Multimeter, how good does it need to be?

[edeca]

I bought a really cheap (£5/$10) multimeter ages ago. It mainly gets used for testing mains, but I've started using it for electronics. I had to replace the fuse recently (250mA quick blow).

I was playing today with a few Microchip voltage references and a temperature sensor. At first, the meter showed a small negative DC voltage without probes. The output of my 7805 circuit showed around 4.8v and an MCP1541 showed under 4v.

After a while the readings 'corrected', 7805 showed 4.96v and the voltage reference 4.06v. What causes these readings and the correction? The battery should be fairly new and isn't rechargable.

I don't really have much money to spend on a new one, but what should I look for if I buy one? Do I need one, or should a cheap one suffice? I don't mind too much about autoranging, but something accurate enough for this use would be nice!

Interestingly, the one I have appears on the EU "unsafe goods" list (Mastech M-830B). That can't be very good

EUROPA - Consumer Affairs - Unsafe products

 

[Optikon]

I bought a really cheap (£5/$10) multimeter ages ago. It mainly gets used for testing mains, but I've started using it for electronics. I had to replace the fuse recently (250mA quick blow).

I was playing today with a few Microchip voltage references and a temperature sensor. At first, the meter showed a small negative DC voltage without probes. The output of my 7805 circuit showed around 4.8v and an MCP1541 showed under 4v.

After a while the readings 'corrected', 7805 showed 4.96v and the voltage reference 4.06v. What causes these readings and the correction? The battery should be fairly new and isn't rechargable.

I don't really have much money to spend on a new one, but what should I look for if I buy one? Do I need one, or should a cheap one suffice? I don't mind too much about autoranging, but something accurate enough for this use would be nice!

Interestingly, the one I have appears on the EU "unsafe goods" list (Mastech M-830B). That can't be very good

EUROPA - Consumer Affairs - Unsafe products

If all you are concerned about is measuring 7805, then chep meter is fine.

If you need to do more precision work say, < 1% accuracies then I would get a better meter.

 

[Leftyretro]

It really comes down to your needs and applications. There are many inexpensive DVMs available today that can meet many hobbyist needs. There is no need to spend big bucks to get sound performance.

However if one wants the best quality construction, best specifications and is going to use it extensively then brands like Fluke and Agilent (HP) are proven leaders to those that use them professionally. I presently own 2 Fluke model 87s and one model 45 bench meter and can't be more happy with them.

Lefty

 

[crutschow]

After a while the readings 'corrected', 7805 showed 4.96v and the voltage reference 4.06v. What causes these readings and the correction? The battery should be fairly new and isn't rechargable.

The meter variation may be due to bad switch contacts. Older contacts often develop an oxide that can give erratic operation. Application of a "contact cleaner" to the switch contacts, available from most electronic stores, may help.

Interestingly, the one I have appears on the EU "unsafe goods" list (Mastech M-830B). That can't be very good

Sounds like it may be unsafe when measuring high voltages. Probably shouldn't use it above 220V, even if it has ranges higher than that.

 

[HarveyH42]

Perhaps it's 'unsafe', because it doesn't comply with the lead-free society overseas.
I still have and use my first DMM, for under $15, it turned out to be a great buy. The battery last for ever. For most stuff, the number isn't hugely important. Like is an outlet hot (voltage/no voltage), continuity, polarity, stepper motor wires...

 

[edeca]

Perhaps it's 'unsafe', because it doesn't comply with the lead-free society overseas.
I still have and use my first DMM, for under $15, it turned out to be a great buy. The battery last for ever. For most stuff, the number isn't hugely important. Like is an outlet hot (voltage/no voltage), continuity, polarity, stepper motor wires...

Yes, the question "is there mains voltage here" has pretty much been my only usage so far.

However, I was playing with an MCP1541 today which outputs a stable 4.096V for input into an ADC. When the reading was below 4V, I questioned whether it was my interpretation of the datasheet or the meter!

 

[rjvh]

Hi my first meter was a simple cheap meter
then i started to repair stuff and had the chance to buy a fluke (expensive but the best meter i ever had)
i also bought a second one but this was a hoiki (also good but fluke whas better)
then i traveled and moved permently to asia and left everyting that i had in holand by either giving things away or throw it out

i made sombody very happy with the fluke

now i use 4 pairs of cheap made in china multi meters that i buy localy for $2.5 each

and i bought one amp clamp meter for $25

to be onest i only hobby and do some light weight metering stuff but having a set up with 4 meters even when they are not that state of the art is still fine to work with

in this case and i think in 75% of all cases having more than 2 meters instead of 1 hi end meter is more desireable

Robert-Jan

 

[RadioRon]

At your stage in the electronics hobby, I think that the simpest meter is just fine. Better meters add some precision, some additional resolution and considerably more physical ruggedness. Your money may be better spent on some other need besides a meter.

After some thought, I would put a few dollars towards a good soldering iron rather than upgrading a meter.

 

[Sceadwian]

If it's a cheap meter it's probably in the 2-5% accuracy range, at 4.096 volts on the outside that .2 volts. If it's feeding an ADC it's likley a high precision voltage refrence, you could actually use that reading as a refrence to calibrate the meter, as long as the circuit with the voltage refrence is design with the recommended components.

 

[Speakerguy]

I will break from the herd and say buy a tool once. I own a Fluke 177 and I think it's great. The electronics lab I used to work in had a bunch of different brands and we cal'd them against a benchtop 6 1/2 digit meter for ISO certification requirements. The Fluke was the closest, there was an off brand that was close to the Fluke, and then several others that were 'also rans' and not near as good. Fluke 4 Life.

 

[edeca]

Thanks for all the replies, certainly lots to think about. I normally do buy tools once.. but in this case I'd like to get started with the minimum expense.

When I've got my Junebug I'll hook up the voltage reference & temperature sensor to a PIC and see if the A/D comparator in that is better than the meter

 

[blueroomelectronics]

Then you like the CSV 4 channel 10bit A/D recorder project in JPUG issue #2

Junebug CSV 10bit 4 Channel Recorder
AN1,AN2,AN3,AN4
79,95,1016,929
60,51,1016,891
60,85,1016,929
60,49,1016,893
60,84,1016,931
60,47,1016,893
60,84,1016,925
60,47,1016,898
60,84,1016,921

CSV can be imported into Excel or OO Calc

 

[Hero999]

What's the input to your voltage regulator?

Are you sure it isn't dropping out?

I recognise the name of that meter, is it a little grey one and features autoranging? I like it because it fits in my shirt pocket and is very handy for quck tests.