Saint Germain

I was wondering if anyone has programmed for software adjustments to trim the analog inputs before?

The application is a S7-1214 PLC communicating to a remote Modbus/TCP 4-20mA AI module.

Lets say I have read the AI value from the Modbus moduleinto the PLC and scaled itfrom 4 - 20mA to 0 to 100%. If the AI module is at 4ma, but the PLC value is a little off, let say it is displaying a scaled value of 1.5 instead of 0, how can I program in the PLC to set this valuefrom 1.5 to 0 by pressing a button on the HMI? My first thought is that I would take the difference of the two values and add it totheMIN input on my Scale_X block. Does this sound correct or should the correction factor be applied to the Normalize block input?

Andfor thespan (gain)lets saythat when the Modbus AI module has 20mA at the input the PLC shows a scaled value of 97% instead of 100%. How can I apply a correction factor to this number?
would it be a multiplier?

Any help or comments are appreciated.

This link http://pcoe.nl/@api/deki/files/1791/=18_Instrument_calibration.pdf seems to cover a wide range of calibration related activities.

The span adjustment --- what I've seen in the past is some series of calibration screens to walk the user/operator through the calibration steps specific to a particular application or type of application.

For example, setting the zero and full range (span) of a load cell, pressure sensor, flow sensor, and so on.

The first screen would have some intro and mention what is necessary to successfully complete the calibration or setup and a button to the next screen.

Next screen is often the zero screen.  It might suggest the proper system conditions and then ask for the zero button.  Then when the button is pressed, the input value is saved as the "zero_cal" value.

After the zero is pressed, the zero_cal value is displayed for the user/operator who should have a sense of whether the displayed value is correct.  If so, they can accept and move to the span adjustment screen.  Otherwise, they can change the system and zero again.

On the span screen, the user/operator will do whatever is needed, like adding a weight standard, apply a specific pressure, or other calibrated source to the input signal.  The operator then would select the set range or span option and again get to choose if it was ok or not as the plc would save and display the "span_cal" value.

Once the span value is accepted, the next screen would show the calibration values like zero = xxx.x units, span = xxxx.x units, slope = xx.xx, and possibly allow for a mid-range validation.

If a mid-range validation is needed, then a known operating range source / signal is applied and as long as it falls within acceptable ranges, it is allowed for the operator to accept the calibration as complete.

Otherwise, check the mechanics and wiring, connectors, interface modules for proper operation.  Correct problems and try again.

All that said, your math does not seem to do the slope calculation that would be used to map input counts to user units (0.0-10.0).

Do it by hand and see how it differs from your calculations and you should see the problems quickly enough.