Budget multimeter recommendations?

[Corky34]

Not wanting to necro watercooled thread from 9 years ago and wanting to have a feature that I'm not sure comes with all multimeters I'm putting my trust in you guys and girls. The extra feature I'm looking for, beyond what i assume is typical, is measuring a PWM signal, would i be right in saying that's frequency.

I watched the video linked in the above thread from EEVblog and as a hobbyist i got a bit lost and it's from 10 years ago so I'm not sure how relevant it still is, what would be great is if someone could say buy this, it's under £50, you can use it to measures a PWM signal and most other DIY jobs around the house.

[ik9000]

signing in as interested too. I ended up buying a lamptron sm436 fan controller to monitor pwm or rather convert it to rpm for me. I power it off a standalone DC supply via some crocodile leads into a molex cable.

[CAT-THE-FIFTH]

I remember a while back checking Ebay,and found a pair of Brymen ones really cheaply.It appears people were after more famous brands like Fluke(which are fantastic),so you just need to do some research. EEVBlog YT channel and website is a good place to start(Brymen was one of the brands mentioned).

If you want to spend less,its worth checking out their forums too:
https://www.eevblog.com/forum/beginn...-i-should-buy/
https://www.eevblog.com/forum/review...d-multimeters/

Its a treasure trove of information.

[ik9000]

FWIW my mutlimeter is a Aidetek VC99+ and it's great (and affordable). I've just noticed it has a Hz setting, not sure if that will check pwm pulsing for rpm, however I have hooked it up to the lamptron to log the DC volts and it does seem to show the average V when the unit is supplying pwm signal to the fan. You get a bit of a drift +/-0.5V but it's easy enough to work out the net average.

I can't see it on there anymore but this one looks nigh-on identical: https://www.amazon.co.uk/Auto-Rangin...dp/B00EYYJRC0/

Give me the evening and I'll have a play re the pwm/rpm side of things. Not sure if it will play ball only having one lead connected though to the pwm header pin. Maybe the 2nd lead just needs to go to ground idk?

[Corky34]

IDK know they had a forum too, thanks Cat.

FWIW my mutlimeter is a Aidetek VC99+ and it's great (and affordable). I've just noticed it has a Hz setting, not sure if that will check pwm pulsing for rpm, however I have hooked it up to the lamptron to log the DC volts and it does seem to show the average V when the unit is supplying pwm signal to the fan. You get a bit of a drift +/-0.5V but it's easy enough to work out the net average.

I can't see it on there anymore but this one looks nigh-on identical: https://www.amazon.co.uk/Auto-Rangin...dp/B00EYYJRC0/

Give me the evening and I'll have a play re the pwm/rpm side of things. Not sure if it will play ball only having one lead connected though to the pwm header pin. Maybe the 2nd lead just needs to go to ground idk?

Thanks for the link, I'd be the worse person to ask about if it needs a GND, i guarantee i know less than you.

I'll probably buy one and blow myself up within a week.

EDIT: So having educated myself a bit more i was thinking it maybe better spending a bit more to get an oscilloscope multimeter, I'm not entirely sure though, what's peoples thoughts on this? https://www.amazon.co.uk/Digital-Osc.../dp/B07YSNFRVM

2nd EDIT: I've done what i always do when trying to learn about something, I've ended up totally confusing myself.

[g8ina]

https://www.amazon.co.uk/Neoteck-Mul...2&s=diy&sr=1-3

That one looks OK to me, Id buy one if I needed the functions you mentioned, 100Hz FS up to 30MHz Nice.

[DanceswithUnix]

What are you trying to do with PWM?

If you want to check duty cycle, then you probably do want a 'scope not a multimeter. Just checking frequency of a PWM signals isn't generally that useful.

Edit: That scope multimeter looks pretty slow, so it might work for very low frequency PWM signals for things like servo or motor drive but any high frequency PWM outputs it probably won't see.

[Corky34]

The intention was to check what i suspect maybe some fake PWM headers on a motherboard and then keep it around for general DIY stuff in the future. However after having spent the last couple of days reading it seems i underestimated how complex (at least for me) such a thing is, I'm thinking i maybe better off getting a multimeter like the one g8ina and ik9000 kindly linked to and then a separate cheap'o scope, i was looking at those DIY scopes like the Kuman DSO 138 as it would make for a nice project/practice but I'm not entirely sure if probing a 12v PWM header would be too much for it as I'm not entirely sure what some of the specs mean, like does 5V/Div mean it can only measure up to 5v or that each line/division on the screen would be 5v so with 10 lines you'd have a 25v +/- range.

[ik9000]

that oscilloscope you linked to isn't very good. The reviews point out you can't adjust the frequency axis in the display which is kind of important for viewing waveforms IMO. You're better off getting a bench unit if you can't find a handheld that lets you do that.

[Corky34]

Yea i wasn't expecting it to be at that price. I wish my level of understand was enough to know why I'd want to know the frequency, i wasn't expecting what seemed like such a simple thing (those pretty plots of waveforms) to be so complex, I'm feeling a bit like I've fallen down a rabbit hole.

[g8ina]

Nice scope for sale in Faceache :
https://www.facebook.com/marketplace...93647971005902

[DanceswithUnix]

From a quick Google, if all you want to look at is PC fan headers then they only work at around 25KHz. That's unfortunate, as it's just a bit too high to be able to slap a couple of resistors across it and feed it into a sound card line input.

Still, in 'scope terms 25KHz is nothing. For a simple visual "Yeah, that's a PWM signal" you could get away with sampling at 10 times higher, so that cheap multimeter scope you linked earlier that samples at 200KHz is just capable.

I note looking at it there is a setting for "Frequency/Duty Cycle" so it looks like it will even try and tell you what percentage of drive the fan is getting.

The frequency measurement should also be handy for measuring fan tacho pulses being sent back from a PWM fan.

So that looks like it would fit the bill, or at least something like it given it says on the page it would turn up some time in March so I guess that is arriving direct from China.

, like does 5V/Div mean it can only measure up to 5v or that each line/division on the screen would be 5v so with 10 lines you'd have a 25v +/- range.

You read it like graph paper, so 5V per division means 10 divisions is 50V. One of the dials on a traditional scope is a Y offset, so you can decide which division is 0V allowing you to do ac or dc waveforms.

[ik9000]

A lot of the handheld cheap oscilloscopes I looked at the other day don't appear to allow offsetting the Y axis nor altering the axis scales independently (to expand frequency scale for example)

[Corky34]

Nice scope for sale in Faceache :
https://www.facebook.com/marketplace...93647971005902

That's a bit more than i was hoping to spend, it was only a couple of days ago that i thought £50 would get me a DMM with the ability to see if a PWM fan header is actually using PWM or cheating by lowering the voltage.

A lot of the handheld cheap oscilloscopes I looked at the other day don't appear to allow offsetting the Y axis nor altering the axis scales independently (to expand frequency scale for example)

Embarrassingly i wish i knew why i would or would not want that, even though I've spent the last couple of days reading up i still feel like an idiot.

I'm very much a learn by doing sort of person so I'm going to buy the VC99 you linked to earlier and the updated model of the DSO138, when it's in stock in the UK that is because not knowing if i had to pay import fees would trigger my anxiety, that way i can learn how to use a DMM and practice soldering while i build the DSO and not have to worry to much if i get something wrong.

So grateful for everyone's input, wasn't looking forward to second guessing myself for weeks.

[matts-uk]

The intention was to check what i suspect maybe some fake PWM headers on a motherboard and then keep it around for general DIY stuff in the future. However after having spent the last couple of days reading it seems i underestimated how complex (at least for me) such a thing is,

Reading this thread has been a little painful...For the record, before I sidestepped into IT I was in electronics production and test, beginning with a year of work experience in the GEC calibration labs. That was 30 years ago but I have tried to keep my hand in, so to speak.

PWM is not difficult but you do need a good understanding of Ohm's law and the maths that underlies it. V / I x R, P = I x V

In analogue DC circuits power (P) is controlled continuously by adjusting resistance (R). Voltage is generally assumed to be fixed, so an increase in R reduces current (I) and P also reduces. In the digital domain, R doesn't exist and V can only be on or off. To control P in the digital domain, I is chopped up by rapidly switching V. By adjusting the ratio of Von to Voff within a fixed time-frame (PWM), the average of P is varied over some longer time frame. The rest comes down to design decisions and interfacing electronics.

PWM frequency refers to the length of the time frame, similar to a sample period. PWM duty-cycle refers to the ratio of Von to Voff within the time frame, expressed as a percentage. Only the duty cycle controls power. A 50% duty cycle at 1Hz causes current to be available for 500 milliseconds every second. Increase the frequency to 1KHz and you have 1000x more pulses but the total of Von time over one second is still 500 milliseconds. A 100% duty cycle yields the supply voltage and an effective PWM frequency of 0Hz.

You don't need a special meter to read PWM duty cycle. Any *True RMS* meter with an *AC* range will do but some simple maths is needed to convert the measured voltage to a percentage of the supply voltage resulting in the duty cycle. A % key on the DMM saves doing the maths yourself. The DMM is not measuring the length of the duty cycle but rather measuring the supply voltage and working backwards.

The PWM frequency is a design decision and selected to avoid unwanted artefacts from the D2A conversion. PWM frequencies for dimming LEDs can be as low as 20Hz (20ms) but 120Hz (8ms) is less likely to produce a noticeable flicker. Chassis fan PWM frequencies are typically around 25KHz to avoid creating electrical and audible noise in the sonic spectrum (20Hz to 20Khz).

You can't just poke probes at an open PWM pin and expect to see something useful - You have to read the interface spec and meet the requirements for pull up / pull down and decoupling Etc.

I'm thinking i maybe better off getting a multimeter like the one g8ina and ik9000 kindly linked to

Buying advice in part 2.

[Corky34]

Reading this thread has been a little painful...

You can't just poke probes at an open PWM pin and expect to see something useful - You have to read the interface spec and meet the requirements for pull up / pull down and decoupling Etc.

Sorry, i guess that's what happens when a luddite like me doesn't know what they're talking about.

It's very much appreciated that you've taken the time to write a proper explanation as I'll undoubtedly come back and re-read it when the doing/practice makes something click in my brain, probably doesn't help that maths doesn't come naturally to me and even things like Ohm's law is just a word to me ATM. I may not even be able to workout what i set out to due to ITE not publishing the specs of the controllers so I'm guessing i won't know what the requirements for pull up / pull down and decoupling Etc are, I'm OK with that if I'm honest as it's become about learning more about the things all you guys have talked about.

That's why i prefered the DIY kit thing as it will give me a chance to learn as i go and due to it being partially open source and cheap i can try/confirm things without the worry of turning £50+ into blue smoke.