Analog Inputs

I am new to PLC programming so forgive my ignorance.

I am having issues understanding the scaling of analog inputs in general.

I am using a Horner PLC.

I have pressure transducer that when air pressure is placed on it it reads a value on the PLC listed below.

20PSI - 6491
40PSI - 6658
60PSI - 6810
80PSI - 6970
100PSI - 7122

If i divide the PSI into the number shown on PLC it is different for each PSI. I would have thought this was linear.

Please help me to understand how this works and what I am doing wrong.

Thanks

Tim Duell
Buckeye Shapeform

The function is near linear

PSI = (Reading - 6333.25) / 7.8875

[Edit: Excel gives PSI = (Reading - 6338) / 7.87]

Your transducer must have a supressed zero. Either that or there's something wrong with your wiring.
Can you give us the make & model
The input range of your PLC card

there is a piece wise function instruction in AB PLC,but i don't know is there in Horner PLC

For Horner PLC (XLT) I use the "scaling element".

Input is the value for your AI e.g. 0 - 2^15 ( 0-20mA) and for the output 0 - 100 for a output scaled in percentage.

Fonzie66 said:

For Horner PLC (XLT) I use the "scaling element".

Input is the value for your AI e.g. 0 - 2^15 ( 0-20mA) and for the output 0 - 100 for a output scaled in percentage.

Click to expand...

I second the above.
You don't have to do your own math/scaling. Use the "Scale" function of the Horner, plug in your engineering units and define the Scale values (0-100) or whatever that may be.
Look in the manual for your unit (pressure transducer & Horner unit) and you''l find the engineering values to work with.
(0 PSI may be 0 and 100 PSI may be 32767 or so, so read the manual first).

Depending on the Horner model and the type of I/O used, 0-32000 is probably the input range to use.

Assuming that the analog is onboard I/O, you should also check your configuration settings--make sure that it is set for 4-20 mA (or 0-10 VDC) in both the I/O configuration/module setup and the internal jumper settings. If there is a mismatch, you can get an offset 'zero' value.