Are 5+ digit DMM's only for low voltage/power? - Page 1
Forum section: electronics / beginners

author: cobbler
author_rank: Unknown
timestamp: January 18, 2016, 04:51:36 am
content: Just wondering if high resolution DMM's are only useful for low power applications? Any other reason the extra digits can be useful for anything other than low power applications?Thx

author: Vgkid
author_rank: Super Contributor
timestamp: January 18, 2016, 04:54:45 am
content: Define low power, voltage(most go to 1kv) current(a few amps). For more you would use a voltage divider(for voltage) or a current shunt(for more current).

author: cobbler
author_rank: Unknown
timestamp: January 18, 2016, 04:58:15 am
content: Quote from: Vgkid on January 18, 2016, 04:54:45 amI guess less than 1v is low power, I have no clue. Guess I am asking when is it useful to really have all the extra digits for real life measuring purposes.

author: Dubbie
author_rank: Unknown
timestamp: January 18, 2016, 11:10:26 am
content: Sometimes the useful signal you are looking at is superimposed on a large voltage. It might change too slow to ac couple.Sent from my phone using Tapatalk

author: AndyC_772
author_rank: Super Contributor
timestamp: January 18, 2016, 11:14:34 am
content: With a high resolution meter you can see small effects, like a battery charging or discharging, or the resistance of a power cable changing as it warms up. You won't be able to measure those with your trusty '830.

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2016, 01:59:59 pm
content: Quote from: AndyC_772 on January 18, 2016, 11:14:34 amFor that application, stability and resolution are far more important than accuracy.I used to work where they sold an impedance meter with a resolution of 0.001dB but an accuracy of 0.1dB. The stability enabled measurements to be taken over the course of a week, which was the time it took to ramp the cable's temperature up and down.

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2016, 02:03:16 pm
content: Quote from: cobbler on January 18, 2016, 04:51:36 amThe limits are defined by the DMM's specification, plus the probe's specification, plus the operating environment.

author: tszaboo
author_rank: Super Contributor
timestamp: January 18, 2016, 02:15:15 pm
content: With a 6.5 digit multimeter, you can build an automatic test setup.It can calibrate or adjust a 80V 2A power supply, which is manufactured by you, to say 0,1% accuracy.With a 3458A for example, you can calibrate a 1000V voltage divider by measuring the two taps.With 6,5 digit, you can null a Wien bridge to one extra digit, compared to 5.5.And a 3458A is excellent to analise the power flow on PCB ground planes. Measuring accurately few microvolt makes all the difference.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 18, 2016, 05:28:11 pm
content: The high resolutoin meters often have a not so high CAT rating. So they are not allowed to work at high power sources like breaker boards. But they still usually have ranges up to 1000 V or similar. It's mor often in the context of lower power where you really needd high resolution / accuracy, but there are a few cases with high volatges too (e.g. supply to a PMT at somthing like 700 V).The other point is that cheap meters often don't have ranges to resolve very low voltages (e.g. µV range). There are a few meters für few digits and low ranges (e.g. 2 mV FS), but not many. From the internal construction the high resolution meters also are usually different: simple meter usually have a switchable divider and than an input for something like 200 mV FS - so they alsways have the divider resistor of typically 10 M. High resulition meters usually have a high impedance (e.g > 1..100 GOhms) input up to about 10-15 V and use a divider only for higher voltages.

author: retrolefty
author_rank: Super Contributor
timestamp: January 18, 2016, 05:42:53 pm
content: Lets be honest, most measurements needed in typical electrical and electronic projects don't require a 5+ DVM. But those of us with 5+ and better DVMs sure treasure them.It's a mild form of volt-nut disease.

author: AndyC_772
author_rank: Super Contributor
timestamp: January 18, 2016, 07:03:07 pm
content: I bought my 34465A for the trend chart capability. The resolution is wasted on me 99.9993% of the time