An modern NO True RMS DMM?

[GarySnail]

I’ve on the search for something unusual.   
I’m looking for an Benchtop DMM that isn’t TRUE RMS. I’m interested in average rectified value (ARV) and the formfactor of the Signal.

I want to test Current Transformers and see the Result in ARV because RMS falsifies it.
The CT’s will be in saturation therefore my output signal will be distorted. With the ARV it’s still comparable.

I’ve checked most of the bigger manufacturer but no one did provide information, if it’s possible to show the value.
Only the Keithley DMM6500 shows in one of its Sample pictures an AVG value. But it is mAmps and I’m not sure if it’s the correct average.
I know that lots of old multimeters use exactly this way to calculate the RMS value, but I would like to integrate it in my system so an USB or any other modern Interface would be nice.

Any suggestions?

[001]

Is it sort of trolling?
Use scope for amplitude readings

[GarySnail]

I’d like to automate the process, therefore its not an option to look on an scope every time.
All I need is a value which I can compare to the min/max that is given.

[HKJ]

I do not know of a bench meter, but a high end hand held meter:
Kyoritsu KEW1062 or YOKOGAWA TY720 it is basically the same meter.

It can be switches between mean and RMS reading.

[001]

I’d like to automate the process, therefore its not an option to look on an scope every time.
All I need is a value which I can compare to the min/max that is given.

It is basic function for DSO

[exe]

RC-filter?

[pigrew]

Is this for an automated test setup? If so, you can program a computer to get data from a USB oscilloscope, and then do processing on the computer.

You could also build a precision rectifier circuit and measure its output in DCV mode.

What voltage and frequency (ranges) are you needing to measure? With what accuracy?

I wonder if a low-end DMM from China would be what you need, but getting calibration certs would be difficult.

The Keysight U2741A didn't mention True RMS in its datasheet, not sure if it is or not.

[Fungus]

I’d like to automate the process, therefore its not an option to look on an scope every time.

No need. Modern DSOs have USB/Ethernet connections so you can hook them up to a PC and automate everything they do.

It's usually an ASCII plaintext interface.

[jfiresto]

If you can accept a handheld meter with a 300–350 hour battery life while logging, the the B&K 390A is "average sensing, RMS indicating". It has a pretty much standard, USB interface with a well defined protocol. It can also capture the voltage or current min/max-values-so-far that have lasted longer than 1 ms. B&K's support is very good.

Should you need it, I can send you a Python utility I have written, that collects its data. i have run it, so far, under OSX, Windows and RPi Linux.

[Fungus]

If you can accept a handheld meter with a 300–350 hour battery life while logging...

You could run it off a power supply if it's going to be fixed to a bench and battery life is an issue (via a couple of wires in the back).

[CDaniel]

I doubt that B&K390A , or similar crappy 1KHz bandwidth multimeter is any good , knowing that the current waveform is highly distorted , so even at 50Hz the harmonic content is very high ...

You have to use an 100KHz true rms meter that can measure average up to aprox 20KHz , average is lower bandwidth , like recomanded in reply #3 , or there are similar benchmeters .

[KedasProbe]

The average of the DMM6500 is sum/count (what you would expect)

But can't you just get the samples and calculate what you need.
DMM6500 also has scripts so you would be able to do it standalone.

I don't know if the quality of the samples will be good enough for you at max samples speed.
but I can do a test though and give you the samples, so you can decide.

Script:

sum = 0
for index = 1, defbuffer1.n do
   sum =sum + math.abs(defbuffer1.readings[index])
end

if defbuffer1.n > 0 then
   display.settext(display.TEXT1, sum / defbuffer1.n .." V")
   display.changescreen(display.SCREEN_USER_SWIPE)
end

[macboy]

Keithley 2001 (& 2002) can display AC as True RMS, Average, or Average calibrated to RMS (reads average value but adjusts to give equivalent to RMS value of a sine wave). Bandwidth is several MHz. This last option is only available on certain later firmware, but a workaround is to use the math function to scale the reading.  Coupling can be either AC or DC, so you can measure a signal with DC offset. I would think that the DMM6500 is similar. I'd suggest to download and read the Keithley DMM6500 operator manual. Keithley manuals are usually very good at fully describing every feature.

[schmitt trigger]

I agree with other posters that a modern DSO is the way to go, even for automated tests.

They all now have some sort of serial comms, and can be set up for automatic readings of many parameters.

Otherwise as other poster mentioned, build a precision full wave rectifier with a pair of opamps, feed to any DC meter, and there you have it.

[ogden]

I agree with other posters that a modern DSO is the way to go, even for automated tests.

AC (amplitude) accuracy of most generic/8-bit DSO's are around 3% while 4-digit DMM's have 1% or better. I agree with those who suggest to manufacture DIY-rectifier for DMM in DC mode.