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Old August 2nd, 2011, 11:58 AM   #1
showshocka
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Wrong analog input readings

Hi. OK, i have a pressure transducer for a run tank level (h20 based) that i just checked for accuracy. it's reading 3.999ma at .001in.of h20, so that's correct for an empty tank. my problem is that the way they have it wired is a signal loop................ A + and - voltage from a dc power supply is going to a PLC 5/8OE analog input card which one wire goes to the transducer to the + terminal, the transducer - terminal goes to the + analog input card on the SLC 5/04. From the SLC 5/04 analog input - terminal goes back to the pressure transducer and is wire nutted to the negative wire that goes back to the PLC 5. analog input card.The biggest question i have is that when the tank is empty the SLC 500 output the the operators panel reads 53LBS and the output from the PLC5 to another operators panel reads 285LBS. i'm thinking it must be the math functions in each of the PLC's. I have a funky little drawing for you guys to laugh at, i'm sure someone will direct me to a program i can use for creating such illustrations.
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Old August 2nd, 2011, 12:09 PM   #2
widelto
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What is the scale from your plc5 to your transducer, and what is your scale from transducer to slc 500. What kind of transducer is that ?? Take a picture of both plcs configs. Take ( voltage/current) measurement at both input/output at the transducer when minimal value is sent from plc5. That will help you with scales.
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Old August 2nd, 2011, 02:05 PM   #3
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If that is a 4-20mA current loop its wired wrong at the SLC500.

From the transmitter + to the PLC5 +.
From the PLC5 - to the SLC500 +.
From the SLC500 - to the transmitter -
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Old August 2nd, 2011, 02:40 PM   #4
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Wired the way it is, I am amazed it works at all.

Perhaps you could post a link to the Data Sheet/Manual for the Transducer.

This might be a good application for a 4-20mA splitter.

Stu....
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Old August 2nd, 2011, 04:30 PM   #5
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And also post the programs for your PLC/SLC. Tell us what modules you are using.
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Old August 2nd, 2011, 04:46 PM   #6
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>A + and - voltage from a dc power supply is going to a PLC 5/8OE analog input card

Where's the loop power supply in the diagram?

Does either PLC provide loop power at its AI terminals? ? ?
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Old August 3rd, 2011, 12:17 PM   #7
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it's a Rosemount 1199 diapram series....the tank is not empty any more but when the tank was empty i got a reading at the transducer of 3.9ma at .001h2o level.
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Old August 3rd, 2011, 12:24 PM   #8
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Quote:
Originally Posted by danw View Post
>A
Where's the loop power supply in the diagram?
sorry about the miss info, but the 24vdc PS is going to a strip terminal where the first connections of the PLC5 is connected to.
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Old August 3rd, 2011, 12:40 PM   #9
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Quote:
Originally Posted by showshocka View Post
it's a Rosemount 1199 diapram series....the tank is not empty any more but when the tank was empty i got a reading at the transducer of 3.9ma at .001h2o level.
Your PLC5 Screen Shot appears to be a Simulation Routine, not live Data.

Stu....
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Old August 3rd, 2011, 12:41 PM   #10
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Quote:
Originally Posted by showshocka View Post
sorry about the miss info, but the 24vdc PS is going to a strip terminal where the first connections of the PLC5 is connected to.
How about an updated Wiring Diagram?

Stu....
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Old August 3rd, 2011, 12:44 PM   #11
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As others have stated, it does not appear that things are wired correctly. Also some of the older PLC 5 analog in cards have dip switch settings to configure an input for either a voltage or current input as well as setting the range. And then there is some configuring that has to be done using a BTW instruction as well. It can be a pain in the !!!

Maybe the problem would be easier to conquer if you cut down in size. First concentrate on getting the transmitter to work with just the slc, then once you get that working, put the plc 5 into the loop.

Go to AB's website and get the info for each analog card. There will be examples on how to wire them for 4-20ma inputs.

Just hang in there, work through it and you will have learned a lot.
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Old August 3rd, 2011, 01:44 PM   #12
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correction, after further in investigation. this is the final wire chase. still the same the operators readouts are off PLC's are still off.
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Old August 3rd, 2011, 01:45 PM   #13
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Quote:
Originally Posted by sthompson View Post
Your PLC5 Screen Shot appears to be a Simulation Routine, not live Data.

Stu....
nope, that was live data as we are running now. why did you think that? the panel-view was showing 4020lbs.
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Last edited by showshocka; August 3rd, 2011 at 01:48 PM.
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Old August 3rd, 2011, 01:49 PM   #14
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Quote:
Originally Posted by sthompson View Post
How about an updated Wiring Diagram?

Stu....
done.
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Old August 3rd, 2011, 01:53 PM   #15
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Quote:
Originally Posted by showshocka View Post
nope, that was live data as we are running now. why did you think that? the panel-view was showing 4020lbs.
Because the Subroutine is called Simulation, and the Add Instruction is preceded by Simulation Timer #9, and you don't usually use an Add Instruction for Scaling an Analog Signal.

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