Calibrating I/O Modules

Calibration ensures that input and output (I/O) modules provide accurate and reliable measurements. It involves comparing an I/O value with a reference standard of known accuracy, and where necessary, applying a correction to minimize any discrepancy. Calibration can correct or compensate discrepancies introduced by the system, including sensor characteristics, wiring, installation changes, or other factors that differ from the factory calibration conditions. Each calibration event is recorded with a date to provide traceability.

Note - Only available for analog input modules/channels.
Note - You can only access this screen if you have the Can access I/O Channels permission. To calibrate I/O modules you must also have the Can calibrate I/O permission. If you require access to these functions but do not currently have the necessary permissions, please contact your system administrator.
Note - User calibration resets automatically when the channel number, or User Calibration Point Count is changed, see the User Calibration Point Count option in the Configuring an Analog Input Channel for details. In these cases, the channel reverts to factory calibration and a new user calibration is required.

 

CAUTION

RECALIBRATION REQUIRED

Review the user calibration and repeat it if necessary after changing any Analog Input (AI) configuration parameters.

Failure to follow this instruction can result in incorrect Analog Input readings
Note - Changing any of the following Analog Input (AI) configuration parameters can invalidate the existing user calibration: Input Type, Linearization Type, PV Offset, PV Range High/Low, Input Range High/Low, Shunt Value and CJC Type.

Calibrating I/O modules is essential for several reasons:

  • Accuracy - Ensures that input and output values remain within specified accuracy limits, supporting reliable process measurement and control.

  • Compliance - Demonstrates compliance with statutory and applicable industry standards, providing help in avoiding penalties or product recalls.

  • Safety - Ensures that measurements used for monitoring and control remain within specified accuracy limits, reducing operational risk and incorrect process decisions.

  • Quality Control - Supports reliability and consistency of measurements, helping maintain process and product quality.

  • Maintenance - Identifies potential issues early, such as measurement drift or other performance changes before they significantly affect the process, avoiding costly failures.

Pre-requisites

  • Controlled, calibrated reference equipment such as a calibrated furnace or bath for calibrating a complete temperature loop, or

  • A precision electrical signal source capable of applying a defined signal to the input through the sensor wiring.

Tip - You can calibrate as soon as the module is present; however, it is recommended that you set the correct input type and range first so that the reference signals match the channel’s intended use.

To calibrate an I/O module:

  1. From the EPM User Interface screen, select Options - Device I/O - Hardwired I/O:

  2. The Hardwired I/O screen displays, select an appropriate analog input module:

  3. Select the required channel from the Channels tab. The Input calibration screen displays on the right-hand side:

  4. From Input calibration, select Expand to display the calibration options, then select Start to begin the calibration:

    Note - By default, all analog input modules are factory calibrated.
    Note - The Input Calibration header displays the last successful calibration (factory or user calibration) and the date.

  5. The Start user calibration screen displays, select Continue:

    Tip - The Operator Panel displays 'Calibrating' as the status.
    Tip - Select Discard at any time to stop calibration and restore the previous calibration state (factory or user calibration).

  6. The calibration indicator highlights each calibration point in sequence. The number of calibration target points (2 - 6) is defined by the User Calibration Point Count configured for the channel, see the User Calibration Point Count option in the Configuring an Analog Input Channel for details.

    For each highlighted calibration point, enter the Target PV in engineering units. The target PV is the process value that corresponds to the signal applied to the input in the next step:

  7. At the corresponding sensor location, apply a known reference signal measurement that corresponds to the Target PV. This can be performed by either :

    • Using controlled calibrated equipment, for example, a calibrated furnace or bath for temperature loops, or

    • Injecting a precision electrical signal directly into the sensor wiring.

  8. Wait until the Actual PV on the calibration panel stabilizes as close as possible to the Target PV within the accuracy of the reference equipment. When the Actual PV is stable, select Confirm to save the new calibration point:

    Tip - Select Fast settle to temporarily disable or bypass input filters for faster stabilization.

  9. Repeat Step 5 to Step 7 until all calibration points are completed. The target indicator turns green:

  10. After successful calibration, the channel is marked as 'User Calibrated' along with the calibration date:

    Use the Reset calibration option if required to delete all stored user calibration data (old/new) for the channel/module and restore it to its original factory calibration values.

    Note - The Reset calibration option is only available when a channel is in a user calibrated state and no calibration is currently in progress.
Related topics - Configuring an Analog Input Channel.

Last update - September 2026