I know its not AB but ...

Arlie

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Jun 2007
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Ellenville,NY
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Hiya folks me again, I have a panasonic FP-e , its a mini plc, I am converting 4-20mA to a T/C port,(0-7mVDC)using a .39ohm resister, all well and good there, have also added the following instruction:

R9010 F313% DT9004, f0.78 , DT1500

R9010 is a normally open contact, sorry can't draw them , now after I get DT1500 how do I convert that to psia ?? what do I multiply by ?? is is 14.87?? any help is appreciated.

yes I know its not allen bradly but my new company uses Panasonic so I have now had to learn to do many things that AB does for you.
thanks again
 
Take the analog value and scale it down to the desired range i.e. if the analog value in the plc is 0-16384 and you need 0-100 then you would mulitply the analog value by approximately .0061 to provide the psi. You get the multiplier by dividing 100 by 16384 (100/16384).

The math does not change with plc's, just instructions etc that are available do. This is simple if your plc has floating point capabilities.
 
Math , me don't mix , I understand the concept, but how do I find out what the value is in the pc?? I need 0-50psia, with the transducer not connected I get a value of 2.69 or close to that, with it plugged in and no press to it at all I get 3569. something, so once I % this by .78 I get 4575.641 so what do I do with that???? sorry as I said me and math just don't mix, need to go back to school I guess
 
Another huge concern I have is that T/C's aren't linear. (I.e., a change of dx on the input will result in a change of dy1 at one place in the range, but a change of dy2 at a different place) That curve changes for different types of T/C's, and all of them do have a portion of their range that is nearly linear.

Loosely translated: It's going to be very hard to get meaningful data putting anything other than a T/C into a T/C port.
 
agreed, however I am asured by the manuf. that it is ok, useing the .39 ohm resister converts 4-20 into tc range of 0-7mVolts. its the math thats got me,
 
Check the manual to see what resolution the input offers. Resolution will be expressed as 8 bit, 12 bit or something similar. To determine the values in the plc take the resolution and multiply by that POWEW i.e. 2^8 (2 to the power of 8 = 256, 2^12 = 4096.

If using Windows it has a calculator in Accesories, with calculator started goto View in Calculator menu on top and select Scientific. The calculator will have more keys on the left, about the middle you will see x^y that is the key you will use. Press 2 then x^y key then the resolution number.

I did not catch that it was going to T/C card, probably be better off if you could get an actual 4-20ma analog card.
 
Arlie said:
agreed, however I am asured by the manuf. that it is ok, useing the .39 ohm resister converts 4-20 into tc range of 0-7mVolts. its the math thats got me,
Click to expand...

Well, how about I explain it this way...

The math is going to be extremely difficult because the conversion at one pressure is going to be different at a different pressure. Yes, you can technically convert the 4-20ma signal into a signal of the right voltage range, but the scaling factors to convert the analog signal to its decimal representation at 2psia will be very different than they will be at 25psia which will be very different than they will be at 40psia.

(Read that to mean that I don't think you can make this work meaningfully over a very broad range of pressures..... That's why T/C inputs are different than "regular" analog inputs)
 
rsdoran said:
Check the manual to see what resolution the input offers. Resolution will be expressed as 8 bit, 12 bit or something similar. To determine the values in the plc take the resolution and multiply by that POWEW i.e. 2^8 (2 to the power of 8 = 256, 2^12 = 4096.

If using Windows it has a calculator in Accesories, with calculator started goto View in Calculator menu on top and select Scientific. The calculator will have more keys on the left, about the middle you will see x^y that is the key you will use. Press 2 then x^y key then the resolution number.

I did not catch that it was going to T/C card, probably be better off if you could get an actual 4-20ma analog card.
Click to expand...
ok so now I can not find the resolution in the manual, this is not a good sign
 
So, after much stress on my part the problem has been solved with simple math, thanks all for you time and support , I have found that I need to slow down and think a little more before jumping off the deep end, had I paid more attention to the process and not taken some things for granted this would not have happened, well live and learn thanks again all.

P.S. not only math but my tech did some miss wiring, solved that and the rest fell into place, never take anyones word for it, check and triple check.
 
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