The mV relative mode statements in the manual makes no sense to me. If the zero calibration point is off far enough that you need to REL the meter before taking a measurement, then the final reading will be off as well. If you REL out noise/interference, same issue.
I believe the reason for using REL in the lowest mV range is to compensate for any temporary offset drift (usually) caused by temperature variations. In DC mV mode the signal passes through PTCs which can exhibit thermocouple behavior - then there’s i.e. also possible drift in the pre-amp and ADC.
In AC mV mode the signal has more or less the same path as DC but is then AC coupled right before the AD8436 RMS converter - so here it’s really only if the converter exhibits any drift you’d want to use the REL to cancel it out.
This description is for the 121GW but many other DMMs has much the same problem.
Don't blindly trust one DMM.
This is a key point. If I had (besides budget) more room, I would get a Keysight 34465 bench meter and a good handheld DMM, say Fluke 287/289.
(Btw, the Flukes are here in Europe twice the price of the US market prices.)
I am interested in low voltage AC (down to a few mV) for some audio connected measurements.
Ideally, I would find a handheld DMM with the accuracy of the 34465, but this does not exist.
Perhaps a dedicated AC mV meter would be a better option - I don’t really have any specific to suggest though.
When I needed to measure sub mV Audio signals I built an external AC amplifier based on the OP37 opamp. Placed it in a battery powered small shielded box I could attach directly to a handheld DMM. I could set the amplification to 10, 100 or 200X and here the frequency response was perfectly flat 20Hz - 20KHz and a bit beyond. I don’t know if any such device exists ready to buy though.
When I needed to measure sub mV Audio signals I built an external AC amplifier based on the OP37 opamp. [...] I don’t know if any such device exists ready to buy though.
I have never soldered before, so I would have to buy it - if it is for sale.
Your approach sounds somewhat similar to the eevblog uCurrent, but I am not sure if it measures uV AC.
Besides, the uCurrent is out of stock everywhere.
Please let me know if anyone has an idea where to get a (reasonably priced) AC amplifier to use with a DMM.
Hi All, this weekend I blew the 400mA 600V fuse. I'm in the US, and Dave's fuse pack would take some time to get here. I see lots of 600V 500mA fuses available, not so much with the 400mA. Could I safely use a 500mA fuse instead?
The range is 500mA, so the 500mA 600V fuse is fine, if it has a FF rating (Fast) and a high breaking capacity (10kA).
6x32mm, rated for AC/DC (UL248-1)
Stick to good brands, like Littelfuse, Cooper Bussmann or Siba if you can, otherwise examine the datasheet carefully for compliance.
The manual recommends cryptically ASTM HV610.0.4 400 mA (600V) or HV620.0.4(1000V) A/500 mA current input fuse (sic)
Stick to good brands, like Littelfuse, Cooper Bussmann or Siba if you can, otherwise examine the datasheet carefully for compliance.
The manual recommends cryptically ASTM HV610.0.4 400 mA (600V) or HV620.0.4(1000V) A/500 mA current input fuse (sic)
Ah okay, well if 1000V fuse is acceptable then there are many 500mA to choose from. Thanks.
I have Dave's fuse pack on order, but that will take 15 days and I can't wait that long to get this back into service. I should have stocked up on fuses for it, but it never occurred to me they would be hard to find on short notice. In the meantime I'll use the one I ordered and be super careful not to screw up again. Maybe the international postal Gods will smile on me :-)
Stick to good brands, like Littelfuse, Cooper Bussmann or Siba if you can, otherwise examine the datasheet carefully for compliance.
Beware of fakes on ebay and other places. Because of the very high potential margins on these, the market is awash with fakes.
Hi all,
I received my 121GW today. I went to check the firmware and I see v2.04 is the highest listed on the 121GW firmware page, but the start screen on the DMM shows v2.05. Is this an error and I should flash 2.04, or is 2.05 real and just not listed yet?
Thanks.
Hi all,
I received my 121GW today. I went to check the firmware and I see v2.04 is the highest listed on the 121GW firmware page, but the start screen on the DMM shows v2.05. Is this an error and I should flash 2.04, or is 2.05 real and just not listed yet?
Thanks.
Probably not listed yet. Check the contents of the microSD card. If you see a file named EEVBlog.bin, share it with us.
Alexander.
Hi all,
I received my 121GW today. I went to check the firmware and I see v2.04 is the highest listed on the 121GW firmware page, but the start screen on the DMM shows v2.05. Is this an error and I should flash 2.04, or is 2.05 real and just not listed yet?
Thanks.
I don't have have 2.05, have asked Kane what the deal is.
I have new stock on the way soon, don't know what version they will have. I can only presume that you bought it from Welectron and they somehow have a newer version firmware.
Hi all,
I received my 121GW today. I went to check the firmware and I see v2.04 is the highest listed on the 121GW firmware page, but the start screen on the DMM shows v2.05. Is this an error and I should flash 2.04, or is 2.05 real and just not listed yet?
Thanks.
I don't have have 2.05, have asked Kane what the deal is.
I have new stock on the way soon, don't know what version they will have. I can only presume that you bought it from Welectron and they somehow have a newer version firmware.
Yes, it is from Welectron.
Thank you.
I now have v2.05
They changed the low pass filter curve to better match the performance of the Fluke 289, which I guess they are using as a sort of reference.
And yes, this version was shipped to Welectron.
Flashed without incident.
I now have v2.05
They changed the low pass filter curve to better match the performance of the Fluke 289, which I guess they are using as a sort of reference.
And yes, this version was shipped to Welectron.
is that the only update??
I now have v2.05
They changed the low pass filter curve to better match the performance of the Fluke 289, which I guess they are using as a sort of reference.
And yes, this version was shipped to Welectron.
is that the only update??
Yes. That is the only change they said was made.
Also got mine from electron today with 2.05. Also the yellow shim have been removed?
Does it always comes without probes? I thought it’s either Brymen or UEI probes.
Cheers
Also got mine from electron today with 2.05. Also the yellow shim have been removed?
Yes, the shim was only for the first several thousand PCB's that had the wrong thickness.
Does it always comes without probes? I thought it’s either Brymen or UEI probes.
I don't have control over what Welectron sell, but Kane's standard FOB quote is without probes. If the distributor wants probes then they have to order them as a separate line item.
By default Welectron checks the box to include the probes when you hit the 121GW page, but you can uncheck it.
I have two 121GW units that came with shims. I removed it from both and have had zero issues. Perhaps after things wear it might be needed.
Also got mine from electron today with 2.05. Also the yellow shim have been removed?
Yes, the shim was only for the first several thousand PCB's that had the wrong thickness.
Does it always comes without probes? I thought it’s either Brymen or UEI probes.
I don't have control over what Welectron sell, but Kane's standard FOB quote is without probes. If the distributor wants probes then they have to order them as a separate line item.
Thx for the reply. I didn't know they aren't stock included.
By default Welectron checks the box to include the probes when you hit the 121GW page, but you can uncheck it.
I have two 121GW units that came with shims. I removed it from both and have had zero issues. Perhaps after things wear it might be needed.
Yeah, I thought there were some included, so I unchecked it
. Got myself some Fluke Probes now, maybe have to shorten the banana plugs a bit but otherwise they work fine.
Yeah, I wanted to remove them to avoid issues and found out they aren't there anymore.