OPEN/SHORT Compensation

OPEN/SHORT Compensation

In most practical applications, the DMM is connected to the DUT with switches and/or fixtures. These switches and fixtures can introduce undesired errors into the measurement. Compensation minimizes the errors between the NI 4072 and the DUT.

Offset Compensation

Compensation consists of measuring the error and applying the measured error to the actual measurement to correct and minimize the errors introduced by the test system. The compensation functions must be set before taking any measurement at a specified function and range.

Any change in range or function defaults the compensation type to none. Therefore, you must calculate these values again. To provide maximum flexibility in the test system, the compensation values are returned by the API. You can manipulate, store, and load these values for high channel-count systems.

To perform OPEN compensation for capacitance and inductance measurements, complete the following steps:

1. Disconnect the DUT from the DMM at the DUT.
2. Configure the DMM for capacitance or inductance at the desired range.
3. Call niDMM Configure Cable Comp Type or niDMM_ConfigureCableCompType, and set the Cable Comp Type to CABLE COMP OPEN.
4. Set up an open condition, where nothing is connected to the test fixture. If the switching system in use has similar capacitance on different channels, you can dedicate one channel for open measurements. Cables and switches with low capacitance and low-path resistance are recommended.
5. In LabVIEW, call niDMM Perform Open Cable Comp or niDMM_PerformOpenCableComp while the input to the DMM is open. This VI or function returns two values: conductance and susceptance.
6. Pass the two values from the previous step into niDMM Configure Open Cable Comp Values or niDMM_ConfigureOpenCableCompValues. Passing these values subtracts the open measurement from all subsequent measurements.
7. Perform the desired measurement.

To perform SHORT compensation for capacitance and inductance measurements, complete the following steps:

1. Disconnect the DUT from the DMM at the DUT.
2. Configure the DMM for capacitance or inductance at the desired range.
3. Call niDMM Configure Cable Comp Type or niDMM_ConfigureCableCompType, and set the Cable Comp Type to CABLE COMP SHORT.
4. Set up a short condition at the end of the test fixture, using a low-impedance connection between the HI and LO terminals. If the switching system in use has similar inductance on different channels, you can dedicate one channel for short measurements. Cables and switches with low capacitance and low path resistance are recommended.
5. In LabVIEW, call niDMM Perform Short Cable Comp or niDMM_PerformShortCableComp while the input to the DMM is shorted. This VI or function returns two values: resistance and reactance.
6. Pass the two values from the previous step into niDMM Configure Short Cable Comp Values or niDMM_ConfigureShortCableCompValues. Passing these values subtracts the short measurement from all subsequent measurements.
7. Perform the desired measurement.

OPEN/SHORT Compensation

To perform OPEN and SHORT compensation for capacitance and inductance measurements, complete the following steps:

1. Disconnect the DUT from the DMM at the DUT.
2. Configure the DMM for capacitance or inductance at the desired range.
3. Call niDMM Configure Cable Comp Type or niDMM_ConfigureCableCompType, and set the Cable Comp Type to CABLE COMP OPEN AND SHORT.
4. Set up an open condition, where nothing is connected to the test fixture. If the switching system in use has similar inductance on different channels, you can dedicate one channel for open measurements. Cables and switches with low capacitance and low path resistance are recommended.
5. Call niDMM Perform Open Cable Comp or niDMM_PerformOpenCableComp while the input to the DMM is shorted. This VI or function returns two values: conductance and susceptance.
6. Pass the two values from the previous step into niDMM Configure Open Cable Comp Values or niDMM_ConfigureOpenCableCompValues.
7. Set up a short condition at the end of the test fixture, using a low-impedance connection between the HI and LO terminals. If the switching system in use has similar inductance on different channels, you can dedicate one channel for short measurements. Cables and switches with low capacitance and low path resistance are recommended.
8. Call niDMM Perform Short Cable Comp or niDMM_PerformShortCableComp while the input to the DMM is shorted. This VI or function returns two values: resistance and reactance.
9. Pass the two values from the previous step into niDMM Configure Short Cable Comp Values or niDMM_ConfigureShortCableCompValues.
10. NI-DMM takes the four values measured on open and short conditions to compensate all subsequent measurements.
11. Perform the desired measurement.

Note  Due to ambient temperature variations and other environment changes, such as humidity, it may be necessary to perform OPEN and SHORT compensation at least once a day. When using a switching system, verify that the OPEN and SHORT measurements on the reference channel closely match the measurements on the rest of the channels being compensated. If this compensation method does not meet your error budget requirements, OPEN and/or SHORT compensation must be performed on the same channel used to take the DUT measurements.