Maximum voltage ratings in bench multimeters - Page 1
Forum section: electronics / testgear

author: NaxFM
author_rank: Regular Contributor
timestamp: October 12, 2022, 06:06:05 pm
content: I was doing a little research about the maximum voltage rating and found very little info on one particular aspect.I was interested in the maximum voltage between Input Lo and Sense Lo, but only the manuals of the keysight dmms provide this info (200Vpk), and only for the truevolt series. For the 3458A i couldn't find nothing, same for the keithley dmms.Do you have any info regarding this limit?I was also wondering if a voltage present between the Sense lo and Input lo terminals could throw off the measurement on the input side, but i doubt this may be the case.Edit: for example the manual for rigol dmms regarding 4 wire resistance measurement states:LO Sense/200 mA-LO protection limits: 0.5 Vpk. The current input fuseon the rear panel provides the current passing through LO Sense/200mA up to 500 mA protection.But it seems a very weird explaination, because if the protection would kick in at only 0.5V this would severly limit the capabilities of the DC ratio function.Edit 2: so, apparently the rigol shares the sense lo terminal with the 200mA current input and doesn't have DC ratio function, so a limit this low makes sense now.From siglent manual:HI Sense-LO Sense protection limitation: 200Vpk.LO Sense-LO protection limitation: 200Vpk.It seems the siglent also has 200Vpk between LO input and LO sense, tho in the second line they forgot to write "LO input"and wrote just "LO"

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2022, 06:24:04 pm
content: Many/most designs with 4W resistance have fairly low impedance between the two LO terminals, so you can't have any significant voltage there, nor would you during any proper use of the instrument. Fluke bench DMMs have this marked as a maximum of 1 volt. I'm not seeing anything that indicates you can have 200 volts between the two LO inputs on any Keysight meter, TrueVolt or not. Can you post what you are looking at?

author: NaxFM
author_rank: Regular Contributor
timestamp: October 12, 2022, 06:29:04 pm
content: Quote from: bdunham7 on October 12, 2022, 06:24:04 pmIn the manuals it states"The HI and LO sense terminals are used for DCV ratio measurements and four-wire resistance and tem-perature measurements. The Measurement Limit is 200 Vpk for all of the terminal pairings: LO sense to LOinput, HI sense to LO input, and HI sense to LO sense."It's on page 18https://www.allaboutcircuits.com/test-measurement/multimeters/34465a-digital-multimeter/manual/

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2022, 07:04:54 pm
content: Read the note just below that for a clue as to what is going on. In this particular case it appears that they do have high impedance between those two terminals in the DC ratio mode. Many other meters don't use that set of terminal for DC ratio, or if they do they cannot do DC ratio unless the two voltages have a common LO.From the 34401A manual regarding DC ratio:The Input LO and Sense LO terminals must have a common reference and cannot have a voltage difference greater than 2 volts.Edit: I read the DC Ratio section of the manual (p.60 of your linked manual) and I wonder if there is some confusion somewhere. I'm not quite clear as to how this works after reading it.

author: J-R
author_rank: Super Contributor
timestamp: October 12, 2022, 07:06:01 pm
content: I have a Keithley 2010 and the limit is 350V peak.It requires the LO terminals to be common.

author: manupthehills
author_rank: Contributor
timestamp: October 12, 2022, 09:57:40 pm
content: For the 3458A those limits are mentioned on page 26 of the Calibration ManualM.