Introduction

Many years ago I’ve had a chance to play with Advantest 6581T which is a special version of the 6581 8½digit DMM. It was donated to xDevs for experiments by a friendly lab and later I’ve donated it to spencer member of our chatbox for his experiments. These DMMs have some firmware and hardware issues that prevent them to demonstrate better metrological performance more fitting of 8½-digit DMM. These issues can be resolved with extensive workarounds and reworks which are documented elsewhere. 6581T’s got rather popular among metrology enthusiasts due to much lower cost relative to traditional long-scale meters like HP 3458A or Keithley 2002.

Later multimeter business of Advantest separated into separate organization – ADCMT. Japanese ADCMT still active in instrumentation business and have line of multimeters from 5½-digit Model 7355 to high-end 8½-digit Model 7481/7482. But far less known Model 7480 was designed for exclusive Advantest internal semiconductor test systems. Model 7480 does not have current, AC voltage/current functions and only provides DC voltage and resistance measurement capability. There are no public manuals or documentation available from ADCMT or Advantest for 7480.

Our friend Steve ‘VE7FM’ at https://fmlabs.ca/ acquired ADCMT 7480T for some testing and experiments and published internal teardown on his site.

Internal design of ADCMT 7480T looks like cost-optimized version of older 6581T but still have some interesting components like LTZ1000 reference and ACAL functionality. Recently I’ve got a chance to run some Python test scripts on pair of 7480Ts against known good tandem of 3458A meters with high-end Fluke 5720A source.

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INL performance test results

This test was performed remotely over the internet connection to friendly laboratory. Two ADCMT 7480T were made available to test their performance. For this I’ve enlisted my friend Alex to connect DUT meters together with trusty HP 3458A to nice Fluke 5720A calibrator as a signal source. Both HP3458A were used as linearity calibration reference as they were tested extensively before. Python scripts were used to collect data points and perform analysis on resulted random data points within every range. Overall block diagram for connections shown below.

Scripts used to test are below:

Data collection script for all DVMs and 5720A

Linearity plotting script using matplotlib and scipy

Configuration file for plotting script

Running sequence of measurements was done over a weekend during ~30 hours period with 6144 samples at 1024 random points captured for each DC Voltage range for good coverage.

And finally results of the sweeps:

INL sweep with random points on 100 mV range

Low DC Voltage range shows lot of spread and noise around, compared to reference 3458A meters.

INL sweep with random points on 1 V range

INL sweep with random points on 10 V range with 2.19999 V range of 5720A.

INL sweep with random points on 10 V range.

INL sweep with random points on 100 V range.

Overall results show that 7480T is not a match to traditional 8½-digit DMMs which typically show INL performance better than 0.2 µV/V.

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