Bench DMM with simultaneous DC+AC RMS - Page 1
Forum section: electronics / testgear

author: forrestc
author_rank: Unknown
timestamp: April 08, 2014, 12:16:24 am
content: I am looking for a DMM which can measure and display both DC voltage (average) and AC voltage (mV ripple) at the same time.I have a handheld unit that does this but I really would like to get more of a bench style instrument. I recently bought a DM3058E based on the premise that this unit does this - but in reality it switches between the DC and AC measurement modes, causing the internal relays to cycle with each measurement. Because this is going to be a common measurement for me I'd rather find something which isn't going to wear out internal relays when in this mode.I don't need a lot of accuracy/resolution. A plus would be support of ACV+Frequency and so on. And no, I don't want to just use my scope....Any ideas?

author: dr.diesel
author_rank: Super Contributor
timestamp: April 08, 2014, 12:29:07 am
content: What is your budget?I recently bought a Hameg HMC8012 which does two measurement simultaneously. It's kinda pricey for a 5.5 digit meter but it's somewhat unique, and I like odd ball stuff.

author: forrestc
author_rank: Unknown
timestamp: April 08, 2014, 12:56:21 am
content: Quote from: dr.diesel on April 08, 2014, 12:29:07 amLet's just say I don't want to spend more than I need to, but I'm not opposed to spend a few/several hundred dollars on this if necessary. I'm a big fan of finding the right tool for the job, but don't feel the need to pay large for something I'll never use.Quote from: dr.diesel on April 08, 2014, 12:29:07 amLooking at a video online about the HMC8012 right now. Looks nice so far. I also don't hear relay clicking. Mine behaves in DC with a secondary AC display mode like the agilent shown atdoes around 27:35. Have you had yours in dual display mode and does it start clicking?

author: dr.diesel
author_rank: Super Contributor
timestamp: April 08, 2014, 01:00:48 am
content: I have a video of it on YT, in dual measure, plus more here on EEVblog. (I'm mobile right now so no link!)

author: forrestc
author_rank: Unknown
timestamp: April 08, 2014, 01:10:54 am
content: Quote from: dr.diesel on April 08, 2014, 01:00:48 amI found the dual measure function video of yours, or at least I think it's yours (same truck picture on the account).Yes, this seems to be just the ticket. There is a longer review by someone else and a lot of the stats functions (and wattage measurements) that it will do looks like it might have applications I wouldn't have even considered a DMM for...-forrest

author: dr.diesel
author_rank: Super Contributor
timestamp: April 08, 2014, 01:18:26 am
content: Yeah, its a great meter and offers a true dual measure without switching modes.If you get really interested I can put up further videos.

author: Rycroft
author_rank: Contributor
timestamp: April 08, 2014, 01:28:30 am
content: The Agilent 3402A will do it, I believe.

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2014, 01:45:06 am
content: Not in the price range but the 8845A and 8846A have dual readouts.

author: forrestc
author_rank: Unknown
timestamp: April 08, 2014, 02:58:24 am
content: Quote from: Rycroft on April 08, 2014, 01:28:30 amIt does have dual displays but if you look atat around 27:30 you'll see the type of implementation I'm trying to avoid. The U3402A seems to do exactly the same thing as my Rigol - it takes one reading, switches the relays around internally, and then takes the other one.The keithley 2110 also seems to do this ... seearound 2:45.I realize that ACmV and DCV may not require a relay switch to read both, but without buying them I can't tell as the manual isn't going to tell you.Contrast/Compare the HMC8012 mentioned earlier...

author: forrestc
author_rank: Unknown
timestamp: April 08, 2014, 03:10:56 am
content: Quote from: robrenz on April 08, 2014, 01:45:06 amThey're close enough that I'd consider them. The only video I could find which showed dual readouts didn't have good enough audio for me to tell for sure if it was doing the "switch relays between each reading" thing or not. Didn't sound or look like it was, so this might be a possibility.Do you by chance have access to one?

author: mimmus78
author_rank: Unknown
timestamp: April 08, 2014, 09:04:05 am
content: Also Keithley 2001 has dual readout (trial if you count also frequency) ... but it switches relay between each reading.

author: dr.diesel
author_rank: Super Contributor
timestamp: April 08, 2014, 09:11:40 am
content: Quote from: forrestc on April 08, 2014, 03:10:56 amThe 8846A is a fantastic high quality 6-1/2 digit meter, probablythe6-1/2 digit meter to have. However I didn't think it could do true dual measure, but robrenz has one and I'm sure he can tell you/verify. I have it's younger brother and it cannot do true dual.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: April 08, 2014, 10:58:37 am
content: It's not a Bench meter but the Brymen BM869 can. (if I remember correctly, I will check it later)edit:Dual screen: AC+DC RMS and AC (x.xxx)Dual screen: DC and AC

author: linux-works
author_rank: Super Contributor
timestamp: April 08, 2014, 11:15:37 am
content: fluke 45 has dual display.

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2014, 11:55:47 am
content: Quote from: forrestc on April 08, 2014, 03:10:56 amI am very fortunate to have one.No relay switching, the dual display is continuous and the same update rate as single display.primary secondaryDCV ACVACV DCVACV HzDCI ACIDCI DCV (three wire hookup)ACI DCIACI HzHz PeriodPeriod HzTemp Ohms

author: KedasProbe
author_rank: Frequent Contributor
timestamp: April 08, 2014, 12:28:30 pm
content: Quote from: robrenz on April 08, 2014, 11:55:47 amACA = A Current Affair

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2014, 12:44:08 pm
content: Thanks, fixed

author: macboy
author_rank: Super Contributor
timestamp: April 08, 2014, 01:22:49 pm
content: Quote from: forrestc on April 08, 2014, 12:16:24 amKeithley 2001 can display DC, AC, and Frequency simultaneously. The update rate of the display is slowed down since the instrument needs to cycle through the different measurements each time. AC measurement can be set to DC coupled so that AC+DC true RMS is measured. Peak voltages can also be measured instead of RMS, and crest factor can be displayed. It is a very versatile meter. My 2001's are flat (+-0.1 dB) in AC to about 4 MHz and and -3 dB at 7 MHz. Very few meters have better AC bandwidth (only the venerable 3458A comes to mind).The 2001 is an older design, no fancy color LCD, just a nice VFD. It is still available new, but is very costly (>$4000!!). It is common enough on the used market, but even used, it goes at a premium since it is a true 7.5 digit meter.There is no reason not to use two different meters, one for DC and one for AC. In fact, this may be the best solution since it may give you better AC accuracy. Consider that the AC ripple is usually << the DC offset. If using a single meter, you can imagine that the meter will need to either change range when measuring the AC portion of the signal, or sacrifice accuracy and resolution by not changing range. The former will likely result in clacking relays, and the latter is entirely undesirable when AC << DC.

author: robrenz
author_rank: Super Contributor
timestamp: April 08, 2014, 01:52:46 pm
content: Quote from: macboy on April 08, 2014, 01:22:49 pm8846A has 1µV ACV secondary display resolution on the 1V DCV range and 10µV ACV secondary display resolution on the 10V DCV range. No relay action involved.

author: willb
author_rank: Regular Contributor
timestamp: April 08, 2014, 02:19:52 pm
content: Quote from: forrestc on April 08, 2014, 12:16:24 amFluke 45 as previously suggested. It's a little slow when using the dual displays, but it works, will do ACV + Freq, ACV + DCV, etc, and can be easily found for under 200$.

author: dr.diesel
author_rank: Super Contributor
timestamp: April 08, 2014, 07:06:14 pm
content: If you don't need the resolution of the 8846A could you almost buy two of the HMC8012s for the price.The Hameg is also slightly more compact, if your cramped on available space.