So why does your lab have a digital bench multimeter?
Why should I have one instead of a new high end multimeter?
The answer is simple, root cause being nearly 30 years ago, at university..
When I started my physics diploma, I made the measurements on superconductors by means of an X-Y chart recorder. I had to convert the voltage of the temperature sensor manually, also the magnetic response signal, and re-draw that by hand in a graph.
I had to make many measurements on many samples, in a small time period, and more and more the resolution of that manual transfer was also not good enough.
Sensor outputs are often non-linear, and the resolution of the sensor signal may degrade, so that even more resolution of the meter is required. Example: temperature measurement with a PT100 at low temperatures down to 14K.
So I started automatic measurements via GPIB bench 5 1/2 DMM, (KEI 193, 194, 199 & scanner, etc.) which at once also solved the resolution / precision problem, which a handheld DMM also would not have covered.
Otherwise, with handheld DMMs only, I couldn't have managed at all these many measurement tasks.
Later, I even needed a 3458A for fast digitization with high resolution, and for calibration of current sources and temperature sensors.
One sentence about the number of nominal digits:
Due to the digitization error, the usable resolution is always one digit less than the specified resolution, i.e. a 4 1/2 digit DMM delivers 3 1/2 digits only.. exactly when you need to measure at 1/10 of its range.
Therefore, a 6 1/2 digit DMM makes absolute sense, when you need some reserve in resolution, or accuracy.
Handheld DMMs are mostly used for qualitative measurements, when you need to know electrical units in the ballpark of a few parts of a % in an electronic circuit.
Even 'high end' handheld (do they really exist? ) are not much better in this sense, and have at least a fundamental stability / accuracy problem, e.g. because they can only have a non-heated voltage reference (i.e lacking LM399). So they can't really be 'high end' in this sense.
Another disadvantage is the lack of 4W Ohm measurements, e.g. PT100 sensors can not be measured accurately.
So in the end, bench DMMs are used for, and are superior over handheld DMMs at:
- automation of data acquisition and conversion via professional / reliable / fast interfaces (GPIB, Ethernet)
- precise, quantitative measurements
- 4W resistance measurements
- high resolution, accuracy, stability especially for non-linear signals
- simultaneous and synchronous recording of different signal sources
Frank