Calibrating I/O Modules

Calibration ensures that input and output (I/O) modules provide accurate and reliable measurements. It involves comparing the output of a measuring device with a reference standard of known accuracy and adjusting the I/O if any discrepancy is found. Calibration corrects any input channel discrepancies that may result from sensor drift, wiring issues, installation changes, or other factors differing from the factory baseline. Each calibration event is recorded with a date for full 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 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. See Role Permissions for details.
Note - Changing any Analog Input (AI) configuration parameters such as Input Type, Linearization Type, Cluster/Slot, PV Offset, PV Range High/Low, Input Range High/Low, Shunt Value, or CJC Type may invalidate an existing user calibration. After making such changes, review and repeat the user calibration if necessary.
Note - User calibration resets automatically when the module serial number, channel number, or User Calibration Point Count is changed, see 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.

Calibrating I/O modules is essential for several reasons:

  • Accuracy - Ensures precise readings essential for industrial processes, scientific experiments, and quality control.

  • Compliance - Supports meeting statutory and industry standards, helping avoid penalties or product recalls.

  • Safety - Ensures devices operate within specified accuracy ranges, reducing operational risk.

  • Quality Control - Maintains device reliability and consistency.

  • Maintenance - Helps identify potential issues early, avoiding costly failures.

Pre-requisites

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

  • A precision electrical signal source capable of applying a defined signal into 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 Data 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 target points (2 - 6) is defined by the User Calibration Point Count for the channel, see 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. This is the process value that corresponds to the signal that will be applied to the input during the next step:

  7. At the corresponding sensor location, apply a measurement that matches 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 and matches the Target PV as closely as the reference allows. When the Actual PV is stable at the Target PV, 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.
See also, Configuring an Analog Input Channel.