New Keithley DMM6500 and now DAQ6510

[KungFuJosh]

Almost all of my test gear is switched off on a rackmount PDU. I only have a hard switched PSU (SPD3303X), and my GPSDO always connected to unswitched outlets.

That said, my DAQ6510 is not louder than my Keysight or Siglent DMMs...except the SDM3055X-E that doesn't have a fan.

[slavoy]

Got reply from the local distributor, it's going to be sent for repair

[Kleinstein]

I think they should add the transformer hum to the quality control - it is just stupid to get a sizable fractions back for exchange of the transformer and if taking it serious a new calibration.

[skander36]

Maybe Keythley does not have enough tradition to check the transformers for other voltages networks ...  Im joking ...
Transformers are made in Dominican Rep. where the voltage is also as in the US, 110-120V AC. For sure they are not testing thoroughly enough at the actual voltages across Europe which is now over 240V frequently. This is the reason for most US users does have problems with the hum.
But this issues is over 5 years older and Keythley should've been addressed until now with a new designed transformer.

[Hydron]

You'll get a free calibration out of it at least. Mine came with full data too (and they dug up the data for the prior calibrations when I asked - worth trying to get the data as that way you might get an idea of drift).

[HighVoltage]

Maybe someone that has a DMM6500 with hum can test at different line voltages with a variac transformer to see if the hum really is voltage depending. Maybe some just have a bad transformer.

My DMM6500 was one of the first units on the market and works well without hum.

[skander36]

Maybe someone that has a DMM6500 with hum can test at different line voltages with a variac transformer to see if the hum really is voltage depending. Maybe some just have a bad transformer.

My DMM6500 was one of the first units on the market and works well without hum.

Mine had hum from the beginning but after switching to 240V hum was considerably reduced (but not completely) so I can ignore now. Anyway is my only device with linear power supply on my desk which have hum (so little as it is now).

[kmoonwalker]

Almost all of my test gear is switched off on a rackmount PDU. I only have a hard switched PSU (SPD3303X), and my GPSDO always connected to unswitched outlets.

That said, my DAQ6510 is not louder than my Keysight or Siglent DMMs...except the SDM3055X-E that doesn't have a fan.

I got one unit of DMM6500 from customer to add it into his workflow - it was few months after it was released back then.

My remarks were as I had also 34465a from him and other stuff that 6500 had most annoying fan noise of everything I had back then and it was really louder than 34465a. As for the hum changing setting to 240V decreased transformer hum considerably thou for my personal preferences as I usually have very quiet at home it was too loud (but I am sensitive to that so for most of people this maybe not an issue at all). 34465a I got recently has even more quiet fan than that old one I had (I compared them both side by side yesterday as it went that I had some maintenance work there).

For me one of the issues with DMM6500 is that they use very thin fan.

I seen some of 6500 modded in a way that they put inside thicker noctua fan and some even further went into drilling set of holes for second fan next to that one to have more quiet and similar airflow.

From what I heard over the years there seems to be a very wide distribution regarding that transofomer hum and fan noise in this model.

[Martin72]

Maybe someone that has a DMM6500 with hum can test at different line voltages with a variac transformer to see if the hum really is voltage depending. Maybe some just have a bad transformer.

The humming noise is almost certainly dependent on the voltage.
Audible humming can occur if:
-The windings oscillate, i.e., they are not vacuum-impregnated.
-The windings are insufficiently impregnated.
-Their oscillations are transmitted to the core and the core is not mechanically decoupled from the housing.
-There are DC components in the mains that drive the core into saturation.

The pictures I found of the DMM6500 transformer suggest that its windings are impregnated.
https://xdevs.com/doc/Keithley/DMM6500/lukier/framexfr.jpg

This may no longer be the case with newer models for cost reasons.
Either way, using the image as a reference, you could place foam rubber tape between the coils and the base plate.

[kmoonwalker]

I often see on transformers made for things friends are manufacturing that you get like 80% of very well made and from rest you select that half that can stay and rest is sent back to factory. If they fix the problem on new runs we stay with manufacturer - if not we research new one till we have it on our "acceptable" level.

Nowadays one could think they should make transformers way better than in the past but this is usually not the case sadly :/

They only look way better during visual inspection but it is deceiving...

[thm_w]

I think they should add the transformer hum to the quality control - it is just stupid to get a sizable fractions back for exchange of the transformer and if taking it serious a new calibration.

99.99% of these are going into office labs or racks where no one would care, ambient noise is far higher. Probably cost them more to have someone sitting there testing each unit.

The 6500 fan is the quietest instrument fan I have on this desk by far, the fact that people are complaining about that tells me how sensitive their hearing and how quiet the ambient environment is. I get the annoyance, but at that point I would mod the unit (unplug or replace fan).

[exe]

Does the hum changes when the unit is powered on?

Asking because, afaik, trafos often a little bit under-winded to increase their efficiency under load and decrease costs. The downside is, under light load or increased input voltage they got overwhelmed. Source: https://sound-au.com/xfmr.htm#s31

[Hydron]

As exe alludes to, one of the issues here is that the transformer is always on, even with the meter off (soft-off switch ) - so it's in light-load regime when off and that makes the noise worse.

I did look at hacking something up that would disconnect the transformer when the meter was off, but run the digital section off a 5V switchmode supply so that the power button still works (and sense when it turns on to switch back to transformer opteration - i think there will be a pin on the communications plugin connector to allow this), but the fixed unit has acceptably low hum when off and the effort didn't seem worth it just to save 2, maybe 3W of standby power loss.

I might have another look at the fan options - didn't realise that a thicker fan would fit, currently I just have a dropper resistor in series but that does reduce airflow (compared to a thicker fan which is likely quieter at the same airflow as the original). The lower airflow doesn't seem to affect performance though at least in my non-industrial environment, I get very fast warmup and exceptionally low tempco on the 10V range (as in I can't measure it, is way better than my Advantest R6581T).

[JimKnopf]

@HighVoltage I did a test with a transformer.

I bought the DMM6500 in 2020 and never touched the fuse setting on the backside. It was set to 220V by factory. My mains voltage is at around 235 V.

Since i have a surface microphone and a EA-STT 2000B adjustable transformer, i run a test.

First one with original factory setting (220V) on mains voltage at 235V. Clearly audible humming. It's not anoying me because even the fan of my SLS2 laptop is louder.

I connected the DMM6500 to my EA-STT 2000B, starting at 220V and slowly increased the voltage. At the beginning, the humming was barely audible. At 225V it was increasingly audible. You can see it in the screenshot, after it passes 230V, the humming was nearly at max noise level.

For the last test i set the DMM6500 to 240V on the backside and connected it again to mains voltage at 235V. The humming was barely audible (for me). When powering on, the fan dominates the noise. After the relais clicking, the fan runs a bit faster, it's visible in the screenshoot.

I recorded the humming with audacity.

[KungFuJosh]

I did look at hacking something up that would disconnect the transformer when the meter was off

This might sound crazy, but hear me out...

Have you considered using a power strip with a switch on it? Or a smart outlet or smart power switch?

My Hioki LCR sounds like a jet engine, so I have it on a smart outlet and tell the robot to "turn on LCR" when I need to use it. I like the Kasa HS300 since you can have different things switched individually.

Thanks,
Josh

[HighVoltage]

Hallo JimKnopf
What a nice test you did.

Since the transformer’s flux density is proportional to the voltage / frequency the magnetic core gets closer to saturation at higher voltages.
When the core reaches saturation, the magnetizing current rises, producing larger flux oscillations and stronger magnetic forces which causes a louder hum. Also, the harmonics could influence the harsher hum sound. The Magnetostriction always depends on the square of the magnetic flux density. That is probably why the hum increases so suddenly. Once the core has reached or is close to saturation, the hum should be 100 Hz on a 50 Hz mains.

It seems your test confirms that the transformer has a design problem and maybe on some units the hum is not showing up because ob better lamination, I guess.

[slavoy]

Does the hum changes when the unit is powered on?

It’s hard to say, because the fan drowns everything out. The hum definitely remains because it can be heard. I’ve just checked the 220/240V settings again, and there’s a reduction at 240V with mains supply at 237V at the moment. The casing strongly amplifies the resonance. If I removed the rubber covers and placed it on the shelf, the whole thing would probably start resonating even more.
Also when switched off, it consumes 4–5W, checked with a cheap meter.
Again, I can live with the fan, maybe replace it myself sometime later. The transformer is a much bigger issue.

[kmoonwalker]

you can try to put on top some weight like 2-3 kg so it could "calm" down a bit the chassis vibrations (but transformer will be audible regardless)

there is always the possibility that someone not tightened transformer screws properly or one can add dampening pads and it is resonating due to this

you can also try without rubbers - sometimes it amplifies but other times it can kill the vibrations

[KungFuJosh]

you can also try without rubbers

Eh, not recommended. 

[Hydron]

you can also try without rubbers

Eh, not recommended. 

It is quite a delayed result, but typically results in dramatic noise increase for about 20 years.

Back to transformers - I think I did check saturation (looked at current waveforms) before and after I had mine swapped and the new one was no better than the old in that respect, but the noise was way down, so the "good" units clearly don't fix it (that'd probably need a redesign to increase turn count) just mask it's effects.

As for controlling the power, I do have a bunch of home automation including smart power sockets (either zigbee or wifi running tasmota, so I have real control and don't send my network details to bezos or a random Chinese server), but as I'd like to not need to talk to my multimeter to turn it on I can't do it that way. I might in the future rig up some sort of bench level power control for when I need nothing running though.

[KungFuJosh]

As for controlling the power, I do have a bunch of home automation including smart power sockets (either zigbee or wifi running tasmota, so I have real control and don't send my network details to bezos or a random Chinese server), but as I'd like to not need to talk to my multimeter to turn it on I can't do it that way. I might in the future rig up some sort of bench level power control for when I need nothing running though.

My bench stuff is racked now, and I have rackmount power supplies controlling everything. So there's an easy to access switch up front. I have the Juice Goose JG11-15A (they also have a 20A version). I like them because they have lots of outlets, including an unswitched outlet on the front and another one on the back. Both racks are plugged into a filtering sinewave UPS.

The only reason I used the smart switch for the LCR is because the hard switch is on the back of the LCR, and I'd rather talk to it than give it a reach around.

[slavoy]

Well, I couldn't help myself and tear it down to see if the transformer is sealed. It is indeed. Didn't touch any further.

When I started assembling it, I noticed a nice detail. I really appreciate how that board jumps along with the beautiful Fluke resistor when switching to the rear terminals 
https://www.youtube.com/shorts/PZ8wdn_FRVQ
I also like the mounting of this heatsink, which touches the PCB with its edges.
https://www.youtube.com/shorts/kXtIA7wW2GA
What rhymes with "make it cheaply"?

[bateau020]

For the board flex, there are 3D printed "customisations". Look at post #1450 here (page 30).

[TUMEMBER]

Well, I couldn't help myself and tear it down to see if the transformer is sealed. It is indeed. Didn't touch any further.

When I started assembling it, I noticed a nice detail. I really appreciate how that board jumps along with the beautiful Fluke resistor when switching to the rear terminals 

I also like the mounting of this heatsink, which touches the PCB with its edges.

What rhymes with "make it cheaply"?

Oh well, great! This is a test of the functionality of multilayer board connections conducted live by the end user.  "pyknie czy nie pyknie"-"Will it work or not?" is the "Russian-giant-not-a-looter"( ruskie* CCCP-gniotsia nie łamiotsia" version.
It makes you want to "throw up" - "What the fuck is this supposed to be?" And in the metrology department people are "fighting" about the effect of a butterfly flying over resistors and changing their characteristics and measurement values.

[kmoonwalker]

Oh well, great! This is a test of the functionality of multilayer board connections conducted live by the end user.  "pyknie czy nie pyknie"-"Will it work or not?" is the "Russian-giant-not-a-looter"( ruskie* CCCP-gniotsia nie łamiotsia" version.
It makes you want to "throw up" - "What the fuck is this supposed to be?" And in the metrology department people are "fighting" about the effect of a butterfly flying over resistors and changing their characteristics and measurement values.

regarding metrology my first remark (that I think was not mentioned?) is that how much such strong transformer vibrations could affect our precious ppms ;P

on the other hand if it can measure so well in such conditions it is indeed a splendid design but why force it to work in such horrible conditions heh

@KungFuJosh
the one I had to evaluate I actually had without rubbers and I put on it some weights (I think 1,5-2 kg or a bit more) and it helped greatly back then with chassis resonance.