Multi-channel High-voltage Impedance Analyzer
This system was developed to measure the impedance frequency response or complex impedance at a given frequency of up-to 16 loads with a common ground simultaneously. The system includes four programmable measurement ranges, optimised for the given application which required the measurement of capacitances from 2nF to 20nF, resonance impedances from 300Ω to 4kΩ, and excitation voltages of up to 100V.
The impedance analyser is calibrated against custom-built test impedances and achieves a tolerance of better than 1% for all measurement ranges within a measurement time of less than 1 second.
This system comprises of a custom 16-channel high-voltage impedance analyser (HVIAx16), a four-channel high-voltage linear amplifier (PD200x4) and a National Instruments multifunction I/O Device (NI USB-6349). The National Instruments data acquisition device is used to generate and record test signals, and to relay digital signals between the PC and instrument. All signal processing functions are performed on the PC and the system is controlled by Python commands on the host PC. The power amplifier is used to generate the required high voltages and currents and the impedance analyser measures the voltage and charge across the devices under test.
As illustrated on the right, the impedance of a single channel is analysed by applying a voltage to the device under test through a series reference impedance. The reference impedance is selected so that the maximum expected current results in less than +/-10V voltage drop. The implemented method is a high-side current measurement which is required by the application. Since this approach leads to a voltage drop across the reference impedance, the load voltage and current must be measured. If more than 10V is dropped across the reference impedance, the chosen measurement range must be increased.
The analog instrumentation provides two measurements per channel to the digital signal processing system which converts the two measurements to impedance. For the capacitive measurement, the capacitance and angle are calculated from the complex impedance. For the frequency response measurement, the magnitude and phase of the complex impedance are calculated.
