Products > Test Equipment
DMM with THD capabilities
pope:
Hi,
I'm into audio electronics and I was wondering whether there are any DMM out there that can also measure THD. AFAIK, keithley 2015 and 2016 can do THD but can you recommend some newer and hopefully cheaper meters?
Having said that, I do have indeed an audio interface and some software to do THD (or THD+N) measurements but I would like to be able to measure the THD on different stages of a circuit and the audio interface isn't always the best solution due to higher voltages. Also, although I have a brymen 869s meter, GAS is calling for a benchtop meter :D
Kleinstein:
THD is not a usual DMM feature. This is more something for a DSO with build in generator. However these are suitable only for rather high THD (e.g. > 0.5%).
An audio interface / sound card is more like the suitable instrument. For the higher voltages (power amplifier out) it may need a suitable probe / divider and protection.
HighVoltage:
The Keithley Series 2000 is also THD capable!
"The 2000 THD series of Keithley Instruments are "Total Harmonic Distortion" analyzers, which are used for audio analysis and distortion measurements. The frequency range starts from 20Hz to 20kHz and a built-in low distortion sine wave Generator provide the adjustable signal for testing amplifier stages or speakers for distortion. Thus, for example in the production of mobile telephones, the microphone, the amplifier and the speaker part may be tested with this single device. The full digital multimeter part was taken from the model 2000 and allows measurements of 100 nV to 1000V."
Berni:
Even on that Keithley 2015 the THD feature doesn't go all that low, so likely not very useful for modern audio stuff with very little distortion. (Unless you are working on old tube amps?)
You can do a similar thing using an oscilloscope and FFT, but most scopes don't have the dynamic range required to make useful measurements on very low distortion stuff.
Unfortunately only dedicated signal analyzers or sound cards have the dynamic range to pull this off. You can still create a buffer circuit with input dividers and protection, so you adapt the dangerous high level signals into the input of one of these.
AVGresponding:
--- Quote from: HighVoltage on January 03, 2023, 12:51:51 pm ---The Keithley Series 2000 is also THD capable!
"The 2000 THD series of Keithley Instruments are "Total Harmonic Distortion" analyzers, which are used for audio analysis and distortion measurements. The frequency range starts from 20Hz to 20kHz and a built-in low distortion sine wave Generator provide the adjustable signal for testing amplifier stages or speakers for distortion. Thus, for example in the production of mobile telephones, the microphone, the amplifier and the speaker part may be tested with this single device. The full digital multimeter part was taken from the model 2000 and allows measurements of 100 nV to 1000V."
--- End quote ---
You're misunderstanding what the manual is saying. By "2000 THD series", they mean any 20xx THD meter, which is two. The 2015 THD and the 2016 THD. The 2000 is just a DMM, and does not have the internal sine generator and THD measurement circuitry. The THD meters are a LOT heavier because they have a LOT more internally going on.
Yes, I am speaking from personal knowledge; I have a K2000 and a K2015THD, the THD meter weighs about half as much again as the plain DMM.
The OP doesn't mention a budget, and idk what the market is like in Greece, but I was patient and paid ~£400 for my K2015THD, with a fairly recent cal.
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