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Old 09-14-2000, 07:20 AM
piscis piscis is offline
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Join Date: Aug 2000
Location: San Juan, Puerto Rico 00906
Posts: 121
Analog Input

Could anyone please tell me why I'm getting exactly 20 PSI less shown in the Optimate 620 panel?

I have a 4-20ma pressure transmiter connected to the F2-04AD-1. On two pressure gauges the PSI reads 60 and on the Optimate I'm getting 40 psi. The Scale is 20ma = 100 psi and 4ma = 0 psi

Do you know why this 20 PSI difference?

Thanks evyyone

Puerto Rico
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Old 09-14-2000, 08:52 AM
MacS MacS is offline
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Join Date: Jan 2000
Posts: 143
What is the ladder logic for your scaling formula in the PLC?

The F2-04AD-1 analog input data is a number in the range of 0-4095. To get PSI this raw analog value has to be scaled.

The 20PSI difference is probably in your scaling formula.

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Old 09-14-2000, 09:35 AM
Mike McClanahan Mike McClanahan is offline
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Join Date: Aug 1999
Location: Moore, Oklahoma
Posts: 343
Have you looked in the ladder logic to see what the variable location is reading that you have mapped to the OPTIMATE? The variable should be reading the PSI value.

Conversion is straight forward.

LD (input counts from analog module)
MUL K100 (or K1000 if you want 1 decimal)
DIV K4095
OUT (to the variable location for holding the PSI)

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Old 09-14-2000, 09:43 AM
Tom Jenkins Tom Jenkins is offline
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Join Date: Nov 1999
Location: Milwaukee, WI, USA
Posts: 410
This is how we scale analog data:
         |    |raw data 0-4095
         |    |V2000
         |    |full scale
         |    |V3000
         |    |K4095
              |engineering units
You can get better resolution by adding a decimal place to your full scale value. For example, if you have a 0-100 psig transmitter you can get resolution to 0.1 psig with an implied decimal point by making your full scale value = 1000 instead of 100

I notice that the difference is ecactly = to the 20% offset in the signal. You don't have to do this mathematically in your logic - the input card does it for you. 4 mA = 0 input data, 20 mA = 4095 input data.

[This message has been edited by Tom Jenkins (edited 09-14-2000).]
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