How good are cheap multimeters?
Bored Chemist, Mon May 09 2016, 10:08AMSo, it looks like that 10 volt "standard" is about 10 volts, and most of my collection of voltmeters tally.
Re: How good are cheap multimeters?
Bjørn, Mon May 09 2016, 10:31AM
I have some €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.
Bjørn, Mon May 09 2016, 10:31AM
I have some €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.
Re: How good are cheap multimeters?
Mads Barnkob, Mon May 09 2016, 11:02AM
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 :)
Mads Barnkob, Mon May 09 2016, 11:02AM
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 :)
Re: How good are cheap multimeters?
2Spoons, Mon May 09 2016, 10:52PM
I've always found the worst problem with cheap meters is loss of accuracy as the battery drains.
2Spoons, Mon May 09 2016, 10:52PM
I've always found the worst problem with cheap meters is loss of accuracy as the battery drains.
Re: How good are cheap multimeters?
Sulaiman, Tue May 10 2016, 01:20AM
I have killed a couple of £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.
Sulaiman, Tue May 10 2016, 01:20AM
I have killed a couple of £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.
Re: How good are cheap multimeters?
radiotech, Fri May 13 2016, 05:47PM
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.
radiotech, Fri May 13 2016, 05:47PM
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.
Re: How good are cheap multimeters?
Proud Mary, Fri May 13 2016, 06:42PM
I have two identical cheap DVM's that have stout yellow rubber jackets, came from an automotive tools supplier, and cost about £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: √
True RMS: √
Bandwidth (Hz): 100kHz
Diode: √
Transistor: √
Auto Power Off: √
Continuity Buzzer: √
Low Battery Indication: √
Data Hold: √
MAX/MIN: √
RS-232: √
USB Interface: √
LCD Backlight: √
Input Protection: √
Input Impedance for DCV: 600mV Range：Around 3GΩ ,All Other Ranges: Around 10MΩ
Voltage &Current: AC+DC Measurement
Specifications:
DCV: 600mV/6V/60V/600V/1000V ±(0.3%+2)
ACV: 600mV/6V/60V/600V/1000V ±(0.6%+5)
DCA: 600μA/6000μA/60mA/600mA/10A ±(0.5%+3)
ACA: 600μA/6000μA/60mA/600mA/10A ±(1%+5)
Resistance: 600Ω/6kΩ/60kΩ/6MΩ/60MΩ ±(0.5%+2)
Capacitance: 6nF/60nF/600nF/6μF/60μF/600μF/6mF ±(2%+5)
Frequency: 6kHz/60kHz/600kHz/6MHz/60MHz ±(0.1%+3)
Temperature: -40 °C~1000°C/-40°F~1832°F ±(1%+3)/±(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 MΩ, and sometimess less. For high ohmic work, I use a Takeda Riken TR8610 High Megohm Meter, which gives good results up to 10 TΩ providing the sample can withstand 1 kV, and is properly prepared and configured in a shielded box.
Proud Mary, Fri May 13 2016, 06:42PM
I have two identical cheap DVM's that have stout yellow rubber jackets, came from an automotive tools supplier, and cost about £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: √
True RMS: √
Bandwidth (Hz): 100kHz
Diode: √
Transistor: √
Auto Power Off: √
Continuity Buzzer: √
Low Battery Indication: √
Data Hold: √
MAX/MIN: √
RS-232: √
USB Interface: √
LCD Backlight: √
Input Protection: √
Input Impedance for DCV: 600mV Range：Around 3GΩ ,All Other Ranges: Around 10MΩ
Voltage &Current: AC+DC Measurement
Specifications:
DCV: 600mV/6V/60V/600V/1000V ±(0.3%+2)
ACV: 600mV/6V/60V/600V/1000V ±(0.6%+5)
DCA: 600μA/6000μA/60mA/600mA/10A ±(0.5%+3)
ACA: 600μA/6000μA/60mA/600mA/10A ±(1%+5)
Resistance: 600Ω/6kΩ/60kΩ/6MΩ/60MΩ ±(0.5%+2)
Capacitance: 6nF/60nF/600nF/6μF/60μF/600μF/6mF ±(2%+5)
Frequency: 6kHz/60kHz/600kHz/6MHz/60MHz ±(0.1%+3)
Temperature: -40 °C~1000°C/-40°F~1832°F ±(1%+3)/±(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 MΩ, and sometimess less. For high ohmic work, I use a Takeda Riken TR8610 High Megohm Meter, which gives good results up to 10 TΩ providing the sample can withstand 1 kV, and is properly prepared and configured in a shielded box.
Re: How good are cheap multimeters?
Bored Chemist, Fri May 13 2016, 11:27PM
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
Bored Chemist, Fri May 13 2016, 11:27PM
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
Re: How good are cheap multimeters?
Proud Mary, Sat May 14 2016, 10:15AM
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 £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.
Proud Mary, Sat May 14 2016, 10:15AM
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
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 £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.
Re: How good are cheap multimeters?
Wolfram, Sun May 15 2016, 11:23AM
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.
Wolfram, Sun May 15 2016, 11:23AM
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.Re: How good are cheap multimeters?
Proud Mary, Sun May 15 2016, 12:00PM
A very grave lesson indeed.
Similar disasters can happen when TV/CRT servicing HV probes (the 1000:1 divider type) are used to measure sources where significant current can be drawn without pulling down the voltage. It is said that minor surface tracking can very quickly turn into an arc or flash-over under these conditions.
Proud Mary, Sun May 15 2016, 12:00PM
A very grave lesson indeed.
Similar disasters can happen when TV/CRT servicing HV probes (the 1000:1 divider type) are used to measure sources where significant current can be drawn without pulling down the voltage. It is said that minor surface tracking can very quickly turn into an arc or flash-over under these conditions.
Re: How good are cheap multimeters?
Bjørn, Sun May 15 2016, 02:37PM
I have a UNI-T UT61D multimeter that is marked Category IV and it uses the same tiny fuses as the €4 multimeters. It would probably go off like a bomb instead of breaking the current so the rating is not always to be trusted.
ABCs of multimeter safety:
http://support.fluke.com/find-sales/download/asset/1263690_6116_eng_h_w.pdf
Bjørn, Sun May 15 2016, 02:37PM
I have a UNI-T UT61D multimeter that is marked Category IV and it uses the same tiny fuses as the €4 multimeters. It would probably go off like a bomb instead of breaking the current so the rating is not always to be trusted.
ABCs of multimeter safety:
http://support.fluke.com/find-sales/download/asset/1263690_6116_eng_h_w.pdf
Re: How good are cheap multimeters?
radiotech, Mon May 16 2016, 05:08AM
Truly sad commercial accident. Condolences to the Brother's family.
An electromagnetic voltage tester, is called a WIGGY. It is so called because the original was
made by the Wiggington Company. As an electrician for 50 years, that is how I detect the presence
of voltage, up to 600 volts AC or DC.
radiotech, Mon May 16 2016, 05:08AM
Truly sad commercial accident. Condolences to the Brother's family.
An electromagnetic voltage tester, is called a WIGGY. It is so called because the original was
made by the Wiggington Company. As an electrician for 50 years, that is how I detect the presence
of voltage, up to 600 volts AC or DC.
Re: How good are cheap multimeters?
Dr. Slack, Mon May 16 2016, 08:44AM
Yikes. All the stuff in that ABCs of multimeter safety is obvious (sort of), but I hadn't really thought hard about the safety implications of the possible cascade of events before properly. I am guilty of using whatever cheapo meter comes to hand to check the existence of mains voltage, even right at my distribution panel tails.
What I should do is invest immediately in a catIII or preferably catIV meter. What I will probably do is raid my box of HV parts and find some resistors I bought for Marx use, good for 10kV pulse, and build a mains probe that will protect even a catI meter from transients. I don't sell my electrical engineering services, so that's a viable solution. (it turns out that a fairly cheap distributor brand meter I have is alleged to be cat2/1000 cat3/600)
Donning PPE (personal protective equipment) before making a measurement? I am gradually learning to put gloves on before taking a chunk out of my hand with a sharp tool, rather than after, but for making mains measurements? I'll try, honestly, maybe. Fortunately, with an astigmatism, I wear glasses 24/7, so the bare minimum of hardened eyes is met (there has to be an up side to wearing glasses).
Dr. Slack, Mon May 16 2016, 08:44AM
Yikes. All the stuff in that ABCs of multimeter safety is obvious (sort of), but I hadn't really thought hard about the safety implications of the possible cascade of events before properly. I am guilty of using whatever cheapo meter comes to hand to check the existence of mains voltage, even right at my distribution panel tails.
What I should do is invest immediately in a catIII or preferably catIV meter. What I will probably do is raid my box of HV parts and find some resistors I bought for Marx use, good for 10kV pulse, and build a mains probe that will protect even a catI meter from transients. I don't sell my electrical engineering services, so that's a viable solution. (it turns out that a fairly cheap distributor brand meter I have is alleged to be cat2/1000 cat3/600)
Donning PPE (personal protective equipment) before making a measurement? I am gradually learning to put gloves on before taking a chunk out of my hand with a sharp tool, rather than after, but for making mains measurements? I'll try, honestly, maybe. Fortunately, with an astigmatism, I wear glasses 24/7, so the bare minimum of hardened eyes is met (there has to be an up side to wearing glasses).
Re: How good are cheap multimeters?
Proud Mary, Mon May 16 2016, 11:19AM
I received a small but frightening shock from the handle of an HV probe (the 1000:1 type used to service TV CRT EHT supplies) which I had bought on ebay. Inspection of the handle showed that one of four small nylon countersunk screws holding down an inspection plate had been replaced with a metal screw. This metal screw was not in contact with the circuit in the handle - the measuring resistor - and can only have become live as part of a line of least resistance between my hand and the wires within the handle.
The measurand was about 25kV, the maximum safe working voltage of the probe, according to a sticker on the red insulator.
It seems to me that the danger to which I was exposed here was not limited to the small but disagreeable shock from the handle to my hand, but the possibility of a secondary calamity, for example the possibility of my being thrown by muscle contraction onto some other HV equipment etc. by the force of the shock.
Following this event, I obtained from a Polish company a pair of Class 3 insulating gloves certified to 26.5 kV and now wear one of these on the odd occasion when I use an HV probe, with and without metal screws in the handle!
Proud Mary, Mon May 16 2016, 11:19AM
I received a small but frightening shock from the handle of an HV probe (the 1000:1 type used to service TV CRT EHT supplies) which I had bought on ebay. Inspection of the handle showed that one of four small nylon countersunk screws holding down an inspection plate had been replaced with a metal screw. This metal screw was not in contact with the circuit in the handle - the measuring resistor - and can only have become live as part of a line of least resistance between my hand and the wires within the handle.
The measurand was about 25kV, the maximum safe working voltage of the probe, according to a sticker on the red insulator.
It seems to me that the danger to which I was exposed here was not limited to the small but disagreeable shock from the handle to my hand, but the possibility of a secondary calamity, for example the possibility of my being thrown by muscle contraction onto some other HV equipment etc. by the force of the shock.
Following this event, I obtained from a Polish company a pair of Class 3 insulating gloves certified to 26.5 kV and now wear one of these on the odd occasion when I use an HV probe, with and without metal screws in the handle!
Re: How good are cheap multimeters?
rikkitikkitavi, Mon May 16 2016, 12:50PM
For mostly this reason I use my cheap < 10 E meters only at my labbench (isolated 230VAC supply through a not to low impedance variac) and low voltage DC of course.
For household work I use my "real" meters, ie known brand with certified CAT rating.
rikkitikkitavi, Mon May 16 2016, 12:50PM
Wolfram wrote ...
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.
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.For mostly this reason I use my cheap < 10 E meters only at my labbench (isolated 230VAC supply through a not to low impedance variac) and low voltage DC of course.
For household work I use my "real" meters, ie known brand with certified CAT rating.
Re: How good are cheap multimeters?
radiotech, Mon May 16 2016, 04:56PM
In a nutshell. Your little meter is an enclosed air space. An electric arc in that space will heat the air
and everything else too, so quickly that an explosion will take place. Rate of rise of temperature.
Your safety categories are useless once the arc starts. Arcs shoot out highly ionized
gasses, that can short out adjacent conductor pairs of opposite polarity.
You may have noted this phrase on switches and relays. Same polarity only.
The energy that drives the arc, in joules, comes from what you have connected the wires to.
radiotech, Mon May 16 2016, 04:56PM
In a nutshell. Your little meter is an enclosed air space. An electric arc in that space will heat the air
and everything else too, so quickly that an explosion will take place. Rate of rise of temperature.
Your safety categories are useless once the arc starts. Arcs shoot out highly ionized
gasses, that can short out adjacent conductor pairs of opposite polarity.
You may have noted this phrase on switches and relays. Same polarity only.
The energy that drives the arc, in joules, comes from what you have connected the wires to.
Re: How good are cheap multimeters?
hen918, Mon May 16 2016, 05:11PM
I've put enough current through my triggered spark gap to know I don't want that happening in an electrical panel near me. I think an email to my manager is in order: My work multimeter is definitely not up to scratch.
radiotech: I think the idea is to not end up with an arc in the first place. Cat IV probes have built in fuses in the handle that can interrupt more current than the resistance of the test leads allow and multimeters should have large creepage distances, so very high transients don't breakdown into arcs.
Cheap multimeter's traces seem to have a greater current interrupting capability than their fuses in my experience :)
hen918, Mon May 16 2016, 05:11PM
I've put enough current through my triggered spark gap to know I don't want that happening in an electrical panel near me. I think an email to my manager is in order: My work multimeter is definitely not up to scratch.
radiotech: I think the idea is to not end up with an arc in the first place. Cat IV probes have built in fuses in the handle that can interrupt more current than the resistance of the test leads allow and multimeters should have large creepage distances, so very high transients don't breakdown into arcs.
Cheap multimeter's traces seem to have a greater current interrupting capability than their fuses in my experience :)
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