Voltnuts will hate this: Improve your DMM Resolution With One Simple Trick…

Measuring voltages accurately is a basic task for technicians, engineers and scientists. The voltages to be measured range from perhaps few picovolts to several megavolts – a dynamic range of 18 orders of magnitude! But every modern digital multimeter is kinda limited in resolution. The multimeter’s resolution can be stated in the number of digits it can resolve. A 6 digit multimeter can resolve six decimal places going from 0 to 9. In a decimal number system, this corresponds to \(10^6\) numbers or 1 million digitizing steps. Without going much into detail and exposing my limited knowledge on this matter, I’ll just link to Keysight’s Website where everything is well explained.

Older multimeter models such as the shown MeraTronik V543 can resolve only \(2 \cdot 10^4\) numbers in the selected measurement range (e. g. ±1 V = 2 V full scale:  \(2~V/2 \cdot 10^4 \rightarrow 100~µV\) resolution).

MeraTronik Type V543 (PRL T-189), 4.5 digit multimeter with Nixie tube display

One of the best and most accurate digital multimeters in present time – the HP 3458A – has “only” a resolution of 8.5 digits, which hasn’t improved for about 35 years.

HP/Agilent/Keysight 3458A 8.5 digit multimeter

The so-called “Voltnuts” (crazy electro-fanatics) buy those HP multimeters on a second hand market for $3k to $7k. This surely is crazy and overpriced and in my opinion just not worth it. How about buying a couple of cheaper 6.5 digit multimeters (e. g. HP 34401A for about $200 to $400) and combining them in a serial configuration? I’ve achieved a total of 19.5 digit resolution this way*. I was able to display 10 volts up to 18 decimal places, e. g. attovolts resolution and saved a lot of money.

Two HP/Agilent/Keysight 34401A 6.5 digit multimeters in an unusual configuration showing exactly 10 Volts on April 1st…

*If you don’t believe this nonsense, it’s fine. I can live with that. It’s April Fools’ day anyway 😉