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How good are cheap multimeters?

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LAN_403

Bored Chemist

Mon May 09 2016, 10:08AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

So, it looks like that 10 volt "standard" is about 10 volts, and most of my collection of voltmeters tally.

Bjørn

Mon May 09 2016, 10:31AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I have some â‚¬4 multimeters and they are accurate enough for all common use and cheap enough that you don't have to be very careful with them. No reading is worse than a medium accuracy reading so an expensive multimeter that you don't dare float at 10 kV is a bit of a waste.

Some multimeters, possible the yellow one on the far right use chip on board packaging that is not shielded well enough from light so infrared light can penetrate the case and cause a false reading. Here is one with the back off and a 50 W halogen lamp pointed at the back showing 57 V with no test leads. In sunlight it can be a few volts off on some settings with the case on.

Mads Barnkob

Mon May 09 2016, 11:02AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Could you please update the main post with brand, model numbers and their readings?

Just so that there is actually some solid information supplied and that will for the future show up on search engines :)

2Spoons

Mon May 09 2016, 10:52PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

I've always found the worst problem with cheap meters is loss of accuracy as the battery drains.

Sulaiman

Tue May 10 2016, 01:20AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I have killed a couple of Â£2.99 dmm, they died bravely.
They were within their specifications on all ranges (vs. calibrated Fluke 187)
but just because there is a 2000 Volt range
do not assume that it will not suddenly discharge a capacitor bank above about 1.2 kV ...
even 415 V 3-phase is a serious risk.
Other than that, excellent value.

radiotech

Fri May 13 2016, 05:47PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The current crop of 4000 count meters has improved radically lately. I have two sets of 12
used in my classes. The new set I bought uses 2 x AAA instead of the expensive 9 volt one.

The older meter has about 11 pots inside to calibrate everything.

The new meter has no pots.

An associate of mine tells me the meter folk have developed a generic chip
that can be programmed, and calibrated , to fit whatever the market wants it to do.

The meter crowd thinks they can hack it too. They think that is because calibration has to done
after assembly of the meter.

My meters sell for $70. but regularly are discounted to $30.

They are safety approved to 750 VRMS and 1000 VDC.

However the AC voltage and current range accuracy is rated between 40 and 400 Hz.

The frequency counter goes to 400 kHz.

The mechanism of the switch is simple, two ball bearing in a detent wheel.

I already destroyed a new meter when a tiny contact flew out on disassembly
and by the time i found it, I had stepped on it.

I also have a set of Radio Shack DVMs, known to student proof. They still
work fine after 30 years. I use them because they have a - 27 to +54 dBm range.
to Those cost $130 in their day.

1463161644 2463 FT176725 Mastercraft 052 0052 2 From Canadian Tire

Proud Mary

Fri May 13 2016, 06:42PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have two identical cheap DVM's that have stout yellow rubber jackets, came from an automotive tools supplier, and cost about Â£10 (about EUR 13) each. They have no maker's name or number on the case. I find them very suitable for most ordinary tasks when no special accuracy is required.

I also have a Uni-T UT803 USB bench multimeter which can, for example only, take and store n readings at any specified interval. I do not let high voltages anywhere near this meter.

Its Features are:
Display Count: 6000
Auto Range: âˆš
True RMS: âˆš
Bandwidth (Hz): 100kHz
Diode: âˆš
Transistor: âˆš
Auto Power Off: âˆš
Continuity Buzzer: âˆš
Low Battery Indication: âˆš
Data Hold: âˆš
MAX/MIN: âˆš
RS-232: âˆš
USB Interface: âˆš
LCD Backlight: âˆš
Input Protection: âˆš
Input Impedance for DCV: 600mV Rangeï¼šAround 3GÎ© ,All Other Ranges: Around 10MÎ©
Voltage &Current: AC+DC Measurement

Specifications:
DCV: 600mV/6V/60V/600V/1000V Â±(0.3%+2)
ACV: 600mV/6V/60V/600V/1000V Â±(0.6%+5)
DCA: 600Î¼A/6000Î¼A/60mA/600mA/10A Â±(0.5%+3)
ACA: 600Î¼A/6000Î¼A/60mA/600mA/10A Â±(1%+5)
Resistance: 600Î©/6kÎ©/60kÎ©/6MÎ©/60MÎ© Â±(0.5%+2)
Capacitance: 6nF/60nF/600nF/6Î¼F/60Î¼F/600Î¼F/6mF Â±(2%+5)
Frequency: 6kHz/60kHz/600kHz/6MHz/60MHz Â±(0.1%+3)
Temperature: -40 Â°C~1000Â°C/-40Â°F~1832Â°F Â±(1%+3)/Â±(1.5%+5)

I have found the worst failing with general purpose DVMs to be in high resistance measurements, where really large errors can occur once you pass 100 MÎ©, and sometimess less. For high ohmic work, I use a Takeda Riken TR8610 High Megohm Meter, which gives good results up to 10 TÎ© providing the sample can withstand 1 kV, and is properly prepared and configured in a shielded box.

Bored Chemist

Fri May 13 2016, 11:27PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

High resistance measurement is an art form in its own right.
The equipment isn't the real challenge.

The ten quid no-name yellow DVM , set on its 200mV range is a passable low current meter.
Typically 1Mohm input resistance, so, to drop 200 mV would take 200 nA and it registers down to 0.1 nA.
With a stack of 9 volt batteries to give you "99" volts you are up into the T ohm territory (OK.-with shoddy precision).You can do better still with a 1KV PSU.
The difficult bit is working out where all the stray currents are going, and how to put guard rings in the right places.
Of course, you need to remember to subtract the 1 Mohm resistance of the meter

Proud Mary

Sat May 14 2016, 10:15AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Bored Chemist wrote ...

High resistance measurement is an art form in its own right.
The equipment isn't the real challenge.

The ten quid no-name yellow DVM , set on its 200mV range is a passable low current meter.
Typically 1Mohm input resistance, so, to drop 200 mV would take 200 nA and it registers down to 0.1 nA.
With a stack of 9 volt batteries to give you "99" volts you are up into the T ohm territory (OK.-with shoddy precision).You can do better still with a 1KV PSU.
The difficult bit is working out where all the stray currents are going, and how to put guard rings in the right places.
Of course, you need to remember to subtract the 1 Mohm resistance of the meter

I was lucky to get my High Megohm Meter very cheaply, and with its guarded inputs and switchable HV supply it is certainly much better than anything I could have built myself without making a crusade of it.

Back to the original topic, there looks to be a consensus that very useful and reliable multimeters can now be had for so little that the newcomer shouldn't expect to pay much more than about Â£10, EUR 13, US$ 15, to get a serviceable instrument that will last a long time if kept away from the rogue transients that have wrecked so many.

Wolfram

Sun May 15 2016, 11:23AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

The only major caveat with cheap meters is that they often have very poor input protection, replacing expensive HRC fuses with cheap glass fuses. This can be very dangerous in situations where high fault current is available. This is mainly a concern when measuring supply-side mains wiring and capacitor banks. See this link

for an account of the failure of a cheap multimeter leading to two deaths.

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