BM235 Frequency

[tangram]

Just bought a second-hand Fluke 85 III multimeter.  Once I got it home I was keen to make sure it's working properly and, of course, I broke out my trusty EEVBlog BM235 multimeter to use as a reference.

I'm very happy that, in ranges, the Fluke is almost digit for digit giving the same results as the BM235.  All but one!. 

Using a Siglent signal source, I can see the Fluke measuring a DC or AC frequency up to about 500Khz.  I can't get the BM235 measuring frequency at all... not a sausage.

It's no biggy... I've never even thought to try this trick, but is it because there's a problem or, and I'm guessing this is option has a high degree of probability, am I misunderstanding what the Frequency Counter of the BM235 is actually capable of measuring, i.e. it's not designed to read frequencies at low voltages?

[Karlo_Moharic]

Try to measure AC mains frequency  , you should have enough of the amplitude

[tangram]

BINGO!

Into the mains, with all safety precautions of course, and 242v... switch to Hz and....................... 49.95 Hz. 

Many thanks, Karlo.   

[Karlo_Moharic]

No problem

[JS]

Hi tangram!

I saw the same thing as you with the BM235, fine on mains level (even on VFD, which I use a lot in industrial app) but it's supposed to work on lower levels, but I couldn't make it work. When you switch to freq it tells you the voltage level it's working on, so if you start with a smalish signal it tells it's on 6V range but it doesn't display freq. Have you found a solution or something about this? It could come handy once in a while to check a thing or two.

JS

[HKJ]

I have not seen any problems with the BM235 and frequency (Review: https://lygte-info.dk/review/DMMBrymen%20BM235%20UK.html), it requires less than 0.1Vrms to count. The signal must include zero crossing!

[JS]

I have not seen any problems with the BM235 and frequency (Review: https://lygte-info.dk/review/DMMBrymen%20BM235%20UK.html), it requires less than 0.1Vrms to count.

Nice to know, I should look further...

The signal must include zero crossing!

Why??? but why??? couldn't they make it AC coupled?? I guess I should make it ac coupled outside the meter to measure... DIY AC coupled probes?? Time to add a cap inside a probe and label outside, for me it's quite useful to check PWM frequencies and general µC pin toggling which doesn't include zero crossing, maybe that's my issue.

JS

[HKJ]

The signal must include zero crossing!

Why??? but why??? couldn't they make it AC coupled?? I guess I should make it ac coupled outside the meter to measure... DIY AC coupled probes?? Time to add a cap inside a probe and label outside, for me it's quite useful to check PWM frequencies and general µC pin toggling which doesn't include zero crossing, maybe that's my issue.

Many multimeters requires a zero crossing. I have not been counting, but I believe that significantly more than 50% of the meters I have reviewed requires it.
Some meters has a offset on the detection (between 1 or 2 volt), this means they will work with most pwm signals and some meters has a capacitor on the input.

[JS]

Many multimeters requires a zero crossing. I have not been counting, but I believe that significantly more than 50% of the meters I have reviewed requires it.
Some meters has a offset on the detection (between 1 or 2 volt), this means they will work with most pwm signals and some meters has a capacitor on the input.

I'll check with a cap in my next debugging and come back...

JS