Calibrating The Output Impedance of NI Signal Generators
While it is not part of the official calibration procedure, NI provides users the ability to calibrate the output impedance of their Signal Generators.
- Multi meter (DMM) with at least the following specifications:
- DC Accuracy ≤ ±50 ppm
- Resolution ≤ 1 mV
- 50 ohms or 75 ohms feed-through.
Two measurements are required for each configuration to calibrate. One with the feed-through in place, and one without the feed-through. It is the ratio of these measurements that the driver will use to calculate the output impedance of the path. For increased accuracy, the NIFGEN driver provides the user options to calibrate each path, the post amplifier attenuator or the output impedance configuration, separately.
To perform these measurement follow the following steps:
- Measure the impedance of the feed-through that is to be used with the DMM.
- Generate a DC voltage by setting the path and the amplitude level corresponding to the desired post amplifier attenuation to calibrate. A quick reference table can be found below. It is important to note that these are not the only values that can be used but are provided only as a guide.
The 5402/5406 do not allow a DC voltage to be generated on the low gain path, therefore they need to be configured for a square wave and then use a data mask to achieve a DC voltage on the low gain path. The fgen_output_generation_for_cal.vi found in the attached zipped folder fgen_cal.zip demonstrates how to do that.
- Measure the output level with the feed-through in place and document the voltage level. Then, remove the feed-through and take another measurement.
- Once all measurements have been taken use the impedance_calibration.vi to set the calibration constants on the device.
Application Software: LabVIEW Base Development System
Hardware Group: Signal Source (AWG/FG/AO)
Hardware Model: PC-1500PFB, PCI-5401, PCI-5402, PCI-5406, PCI-5411, PCI-5412, PCI-5421, PCI-5422, PCI-5431, PXI-5102, PXI-5104, PXI-5112, PXI-5122, PXI-5401, PXI-5402, PXI-5404, PXI-5406, PXI-5411, PXI-5412, PXI-5421, PXI-5422, PXI-5441
Driver: NI-FGEN 2.6.1
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