Virtual and DAQmx channels may require field calibration after installation. The available evidence identifies channel scaling and application-side correction as the two current approaches, but it does not establish that separate Offset and Gain properties can be stored in the virtual channel.
Define the Calibration Model
Record the intended equation before changing a scale or channel-return calculation. “Offset and gain” is ambiguous because two common mathematical forms produce different results:
| Convention | Equation | Decision required |
|---|---|---|
| Offset after gain | corrected = gain × raw + offset | Confirm that the offset uses corrected engineering units. |
| Offset before gain | corrected = gain × (raw + offset) | Confirm that the offset uses raw-input units. |
Do not select a convention silently. Use the same equation that produced the calibration coefficients, and document the units of the raw value, corrected value, offset, and gain.
Choose Where to Apply Offset and Gain
Channel scaling can implement behavior similar to offset-and-gain compensation. Alternatively, apply the correction when the application returns the channel value. The evidence does not identify a dedicated Offset or Gain property for virtual or DAQmx channels, so verify the capabilities of the installed configuration and driver before designing around channel-resident properties.
Storing compensation with the virtual channel centralizes calibration data. Application-side correction keeps that data in code or application configuration and therefore requires controls that prevent different consumers from applying different coefficients—or applying the same correction twice.
Update and Verify Calibration
- Capture the existing scale or application-side coefficients before maintenance.
- Determine the required gain, offset, equation order, and units from the calibration result.
- Update the channel scale if it supports the required model; otherwise update the channel-return calculation.
- Read a known input and calculate the expected corrected value with the documented equation.
- Compare the returned value with the expected value, then confirm that no second scale or correction is active.
Keep the calibration values in one controlled location. Record whether they reside in the virtual-channel scale or in the application so later maintenance updates the effective coefficients rather than an unused duplicate.
FAQ
Can offset and gain be stored in a DAQmx virtual channel?
The evidence does not confirm dedicated Offset and Gain properties. Channel scaling can provide similar compensation, so verify whether the required equation can be represented by the configured scale.
Should gain be applied before or after offset?
Use the equation assumed when the calibration coefficients were generated. Confirm whether the model is corrected = gain × raw + offset or corrected = gain × (raw + offset), because the results differ.
How do I verify a virtual-channel calibration update?
Apply a known input, calculate the expected result using the documented gain-and-offset equation, and compare it with the returned channel value. Also confirm that compensation is applied only once.