You pays for what you gets.
A reasonable DMM will give yo +/- 1% plus +/- 1 digit.
The highest accuracy is usually on the DC voltage range. You can use this to your advantage by simply using a potential divider to measure your resistors. Even better a Wheatstone Bridge.
A reasonable DMM will give yo +/- 1% plus +/- 1 digit.
The highest accuracy is usually on the DC voltage range. You can use this to your advantage by simply using a potential divider to measure your resistors. Even better a Wheatstone Bridge.
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I'll assume that your DMM is 3 1/2 digit model, most of them are.
Therefore if you had a 100.00% accurate 0.47 Ohm resistor your meter might display:
0.47 +/- 1% = 0.478 to 0.462 Ohms
This also depends on the firmware in the DMM, does it Round-Up or Round-Down, will it remove the leading ZERO.
0.47 + 1% = 0.475
Depending on whether your meters rounds this up or down could be
0.47 or 0.48 the the last digit could be up to 3 counts "OFF"
Which would give you 0.44 to 0.51
Similarly
0.47 - 1% = 0.465
Which would give you 0.43 to 0.50
So a perfectly good 1% -.47R resistor on your meter could read between
0.43 and 0.51 Ohms.
If you need better accuracy, just buy better resistors. The DMM will just serve to tell you that the resistors hasn't failed.
Then, if an instrument has 3 decimal display, am I correct under the same accuracy, that the 0.470 ohm will have a reading between
0.470 + 1% = 0.4747 = 0.475 + 3 = 0.478
or
0.470 - 1% = 0.4653 = 0.465 -3 = 0.462
Therefore an instrument which has 3 decimal display will have a better accuracy than that has only 2 decimal display. Am I right?
0.470 + 1% = 0.4747 = 0.475 + 3 = 0.478
or
0.470 - 1% = 0.4653 = 0.465 -3 = 0.462
Therefore an instrument which has 3 decimal display will have a better accuracy than that has only 2 decimal display. Am I right?
Hi,
FWIW you can't use the stated accuracy when measuring low value resistors.
The contact resistance of the probes is significant. For accuracy you would
need to treat it as a 4 terminal device, i.e. feed the resistor with a known
precision current and then measure the voltage across the resistor.
Only then will the meters specified accuracy be applicable.
rgds, sreten.
FWIW you can't use the stated accuracy when measuring low value resistors.
The contact resistance of the probes is significant. For accuracy you would
need to treat it as a 4 terminal device, i.e. feed the resistor with a known
precision current and then measure the voltage across the resistor.
Only then will the meters specified accuracy be applicable.
rgds, sreten.
Yes, the instrument I am considering is using DC with temperature control. It is made in China and being sold in Taobao.com
»Ê¹Ú ʵÌåµêÏúÊÛ³£ÖÝͬ»ÝTH2512BÖ±Á÷µÍµç×è²âÊÔÒÇ-ÌÔ±¦Íø
Unfortunately, the webpage is only in Chinese.
»Ê¹Ú ʵÌåµêÏúÊÛ³£ÖÝͬ»ÝTH2512BÖ±Á÷µÍµç×è²âÊÔÒÇ-ÌÔ±¦Íø
Unfortunately, the webpage is only in Chinese.
That should be tonghui TH2512B meter,
here the specs:
DC Low-Ohm Tester
it says 0.1%+2 counts, has 20mOhm to 20kOhm ranges,
4 and half digit, I dont't have tonghui equipment but I have
read that theirs LCR meters are not bad.
For your example 0,47 ohm you have 2Ohm range
with a full reading of 0,4700 ohm, more than enough resolution.
Fabio.
Thank you for your detail explanation.
I need a low ohm meter because I need to wire wound a coil with 0.47 ohm DC resistance therefore I started to look at low ohm meters. The first one I encountered was one stating + - 1%+3 that costs about US$65. Without knowledge, I thought it cannot read accurate for the captioned 0.47 ohms therefore I started looking for Tonghui.
In my application, I think the cheaper one will work.
I need a low ohm meter because I need to wire wound a coil with 0.47 ohm DC resistance therefore I started to look at low ohm meters. The first one I encountered was one stating + - 1%+3 that costs about US$65. Without knowledge, I thought it cannot read accurate for the captioned 0.47 ohms therefore I started looking for Tonghui.
In my application, I think the cheaper one will work.
Yes, I have a good multi-tester, a China made constant current supply and some 100 ohms 0.1% resistors made by Texascomponent but they are only 0.75W. I think I can parallel 4 of them to sustain the current up to 300mA. However, the 0.47ohm wire wound resistor is make for a filament supply that is drawing 2.5A, would the test current at 300mA too low?
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