Analog Problem

[Fred Floggle]

Having just had a glance at the manual I don't think it matters how you do the scaling - does this thing go full scale 4096 or more - if only 4096 , I would definitely try and turn the function off - it is more trouble than it is worth .You did mention that the card didn't support full scale on wire break - I think if you test it that FSD will be more than 4096 - the maths could never give those results .

 

[robert mooli]

Hi
We have got several problems of the like but i think the most basic way is to find out whether the card is faulty,pgm, or the transducer by simulating their inputs ie have current injector(4 _20ma range )conect it to the card as if it was 4_20ma from the transducer,visualise any changes as you vary 4_20 input range from the meter,swap the meter leads,Do the same for the transducer just connect pressure source to the trans. measure ma out put. hope thes helps

 

[jimbo3123]

OK question, I have a pressure transducer for pressure range of 0 200 PSI. Puts out a 4 - 20 MA signal. I installed this yesterday and the lines are empty so there is 0 psi, but my PLC is saying there is 200 PSI. I took my fluke measures the MA signal it shows .004 MA.

Is that .004 mA or .004 A (4 mA)? I seriously doubt it's .004 Mega Amps (or 4000 Amps) as you abbreviated.

 

[BoxerBrats]

it was .004 milliamps

 

[kamenges]

Originally posted by BoxerBrats:
it was .004 milliamps

I think you mean 4mA or 0.004A.
0.004mA (0.000004A) is an infinitesimally small current flow for anything you encounter in the machininery world.

Keith

 

[BoxerBrats]

I was using a FLUKE model 78 set on mA setting read .004

 

[rsdoran]

I am curious, did you find the problem? That low of a reading I would pretty much ignore, technically as was stated any reading below 4ma will/should give a 0 reading, and .004 is pretty much 0.

You stated you tested it prior to installation, did you do an analog test and calibrate thru the scale?...ie did you verify what 4ma or less would show? what 4.5 shows? 5.3? 7.8? 13.4? 20.0?

Was there anything different when installed then when you tested?..ie same devices? same wiring? same power supply? Was the transducer dropped?

Did you test the transducer once installed to verify an output?

At this point I dont have enough information to actually provide an answer. I am not sure what has been done and what hasnt.

 

[leitmotif]

At this stage I think everyone is getting confused. Here is what I would do:
1. Install a pressure gage for desired range of 0 to 200 (psi I think it was).
2. IF you have to remove transmitter and jury rig into a source of pressure (plant air for example). Install pressure gage.
3. Connect Fluke VOM in series to read milli amps.
4. Turn on PLC and be able to read what the input bit values are.
5. THEN
at 0 psig record pressure, mAmps, and input bit values
repeat for 50 and 100 and if you can get there 150. Another set for 200 psi would be nice but you should be OK with the above scenario

Let us know what these values are.
THEN we will (most important YOU) will know what is going on.

If a liquid you may want to consider static head, but that can come later you need to do a calibration and "does this thing really respond correctly??""

Dan Bentler

 

[robert mooli]

I agree with dan this will work

 

[Unregistered]

Check your transducer. They can get damage during installation easily.
Lightly press the pressure head with your palm. This will simulate a few lbs and thus ma into your AI.
Many transducers are 2-wire transmitter so check your 24VDC ps and polarity as well.

 

[BoxerBrats]

I am curious, did you find the problem? That low of a reading I would pretty much ignore, technically as was stated any reading below 4ma will/should give a 0 reading, and .004 is pretty much 0.

You stated you tested it prior to installation, did you do an analog test and calibrate thru the scale?...ie did you verify what 4ma or less would show? what 4.5 shows? 5.3? 7.8? 13.4? 20.0?

Was there anything different when installed then when you tested?..ie same devices? same wiring? same power supply? Was the transducer dropped?

Did you test the transducer once installed to verify an output?

At this point I dont have enough information to actually provide an answer. I am not sure what has been done and what hasnt.

I did this at the shop, then installed at location. It is located out of town, but will be going back later this week. I 99% positive that I do have positive, and negative backwards going out to transducer.

 

[automan]

You had connected the PT with wrong polarity?

Every thing is clear.
you had connected wrong polarity and your analog input reads -4mA instead of 4mA.
Your measurement confirms that everything is ok but polarity.you read 4mA( and not .004mA )

 

[Tom Jenkins]

Every thing is clear.
you had connected wrong polarity and your analog input reads -4mA instead of 4mA.
Your measurement confirms that everything is ok but polarity.you read 4mA( and not .004mA )

Probably not. If a loop powered (two-wire) transmitter is hooked up with the wrong polarity it almost always provides no signal, not a reversed signal. The 0.004 mA is probably the actual reading, and is just zero drift on his meter. For all practical purposes this means a zero signal, and the most probable cause is reversed polarity in his wiring.

 

[Pego]

The Fluke 78 does not have a mA range..
If the 0.004 mA is indeed meassured(with another meter than the Fluke 78) it is probably a leakage current due to wrong polarity of the transmitter.

 

[rsdoran]

No the 78 doesnt have a ma setting but the AMP setting is good for 4ma-10a DC resolution .001 and 40ma-10a AC resolution of .01.
http://us.fluke.com/usen/products/specifications.htm?cs_id=2279(FlukeProducts)&category=AUTO(FlukeProducts)

I wouldnt use that meter in industrial work, I prefer the 87 now the Series V 87.
http://us.fluke.com/usen/products/Fluke80SeriesV.htm?catalog_name=FlukeUnitedStates