level transducer problem

[edbloom]

Sorry for the long winded question but I think it is an interesting one that some may be willing to tackle. SO........

In a series of small vapor degreaser (240V 30A 60Hz) that were just installed at customers facility I am experiencing an intermitant problem with the level detection in one of two tanks.

with a static tank level (any from 0 to 100%) the level (on screen) begins to climb, sometimes but not always to full scale and then returns to normal a short time later.

This happens weather machine is running or in stand by. Some times will work for hours without a problem. However, I have two identical machines powered from the same source that are being effected.

These machines were at our facility for debug for over a month and with continuous running I never saw anything like this problem. My first thought is noise not my math or mechanical. However there is nothing noisy in the machine. 115V pump and 3kw of heat. There are Ultrasonics but this happens with sonics off and unplugged.

Maybe noise on the incoming power but machines are fed from dedicated trnsfmr. I am under the impression that noise unlikely after trnsfmr. Trnsfmrs like to output 60Hz and 60Hz is what you get.

This is a GE fanuc PLC. I am a AB guy so its a little foreign to me. the transducers are 0-25'' 4-20ma Dwyer scaled using a time average. Transducers are wired to IC200ALG342 Card and I am converting the 4-20ma to 0-5v using a 250 ohm resistor.

I would love someone to shed some possible light on what has been causing quite the bit of frustration today. I also would love to make it back home for Christmas.

Thanks.

 

[ndzied1]

First you have to make sure the hardware is working properly.

Put a meter in the 4-20mA loop and see what is happening when the control system thinks the level is climbing. If the loop current is climbing then you can zero in on the transducer.

If the current loop is stable then move on to the 1-5V signal (you shouldn't get to 0V with a 250 Ohm Resistor). Worst case power is only 0.1 W but make sure the resistor is not somewhere in the panel where it is heating up from some other component near it.

If that is OK, I'd look at your "time average" routine. It could be adding in old values or round off errors that are accumulating or just a bad average routine.

Good Luck and let us know what you find.

 

[Gil47]

Is the level transducer an Ultrasonic unit. ?

If so my thought on this is the gasses from the vapor degreaser are upsetting the operation of unit , I have seen this happen in a tank that could accumulate methane gas above the liquid in the tank.

We were able to change a setting that accounted for and corrected the problem.

 

[danw]

You've got a level problem but you didn't tell us what technology the level sensor is. The Dwyer catalog has 18pages of devices that can be used for level sensing.

Which model?

 

[theDave2]

I'll make a W.A.G. I may be wrong, but it'll get you thinking.

The level transducer works by measuring pressure.

When debugging, the tank was vented to atmosphere.

Now the tank is closed up tight and pressure is building up in the airspace above the fluid.

The level returns to normal when some sort of tank vent valve opens or other means happen to put the top space of the tank back to atmosphere pressure or equalize it.

If you actually have a differential pressure transducer, check that the vapor leg is clear and open.

 

[Paul B]

edbloom - Welcome to the forum!!!

 

[shooter]

use a cable from your machine to the control cabinet grounding evrything.
also the transducer to the casing.
check the grounding of the power supply.
just a simple wire from minus to the ground.

 

[rguimond]

Sorry for the long winded question but I think it is an interesting one that some may be willing to tackle. SO........

In a series of small vapor degreaser (240V 30A 60Hz) that were just installed at customers facility I am experiencing an intermitant problem with the level detection in one of two tanks.

with a static tank level (any from 0 to 100%) the level (on screen) begins to climb, sometimes but not always to full scale and then returns to normal a short time later.

This happens weather machine is running or in stand by. Some times will work for hours without a problem. However, I have two identical machines powered from the same source that are being effected.

These machines were at our facility for debug for over a month and with continuous running I never saw anything like this problem. My first thought is noise not my math or mechanical. However there is nothing noisy in the machine. 115V pump and 3kw of heat. There are Ultrasonics but this happens with sonics off and unplugged.

Maybe noise on the incoming power but machines are fed from dedicated trnsfmr. I am under the impression that noise unlikely after trnsfmr. Trnsfmrs like to output 60Hz and 60Hz is what you get.

This is a GE fanuc PLC. I am a AB guy so its a little foreign to me. the transducers are 0-25'' 4-20ma Dwyer scaled using a time average. Transducers are wired to IC200ALG342 Card and I am converting the 4-20ma to 0-5v using a 250 ohm resistor.

I would love someone to shed some possible light on what has been causing quite the bit of frustration today. I also would love to make it back home for Christmas.

Thanks.

Did you try swapping transducers between the two tanks?

 

[theDave2]

Sorry for the long winded question but I think it is an interesting one that some may be willing to tackle.

We're willing. Any any comments back to our replies ?

For the price of a plane ticket, car, lodging and food, plus a nominal fee, I'll be happy to help you solve this in person.