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Current amplifier enhances NI DMM, DAQ module performance

Posted: 07 Mar 2006 ?? ?Print Version ?Bookmark and Share

Keywords:National Instruments? multimeter? data acquisition device? PXI-4022? current amplifier?

National Instruments further extends its low-level measurement PXI offering for digital multimeters and data acquisition devices with the new NI PXI-4022 guard and current amplifier. This new signal conditioning accessory promises to enhance the resistance, capacitance and current measurement capabilities of the latest NI PXI products, including the PXI-4071 digital multimeter (DMM) and the M Series of data acquisition modules. The high-speed, high-precision amplifier is ideal for in-circuit testers and manufacturing defect analyzers in automated test equipment and consumer electronics applications, added the company.

With the guarding function of the PXI-4022 amplifier, engineers can perform 6-wire resistance measurements for resistors in a network on complex printed circuit board layouts or cable test applications. The 6-wire resistance technique improves the accuracy of the existing 4-wire resistance technique available on most DMMs. The four wires in a DMM provide the source/sense capability to eliminate the effects of lead resistance. The two additional wires in a 6-wire configuration add a unity-gain amplifier to guard the resistor under test against adjacent resistances or contamination across a probe fixture, which would skew the test data. Without this capability, said NI, it is often impossible to make accurate measurements on resistors in complex circuit board layouts.

For low-current measurements, the PXI-4022 module includes high-precision resistors that create a feedback current amplifier to improve measurement accuracy. Often, the sensitivity and resolution of a current-measuring device do not give accurate measurements in the sub-nanoamp range. In addition, these low levels of current are highly affected by physical properties of active devices, such as burden voltages, that can increase current error. Using the module's amplifier and resistor network, engineers can minimize much of this measurement burden voltage, accurately measuring picoamps with femtoamp noise. Also, as a current-to-voltage conversion circuit, this functionality can make it possible for engineers to measure low-level currents (nanoamps) with a multifunction data acquisition device such as an 18-bit NI M Series data acquisition module.




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