atlantic, fish tank, akvarium?
+20 C maybe a bit high in temperatur for sea living creatures but works for many too.
Not sure what can be grown in a saltwater tanks, seaweed maybe.

Maybe putting the probe and all of the cable in a separate smaller submerged plastictank in the big one with fresh water in it, would help.

BR A

@3DDave - I'm in the process of setting up a plate heat exchanger that using a different temp probe to maintain the correct temp in the system. Currently it's not up and running. The sample rate is every 2 seconds.

@Electricpete - the probe is made by avtech, they don't have the exact ones listed on the website as these are slightly customized. I have the same probe elsewhere, in other systems, fully submerged in water and don't have this issue. I can certainly try having the probe higher up in the water column.

@Danw2, Apologies I wasn't very clear, the down spikes occurred when the VFD was on, the straight line is after it is turned off. I should have annotated the graph! The data collector is line powered, but can run off an internal battery. I don't have another temp sensor I can try at the moment. Temp sensor and data collector is an Avtech. The system is for growing fish! Thus the reason for so much sch40 pvc.

Confused; Do you have a digital multimeter and if you do do you know how to use it?

If you do, set it to AC auto or 200+ volts. Plug a grounded three terminal extension cord into a nearby outlet.

Using the meter and standing within arms-reach of the water.

Put one probe in the extension cord ground hole.
Put the other probe in the narrow extension cord slot.

You should see a reading of about 120Vac on the meter.

If you do, pull the probe out of the slot on the extension cord and without moving AT ALL the probe still in the extension cord ground hole dip the tip of the other probe into to the water.

What reading do you get?

Try it with the motor running and not running.

Keith Cress
kcress - http://www.flaminsystems.com

As a comparison, this is the graph produced by the same type of probe, submerged in the same way, in another system. The only difference is, there isn't a VFD in the room with the probe.

Itsmoked - I do have a multimeter, I can just about use it. I will give it a go when I get back to work.

I would say defective probe since you have the same ones working underwater in other places. Swap the probes and see if the problem goes with the probe or stays with the VFD.

PT100 is a time tested reliable probe with linear resistance characteristics for temperatures up to 200 deg C in case you are looking for an alternative.

Muthu
www.edison.co.in

> @Electricpete - the probe is made by avtech, they don't have the exact ones listed on the website as these are slightly customized. I have the same probe elsewhere, in other systems, fully submerged in water and don't have this issue. I can certainly try having the probe higher up in the water column.

Yes I would recommend trying that. You can continue to troubleshoot vfd as a source, that may well be it. But I would not rule out water intrusion just because you have another one working fine without vfd. Water's ability to penetrate into circuits is not necessarily predictable / repeatable. We have many outdoor instrumentation circuits (not submerged but damp) and every once in awhile we get a problem on one of them traced to moisture. They don't all fritz out at the same time.

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(2B)+(2B)' ?

Freshwater is dimagnetic repels magnetism, while saltwater do not.
It would be a easy test putting the probe in a glas bottle with freshwater just holding it in the tank to see if it makes any difference.
And I am a bit curious of the result.

It's also important that the motor and pump is properly potentially grounded.
This is not the same as protective earth PE.
Since most of the equipment is plastic this might not be so and that the motor cables are shield and connected to the bonding circuits.
The red square is the inverter.



Best Regards A



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Redsnake has a good idea. Use fresh water in a bottle with the probe inside as a test. This will insulate from any stray DC or low frequency current to the probe.
Don't use salt water in the bottle or the bottle will be more like a capacitor to the tank water. A rough estimate of a 3" dia bottle 5" deep filled with salt water in the salt water tank is around 700 pF. Stray VFD switching currents of 100 kHz or higher will not be attenuated much by this capacitance.

Edison123 - I actually bought a new probe as I thought this might be the issue, however, the new probe acts in the same way.

Redsnake - I had to drain the tank to do some work on the system. As soon as I get the tank refilled and the system running. I will test out the probe in a glass jar of freshwater and update you with the results.

I will update in a few days. Hopefully, this can get solved.

I think I found your probe here (photo below). Three observations:

1 - It talks about "ambient temperature" measurement, which to me means air temperature, not liquid temperature. They mention silicon coating to protect it from the elements, ok that's good but to me it's still not the same as saying this thing is designed for immersion.

2 - It looks like it terminates in a telephone jack. Maybe it's telephone cable? We certainly don't have any instrument circuits like that at our plant. From my understanding most instruments should typically be twisted shielded pair for noise immunity, I think phone cable is just a twisted pair. That could be another problem. Maybe try making sure that cable is not routed close to any power circuits/equipment. (is anyone else familiar with this type of cable and whether it is suitable for instruments?)

3 - it's called a digital temperature sensor. I don't really know what that means, it's as if they're suggesting there might be some digital circuits inside that cylinder with digital signal in the cable. All I'm familiar with is RTD's and thermocouples with analog signal in the cable.



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(2B)+(2B)' ?

Nice sleuthing Pete!

Keith Cress
kcress - http://www.flaminsystems.com

Flat phone cable is not twisted. This allows it to be used with those small crimp connectors. RJ 5?? Memory fails.

Certainly "outdoors" is not "submerged in salt water" though it might outperform it's target application.

> For some extra info, this is how things look when the VFD is off but the probe is still in the water

The plot shows spikes and then constant temperature. Are you saying:

• 1 - the vfd was off the whole time


or
• 2 - the the vfd was turned off during the middle of the plot (spikes before turnoff, no spikes after turnoff)

.

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(2B)+(2B)' ?

Electricpete - The VFD was only turned off after the temp reading returned to normal

3DDave - It's a RJ11 connection. The wire used is alpha wire, type 78104

The shape of it makes me think it's a Dallas DS18B20 sensor like this.

https://www.robotshop.com/ca/en/ds18b20-waterproof...

Quote (veryconfused)

For some extra info, this is how things look when the VFD is off but the probe is still in the water[/quote[

Quote (electricpete)

The plot shows spikes and then constant temperature. Are you saying:
1 - the vfd was off the whole time

or

2 - the the vfd was turned off during the middle of the plot (spikes before turnoff, no spikes after turnoff)

Quote (veryconfused)

The VFD was only turned off after the temp reading returned to normal

thanks. It's an important answer and I want to make sure we understand exactly what you're saying. Is it scenario 1 or scenario 2?

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(2B)+(2B)' ?

I turned the VFD off around 09:00. So spikes before turnoff, no spikes after.

ok, that clears it up nicely. Sorry for being dense. That definitely steers us towards vfd noise rather than towards moisture.

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(2B)+(2B)' ?

So from Lionel's link and the telephone wire I guess it's a digital serial connection.

Maybe move the probe and telephone cable further from motor and any power cable.
The 2nd photo showing some panels on the wall, that is all power and vfd control, right? I sure hope the temperature digital signal cable (telephone wire) doesn't go anywhere near there.
Where does that temperature digital signal cable go? I would trace it back to whatever digital unit it connects to and look for where it might be close to power circuits. Is it the same computer unit as the others that are working fine or is it a unique unit? (if unique unit then expand your search for things that may be interacting with that unique unit and its grounding).
It does occur to me that serial communication sometimes includes data integrity checks like a parity bit. There might be something that could be done on the software side to discard corrupted data if you talk to your vendor. (although with so many jumps down to exactly 10 degrees, I wonder if that is the default value it goes to when it senses "bad data")

I'm getting far out of my depth though. I'm not an instrument guy and that goes double for digital instruments... I blame it on my employer and their glacial speed of adopting new technologies.

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(2B)+(2B)' ?

Early in the thread he wrote that the spikes disappeared when he took the probe out of the water.
If the interference had come from the probe cable being to close to the power cable to the motor and especially if it wasn't screened the spikes would still be there even if the probe is in the air.
I think we can exclude that one.

And the Avtech "telefon" cable does not look exactly as his, the one on his probe looks more round.
He wrote that it was a Alfa wire 78104 it looks like this.



Moving the probe further from the motor might help, as you suggest.

Best Regard A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Quote (veryconfused)

Unfortunately, I'm stuck using the type of probe, otherwise I would try something else.

Why is this?
Is it a complet system?
There still must be a brand or something either for this probe or the system that evaluates it or some other data.
Most machines follow some kind of standard, so that there would be only one probe that would work for this seems unlikely.
If it is not a one of a kind system.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

RedSnake - I'd be willing to try another shielded digital temp probe that I can connect with a RJ11 connector. I wouldn't know where to look to find one. You can certainly hook up other probes not made by avtech to this system. Most of the probes I connect to the avtech unit are not made by avtech.

electricpete - The digital temp cable doesn't run anywhere near the power for the VFD. It's in its own conduit, well away from it. I can send more photos when I get back to work. I may even have some on my phone. I have other avtech units in other rooms, all using similar probes.

Probably not the VFD. Probably from whatever the VFD operates.

> He wrote that it was a Alfa wire 78104 it looks like this

ok, good that looks a lot better than telephone wire.

> If the interference had come from the probe cable being to close to the power cable to the motor and especially if it wasn't screened the spikes would still be there even if the probe is in the air.

Yeah I forgot about that. I can believe capacitive coupling on the high frequency components. Water has a dielectric constant about 80 so it gives much better capacitive coupling in water than air. I'm not sure if the salt makes a big difference unless we are suspecting resistive coupling which doesn't seem as likely to me but who knows. I don't think it affects the next steps which one we suspect.

We talked about moving the probe further, that's good.

We talked about moving the probe up so only portion of probe is submerged. I think that's good although I don't know how much of the probe needs to be submerged for accurate temperature sensing of a liquid (and OEM might not know either because it's not a liquid temperature sensor). At a minimum get all of that cable out of the water as much as possible since there can be capacitive coupling to the cable too, which would be minimized by getting it out of the water.

Some other things were mentioned to try to reduce emissions from the equipment.

Beyond that the solution that comes to my simple (non instrument guy) mind would be put progressives trial and error involving shielding by grounded structures. move probe close to a large existing ground plane. put a grounded barrier between the suspected source (the motor) and the probe/submerged cable. If that didn't work maybe try enclosing the probe / cable in something like a grounded can with enough openings to allow flow for temperature sensing. It might slow down your temperature response a bit but from your plots it looks like the system temperature doesn't change very quickly so that might not be an issue. It's admittedly a messy nonstandard solution idea but worth at least as much as you paid for it

I guess from all the discussion it's logical the motor is submerged but I wanted to verify that. Is it some kind of submersible motor? Is it that cylinder in the first photo the motor? What does the motor drive... a pump?

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(2B)+(2B)' ?

We still don't know if that saltwater is energized or not. It could be lethal.

Keith Cress
kcress - http://www.flaminsystems.com

Electricpete - No submersible pump. This is the location of the pump that is connected to the VFD. I will try a grounded can or something around the probe to see if that helps.

I did drop in some stainless steel rods into the sump and grounded those, however, that didn't help. I wonder if moving the probe closer to the grounded rods might help. I will try that.

of the main pump that runs of the VFD.

Are the pipe passages on the pictures the same ones from the outside and from the inside.



And what is this ??


Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

The pipe passage you can see below the temp probe is for another pump, not pictured. That pump is not on a VFD and has not been running at all

The black thing, is a drum filter. https://hexfilter.com/

Okey is the probe that you are having problems with near this drum filter or does the tank with the VFD drive not have one of those?

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Wow that's weird for the pump/motor outside the tank seemingly influencing water which seems to be influencing probe inside the tank.

I guess we have to suspect (?) that high frequency seen on the stator is either conducted direct to pump casing from stator frame or else it is coupled from motor stator to motor rotor which in turn might have some kind of electrical connection to the pump impeller. (do you happen to know the coupling type).

Under that theory, to my simple thinking, the highest magnitude of this HF voltage-with-respect to ground would be highest at the pump (casing or impeller) and voltage would taper towards 0 everywhere that you have a good ground. The more well grounded surfaces it has to go past before getting to probe the better.

Is the tank itself grounded? It seems like it should be. I like the idea of putting a can around the probe. If you can't do that I might be tempted to try grounding suction and discharge flanges associated with this pump, either directly at the pump or where they penetrate the tank. I guess flat braided style groundstrap for high frequency would be best if you have something like that, but I wouldn't let that stop me from trying whatever I had available.

If you're inclined toward troubleshooting maybe put a meter to check resistance to ground from tank (if it's a metal painted tank you have to find access to unpainted area). And check resistance from ground to pump flange (easy access there, no paint). It would be even more interesting to see if you can find evidence of induced voltage on the pump flanges. A a voltmeter to ground in total rms mode would be a start (would include high frequency as well as lower frequencies).

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(2B)+(2B)' ?

Redsnake - yes, the probe is near the drum filter. I’m not quite sure what you mean with the second part of your question.

Electricpete - not sure what you mean by coupling type. You need to dumb things down for me.
The tank itself isn’t grounded. I did bundle some stainless pipe together and put it in the sump which I grounded. If that’s what you mean?

The tank is made of fiberglass. The only metal parts are the pump and motor and the bolts for the flanges

I will try out some of the things you have suggested later this week.

I was wondering if the the motor with VFD drive is supplying the same tank that has the drum filter?
And that is the tank where the probe problem is.
And this drum filter is powered with a ordinary motor I suspect.

Electricpete, i think the VFD drive induces a magnet field around the motor this electric field can damage the bearings in a motor if they are not made for this type of application, which is a whole other discussion.
This induced magnetic field will fluctuate with the VFDs regulation of the motor.
Since the motor are mechanically connected to the pump that is also made of iron the magnetic field will also expand on to the pump.
And since salt water are better at transmitting magnetic fields then fresh water that are dimagnetic (repelling magnetic fields) I think that it is possible that this is the source of the disturbances.
It might even be possible that the magnetic field might go through the glasfiber tank and get in that way.

You know this test pens AC Voltage Detector that is used for finding cables inside walls with a lamp that lits up.

veryconfused if you can get your hands on one of those you might be able to see how fare the magnetic field can reach.



If I am right it will not help containing the probe in something that can be magnetized.

This is me half WAG = wild-ass-guessing.

Best Regards Anna

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Silicone is highly permeable to water and water vapor. Not a very good choice for submersion. Putting the probe into a stainless sheath might work better.

Redsnake - the water is pumped from the white tank you see in the photo into two tanks next to it. The water then flows out of these tanks into the drum filter that is sat on a fiberglass stand in the white tank. The drum filter has a small motor that turns the drum when needed.

Do you think putting the probe in some kind of faraday cage would help?

To give you an idea of how far this magnetic field reaches, if I put the probe in one of the other tanks I get the exact same issue. It’s weird.

I do have an AC voltage detector, so that’s something I can try.

This images shows to two other tanks.

> And since salt water are better at transmitting magnetic fields then fresh water that are dimagnetic (repelling magnetic fields) I think that it is possible that this is the source of the disturbances

Fresh water is diamagnetic yes with relative permeability 0.999992. Pretty darned close to 1.0 as we see in a vacuum. Salt moves it closer to 1.0? So max change 0.00008 if I'm understanding correctly. It hardly seems that would be significant. I'm probably not understanding what you're saying. I'm not seeing any scenario where water plays any role in magnetic / inductive interference.

I lean very much towards capactive / electric coupling and away from inductive / magnetic coupling as a cause for this interference.

For capacitive/electric interference, we know there are often high frequency components of the voltage (especially common mode voltage) that can be coupled onto the stator frame and the rotor. Their high frequency means they are easily capacitively coupled. The fiberglass tank and pvc pipes mean they can travel far before being dragged towards ground. Water does indeed cause a big change in electrical permittivity (factor of 80) from air which could explain why removing it from the water makes a big difference.

For inductive/magnetic interference, the motor inductance tends to be a low pass filter so that the high frequency components of voltage do not as much pass into the current, so less high frequency magnetic. Magnetic is also limited by by routing equal/opposite currents together at the source, shielding by motor frame and conduit. And we limit inductive interference by twisting the leads of the target (not much loop area). Also flux flows in loops, I'm not picturing any loop flow out and back through the water that would allow high flux density at the probe. Magnetic permeability barely changes at all between air and water as far as I can tell (unlike electrical permeability which changes by factor of 80). The bottom line I just can't visualize what the water has to do with inductive / magnetic interference. Maybe eddy currents flowing in the salt water, that's the closest thing I can imagine.

We didn't talk about resistive but I lump that in with capacitive. At least they both would presumably involve an ac voltage distibution in the water which is highest at the pump and decreased by introducing ground in the water.

Just my thoughts fwiw, I may be way off base.

ps some guy named electricpete1 made a video on diamagnetic properties of water once https://www.youtube.com/watch?v=2FvWtEdY4sE


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(2B)+(2B)' ?

And yet we don't even know if the water is live.


You guys are offering band-aids to slap onto a potential disaster. Grounding a fiberglass tank? A can around a probe in a liquid conductor? Ground rods?

Keith Cress
kcress - http://www.flaminsystems.com

Itsmoked - What could cause the water to be live?
It’s certainly something I could rule out. When the sump was full and the motor was running I had my hand in the tank multiple times. I’d be very surprised if the water was live. Still something to check

> And yet we don't even know if the water is live.

If water is live with power voltage, then you're suggesting motor shorted to frame and did not trip. Then the motor frame and pump are also live. That's a hazard right off the bat, not related to anything we suggested. And it's a far bigger hazard at the motor than in the tank. But it's unlikely since we protect against this hazard with motor trips and equipment safety grounds on the motor.

> Grounding a fiberglass tank?

I asked what material the tank was in the same post that I suggested grounding the tank. It was only in the response after that we found out it was fiberglass. Ground connection would have no beneficial nor adverse effect on a fiberglass tank.

> A can around a probe in a liquid conductor? Ground rods?

Any equipment safety grounds added between otherwise floating parts and local safety ground bus should only serve to increase personnel safety.

I also suggested to add grounded structure in the tank, which would include some kind of barrier or the can. I don't see the context where your term "ground rods" arises (I never said anything about ground rod). op put steel rods into the sump, which I assume were laid down (not driven) with a cable attached running to safety ground bus. I don't see a big problem with that other than it's ugly and it may corrode or cause other fluid-system related problems. If it didn't fix the problem I hope he took them out.

Any ground connection I mentioned should be connected to safety ground system, not to any neutral.

That's the way I see it. As always I could be mistaken. Feel free to elaborate.

To help check for the dangerous situations you suggest, op could use a voltmeter probing for voltages to ground.

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(2B)+(2B)' ?

Is the pump metal? If so that's a fine connection to the pumped fluid.

I see all sorts of equipment around the tank, any of it could be conducting to the brine.


Pete; Adding a ground rod to a tank of water is a bad idea. If there is a current source you will be doing extensive electrochemistry in the tank and fluid screwing up the chemistry and likely killing any biology the system might be supporting. It is a bandaid. You need to correct the leakage problem at its source not set up a current path that can make the system potentially more dangerous as now you've created a potential voltage gradient.

If there is high frequency energy in the brine then it needs to be excluded from the brine.

Keith Cress
kcress - http://www.flaminsystems.com

> Is the pump metal? If so that's a fine connection to the pumped fluid.

My response was as above: If water is live with power voltage, then you're suggesting motor shorted to frame and did not trip. Then the motor frame and pump are also live. That's a hazard right off the bat, not related to anything we suggested. And it's a far bigger hazard at the motor than in the tank. But it's unlikely since we protect against this hazard with motor trips and equipment safety grounds on the motor.

> Pete; Adding a ground rod to a tank of water is a bad idea. If there is a current source you will be doing extensive electrochemistry in the tank and fluid screwing up the chemistry and likely killing any biology the system might be supporting. It is a bandaid

Yes, it's a very good point you made that it could have all kinds of bad effects (unrelated to electrical safety) depending on what's going on in the tank.... which I don't think we've been told. I didn't think much about that. (fwiw I did suggest above to remove the rods if they didn't help, but it's good you highlighted that). op - what is the process that goes on in this tank?

> You need to correct the leakage problem at its source not set up a current path that can make the system potentially more dangerous as now you've created a potential voltage gradient.

I don't see that adding a grounded component in the tank increases any tank area personal electrical hazard originating from the vfd / motor. Any voltage difference that is created will be less than the original voltage to ground. But let's wait and hear what the process is, there may be a lot of other good reasons not to put anything in there.

=====================================
(2B)+(2B)' ?

In the two tanks next to the white tank we will be adding fish.

I’ll make sure to remove the stainless metal rods that I grounded from the white tank. That didn’t help.

It would be great to discuss this is more detail over the phone but I don’t see anyway to privately contact anyone.

I will add that the pump is properly grounded and protected. I don’t see anyway for it to energize the water without tripping something

How's the shaft grounding on the motor? If it's not great, you're grounding it through the pump and the salt water to the probe.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

Davidbeach - Great question. I have no idea

On that note about shaft grounding, make sure all of your sensors and control circuits are ungrounded and all cable shielding is grounded on one end only or not at all. Stray ground current should not be able to find it's way in to your control and measurement circuits if they're not grounded to start with.

Itsmoke since you only addressed the guys, I guess I am excluded.

My suggestions with the glas jar/bottle are just for troubleshooting purposes, to figur out what is going on.

And as electricpete already stated I think we came to the conclusion early on that if it hade been a short circuit the motor CB or VDF drive would have tripped.

And as tug says and is shown in my post 17 Jul 21 06:18 protentional grounding is important vid VDF drives.

And protentional grounding should not be mixed up protection ground, to different things.
Here the protection ground "PE" cables are always yellow/green not sure what is used in US.
And for potential grounding we use black or transparent so we don't mix them up.
Protection ground is for personal safety and protentional ground for the function of the electronics and the machine.

BR A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

If the bearings on the motor is not isolated to protect them from bearing currents it might end up looking like this.
And if the earth of the pump isn't there it might go through the salt water as suggested.



The solution might be to have a none electrically conductive shaft coupling between the motor and the pump.



Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Red; I didn't have a problem with your crazy bottle gambit, t'was interesting.

I'm very sensitive to water/electricity issues. I've done calls on boats that had problems. In one case a death from someone diving into the water next to a 'bad boat'. In another case someone was paralyzed but their inertia carried them out of the potential gradient, essentially back to life. So when someone talks about problems with electrical equipment associated with water works I get concerned. The very first thing done is to make absolutely sure there's no mains voltage during any part of the process modes in the solution (pump(s) on/off). Brine might as well be liquid metal as far as mains currents are concerned.

The OP's pump in the picture appears to be large and the volute housing appears to be metal. I'm unaware of any VFDs that would be able to detect one phase shorted to the case if the case isn't grounded correctly. Likely it is grounded which would cause an immediate VFD issue no doubt. Hard to tell as the only picture we have is of an unwired pump sitting on makeshift wood.

Did I see mentioned an additional sump pump in the tank too? (Whole nother can of worms if that's true.)

The temp sensor should not be tossed into the tank beyond its dipped part. Temperature excursions will work very hard to draw in brine thru the rinky-dink waterproofing. Rather, the sensor should be in a "life ring" of some sort so only the bottom 3/4ths is in the brine so it will rise and sink keeping the cable/dipped interface forever and always out of the brine. Never should the cable touch the solution. There should be no electrical interaction with that probe because there should be no galvanic connection to it at all.

There should be no high frequency potential in the brine if the VFD was correctly wired to the motor and the grounding rules detailed in the manual were followed. (Something I see ignored 90% of the time.) The high frequency energy between the motor and the VFD wants with-all-its-might to get back to the VFD. Directly back via a large surface area HF conductor.

Keith Cress
kcress - http://www.flaminsystems.com

Thanks again everyone for the feedback and information. As soon as I'm able, I will be testing out and checking as many things you've all listed. I will certainly update as I go.

Quote (Itsmoke)

Likely it is grounded which would cause an immediate VFD issue no doubt. Hard to tell as the only picture we have is of an unwired pump sitting on makeshift wood.

I think that is a old picture from the installation.

Quote (veryconfused)

I will add that the pump is properly grounded and protected. I don’t see anyway for it to energize the water without tripping something

Did I see mentioned an additional sump pump in the tank too?
I think it might have been the drum HEX filter that was turned by a small motor that turns the drum when needed.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Redsanke - There is an additional pump that pulls water from the sump and sends it through a plate heat exchanger, degassing tower and protein skimmer. However, this hasn't been running.

The Hex drum filter has a small motor that is used to turn the drum as needed.

Quote (itsmoked)

I'm very sensitive to water/electricity issues. I've done calls on boats that had problems. In one case a death from someone diving into the water next to a 'bad boat'. In another case someone was paralyzed but their inertia carried them out of the potential gradient, essentially back to life. So when someone talks about problems with electrical equipment associated with water works I get concerned. The very first thing done is to make absolutely sure there's no mains voltage during any part of the process modes in the solution (pump(s) on/off). Brine might as well be liquid metal as far as mains currents are concerned.

I can't argue with huge respect for electrical safety. In my mind if we have this concern then the motor frame and pump casing should be viewed with the same level of concern as the water since the only possible path for line voltage in the water is from stator winding to stator frame to pump casing (line voltage can't get on the rotor)

Maybe some voltage measurements help along the way for checking both for safety and for understanding the problem.
Voltage measurements should have one lead of the meter connected to ground (not any circuit common). itsmoked gave a procedure including using the ground socket on a 3-prong extension cord plugged into a 3 wire outlet (his initial check validates you have a ground connection by checking for 120 volt).
You could check the water to ground as suggested. It would also be interesting to check the motor frame to ground and pump frame to ground and that metal flange a few feet from the pump to ground.
I know it seems like motor casing should be 0 voltage to ground but if the grounding is not effective as Keith mentioned you might still see a voltage from high frequency there.
Data is always good. But of course there is always a caveat. There is always the possibility to see a voltage due to the large loop area involving the test leads and the things they’re connected to and any path that in turn connects those two things.

Quote (RedSnake)

It would be a easy test putting the probe in a glass bottle with freshwater just holding it in the tank to see if it makes any difference.

I see now that test would separate the effects of resistive conducted current (cannot flow through glass) from capacitive current (can flow through the glass). I did a calc (attached) based on the end-to-end resistance and capacitance in a pipe (assuming seawater conductivity 6 mho/m) and I now think the resistive conduction is far more important than the capacitive conduction in the water (by the way the selection of pipe length and diameter and number of pipes are all irrelevant to this particular conclusion since they cancel out in product R*C, but it was still interesting for me to put them in to see the individual R and C values in order to estimate what current might flow). So I suspect your test would cause the indication problem to go away. If the delay associated with temperature measurement in that configuration is considered acceptable (I don’t know, it might not be) it might possibly end up considered a permanent solution to the level indication problem. Would be better than a grounded can with holes.

(EDIT I rechecked my conductivity calc, and it was correct, but the comment "ohm/m" should have been mho/m... if you want to play with that file yourself it is available on smath cloud https://en.smath.com/cloud/worksheet/ZeMETPxF).

To summarize the two potential paths for current to flow:
1 - stator winding capacitively coupled to rotor then conducted through coupling to pump impeller. This path could be solved by shaft grounding (which also improves bearing life) or by insulated coupling.
2 - stator winding capacitively coupled to stator frame then conducted to pump casing. this path might be solved by improving ground connections at the motor.

If we're looking for other quick-check solution I would try grounding that flange a few feet away from the pump, I don't see any harm in that myself.


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(2B)+(2B)' ?

• https://files.engineering.com/getfile.aspx?folder=fb0922e1-57b5-47b7-8a62-7

Heading back a bit from where the discussion is going, try layering RTV sealant on the probe. It won't make it waterproof but it may give you a minute or so of dryness on the thermocouple. Also coat the wires and the entry of the wires into the probe head (that houses the electronics). Do your ON/OFF test with the VFD again (very soon after putting the probe in the water). See if the results look any different.

Electricpete - the flange is pvc not metal.

BrianE22 - I have some RTV sealant, so it’s something I can try

Since I have hade both fresh and saltwater aquariums during many years, it was my big hobby before.
I know that fish can tolerate quit large differences in temperatur as long as they are not rapid.
Of course for growth reasons I suspect that one wants to keep the optimal temperature for that, as konstant as possible.
A glas bottle with fresh water in it would get the same temperatur as the surrounding saltwater and how fast or slow it will even out the temperatur at a change I would guess depends of thickness of the glas.
I think it probable would be acceptable it would at least be possible to adjust the temperatur regulation taking this in to account.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Quote (itsmoked)

I see all sorts of equipment around the tank, any of it could be conducting to the brine.

I’d like to mention that the instrument malfunction was tied to the vfd both by observing it does not occur on other equipment AND that it went away when the vfd was deenergized. Those are two pretty good corroborating clues for purposes of troubleshooting. Add to that the exteremely low probability that a motor shorted to frame without tripping and the risk is pretty darned remote. But does it meet the high level of certainty expected for purposes of electrical safety? No it doesn’t, you're right. Standard safety practice is verify by test that it is deenergized before you put your hand on it if you are thinking about it as potentially-energized equipment.

I don’t in the least mind anyone interjecting safety concerns. If your advice to the op in this particular situation is not to touch the water or any electrical equipment without checking it, that’s fine it's a good idea.

I do feel that my comments in particular were singled out for some reason by you 19 Jul 21 21:20. I don’t see that anything I suggested makes the situation more hazardous other than potential to place the hand in the water which is not something you objected or warned about initially. And your objection seemed to be centered around my comment, citing ground rods and grounded fiberglass tank which I believe you misunderstood.

I'll plead guilty of not thinking through electrical safety before giving my advice. But I'd like to point out that most of the others in this thread did the same. We talked about lifting probe in and out there was no mention of safety. We talked about possible glass, there was no mention of safety. Your own previous comment telling how to measure with an extension cord could have easily been construed by op as a troubleshooting recommendation rather than a safety precaution (that's the way I interpreted it at the time although I can see in retrospect that may not be what you intended). And the water could have been very easily contacted during that process. You did post later talking about lethal but that could've been too late. As for myself I didn't notice your later post using the word lethal in the long string of posts.

So if you're judging this thread for perfect electrical safety, then I screwed up a little. But I'm not the only one (that doesn't mean I screwed up any less but it makes me feel better).

Perhaps a reminder for me to keep electrical safety forefront when giving advice to non-electrical people.

PS - If it's not obvious you touched a nerve with your post 19 Jul 21 21:20. It arouses my defensiveness although you were more concerned about safety than anything else. I felt a need to respond.


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(2B)+(2B)' ?

The suspense is killing me. I need to know what's happening.

I have three additions to confuse this even further.

First, you can't even assume that it's the VFD. There could be other aspects of this process that coincide with the VFD running.

Second, when I have problems with instrumentation, it usually comes back to improper grounding. Make sure everything is grounded PROPERLY.

Third, if there's a question of whether this probe is suitable for use in this submerged brine application can't it get put in a thermowell? Drop it in a copper pipe so it stays dry. You might lose a bit of definition but it's a huge mass of water. The temperature doesn't change quickly.

I'm talking out of my ass so take it all with a grain of salt.

Sea salt then

Quote (sferrari)

First, you can't even assume that it's the VFD. There could be other aspects of this process that coincide with the VFD running

At least to my understanding veryconfused have stated that nothing else has been running while he has conducted his own tests and this is the only VFD in the plant.
So what else could it be?

Quote (sferrari)

Third, if there's a question of whether this probe is suitable for use in this submerged brine application can't it get put in a thermowell? Drop it in a copper pipe so it stays dry. You might lose a bit of definition but it's a huge mass of water.

Not sure a copper pipe would be good for the saltwater fishes.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Veryconfused - the 2 points per second is low sampling rate. Your readout electronics probably has an antialiasing filter that sets up at the proper frequency for the chosen sample rate. You might want to check though. You'd need a very low pass analog filter for 2 pts/sec.

sferrari - I was thinking that too, use a grounded metal thermal well.

My thoughts on thermowell suggestion:

• The existing shielded digital temperature probe (with varying diameters) is an oddball shape to be used in a thermowell. It would have to be a large diameter thermowell. Which part of the probe needs to be in contact with the well I have no idea. Maybe it's ok if you fill it up with thermal compound or water inside. That might be an option to consider for permanent solution if you have something like stainless steel.
• After Keith's comments I was thinking about effect of grounded component in the tank. Assuming we are seeing high frequency capacitively coupled voltage, it would create a small voltage gradient although very low. I assume it wouldn't have any long effect on the fishies, but I don't know for sure.
• I vote let's try the fresh water glass test first.

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(2B)+(2B)' ?

Hi Pete; No worries, I wasn't targeting you. I ran aquariums for nearly 50 years and have seen so many electrical connection to the water over that time it was ridiculous. Almost every "Waterproof" thing wasn't at some point. I'm always leery of water with electrical apparatus associated with it. I was talking instrumentation while thinking safety at the same time.

There is no good reason for the brine to have enough VFD related electrical noise in it to screw up the data logging unless it's galvanically connected to the power somehow. Furthermore the probe shouldn't be caring unless it's also galvanically connected, i.e. wet to it's insides. Otherwise the problem is probably the cable routing OR power filtering OR radiated noise. getting to the cable on the way to the soup or the data logger/controller directly.

Confused: I will repeat that you do not in anyway ground the brine for the sake of the fish. Grounding it is harmless unless something in the future energizes or even small leakage currents get imposed from somewhere. Then the aquaculture will go to hell quickly.

Pay attention to my probe life-ring suggestion above. The cable - insulation goo interface is to be very suspect. It will absolutely fail at some point if not already.

Keith Cress
kcress - http://www.flaminsystems.com

If I do not misremember veryconfused sade they use this probe in all other of there already running tanks without a problem.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Red; I hope you're not inferring that if a couple of earlier probes haven't leaked yet that means a couple of later ones won't?

Keith Cress
kcress - http://www.flaminsystems.com

Briane22 - I don’t think I can change the sampling rate. I will have to read about antialiasing filters.

Itsmoked - I will not ground the brine. I will add that there aren’t any fish in the white tank. And I will try out the probe life ring after I’ve tried the probe in a glass of freshwater.

Redsnake - you are correct, I use these probes in other systems without this issue.

I’m going to install a new probe to completely rule out any issue with the probe.

One tank, one pump motor that need shaft grounding. Nothing moves from location to location because it is location specific. Nothing goes bad when the VFD isn't running because the VFD produces the noise that gets coupled onto the shaft and into the pump. Nothing about a grounded phase, all about induced noise. The most obvious cause of the problem (if it isn't direct contact with salt water) has not yet been addressed.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

Quote (Itsmoke)

Red; I hope you're not inferring that if a couple of earlier probes haven't leaked yet that means a couple of later ones won't?

No I don't.
Changing identical units when one has a problem and another has not, is a common way of troubleshooting complex units or units that can not be checked in another way at least where I work.
If the unit that doesn't "work" starts working and vice vers, I would say with 99,9% certainty it isn't the unit.
If I can not find another fault I would go back and look at 0,1% that was left.
I have been doing this so long, so I know the most unlikely things can happen, sooner or later.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Quote (davidbeach)

Nothing about a grounded phase,

Not sure what you mean here.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

He means he doesn't put any weight on a grounded phase being an issue here.

Keith Cress
kcress - http://www.flaminsystems.com

Quote (itsmoked)

Hi Pete; No worries, I wasn't targeting you. I ran aquariums for nearly 50 years and have seen so many electrical connection to the water over that time it was ridiculous. Almost every "Waterproof" thing wasn't at some point. I'm always leery of water with electrical apparatus associated with it. I was talking instrumentation while thinking safety at the same time.

Thanks. I know you are one of the most laid back and knowledgeable folks here. I overreacted a little. That’s good advice.

Quote (itsmoked)

> There is no good reason for the brine to have enough VFD related electrical noise in it to screw up the data logging unless it's galvanically connected to the power somehow. Furthermore the probe shouldn't be caring unless it's also galvanically connected, i.e. wet to it's insides.

I’m on the same page as you that the probe design (not stated as immersible) and installation (including cable under water) is a huge cause for suspecting a water problem a priori. But I’m also on the same page as redsnake who pointed out: anomaly doesn’t occur in other tanks, anomaly seems to have occurred for multiple probes in this tank, anomaly stops when the vfd stops, anomaly stops when probe lifted. Clearly it's not soley attributable to water intrusion. I think maybe (?) you're suggesting the anomaly is partially attributable to water intrusion but only in combination with vfd noise. Meh, that would require that the water enters enough to disrupt the reading in presence of vfd noise but somehow not enough water inside the probe to cause any problem when vfd is off. I don't 100% rule out water ingress might play a role in that way, but there are way more plausible scenarios to me. Which leads to... I'm on the same page as davidbeach who suggest we focus on High Frequency (HF) voltage coupled into rotor (except I’d go a step further to include HF voltage on stator frame conducted to pump casing, in presence of the possible imperfect stator frame grounding that you had first mentioned... remembering that establishing a good bond to ground can be trickier for HF than for power frequency).

My thinking is that capacitive coupling allows that ac voltage (particularly HF) to jump across the motor airgap without any galvanic connection, and in a similar way it can allow HF to jump across the probe insulation, regardless of whether it is wet or not. That doesn't mean the whole journey is capacitive, the portion of the journey between the pump and the outside of the probe/cable insulation is resistive. The lack of grounded components in the pipe or tank means that any voltage at the pump extends much further through that conducting salt solution before the voltage decays ... so it can more easily get to the probe. Once it gets to the probe, shielding with a ground plane is the best defense against capacitive coupling, but it’s not clear exactly how much/effective shielding we have in this probe and cable. After all that, I think I come to one of the same solutions as you recommended (but for different reasons): We should lift the probe high enough to get that cord out of the water. I would recommend that in general regardless of symptoms, but in regard to solving this particular problem it removes the possibility that interference is transmitted to the underwater portion of the cable through the conductive water. Sure there may also be interference channels that might reach that portion of the cable in air, but those don’t particularly change when we lift the probe out of the water (where the problem went away), and they are harder to fix than simply moving them out of the water (although I wouldn’t mind minimizing the length of exposed cable by extending the conduit as close as possible to the probe... and take the opportunity to ensure there is minimum excess exposed cable length by creating enough conduit length to cover all the cable, or pulling excess cable back inside the conduit if practical, or tucking excess cable back inside if can be done without excessive bending).

That's a lot of general discussion, not much for op unless he wants to understand why we're making some of these recommendations. In terms of practical actions I'd still support voltage check; then either try the glass of fresh water, or else lift probe higher so cable interface is out of water.

I have no doubt things like shaft grounding or alternate probe might possibly end up being the more elegant solution. But we're at the beginning stages, try the above easy few things out first. op does not seem to be in a position to put in place any big changes.

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(2B)+(2B)' ?

I know it's been a while but I thought I would update you all with the solution.

I installed a toroid ring on the output lines on the VFD. This fixed the issue of the noise affecting the temp probe.

Thanks for all your input!

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

Hot dang! Great solution.

Cough up a picture please!

Keith Cress
kcress - http://www.flaminsystems.com

It doesn't look pretty but it works!

It may help some more if you twist the 3 leads together to minimize the loop area between the conductors.

Thanks much for that pic. Nice solution.

Keith Cress
kcress - http://www.flaminsystems.com

Something I didn't think to ask but your picture makes me think I see the problem - Is the VFD to motor cable a proper shielded VFD cable? Are the wires at least in a metal conduit?