I cannot figure out how to get an accurate measurement of a .47 3 watt resistor and a .56 3 watt resistor.
.47 3watt; cpf3r47000jnb14 and erx-3sjr47v
.56 3watt; rro3jr56tb
The .47 measure .6 sometimes .5. The .56 measure .7 sometimes .6. Is this as close as I can get with this type of mulimeter?
.47 3watt; cpf3r47000jnb14 and erx-3sjr47v
.56 3watt; rro3jr56tb
The .47 measure .6 sometimes .5. The .56 measure .7 sometimes .6. Is this as close as I can get with this type of mulimeter?
Erratic lead contact. The leads also have resistance themselves. And the last digit (0.1 ohm) limits the resolution.
For best results, forget the leads, and instead solder the ends of the resistor to banana plugs,
and plug them directly into the meter socket. But the accuracy is still +/- 0.1 ohm at best.
Any better accuracy requires more specialized test equipment.
You could solder ten of the same value resistors in series and connect them to a 10VDC power supply
(about 2W dissipation each), and measure the DC voltage on each (about 1VDC).
The resistors with similar voltages will be similar resistances, since the current is the same in each.
For best results, forget the leads, and instead solder the ends of the resistor to banana plugs,
and plug them directly into the meter socket. But the accuracy is still +/- 0.1 ohm at best.
Any better accuracy requires more specialized test equipment.
You could solder ten of the same value resistors in series and connect them to a 10VDC power supply
(about 2W dissipation each), and measure the DC voltage on each (about 1VDC).
The resistors with similar voltages will be similar resistances, since the current is the same in each.
Range/resolution | 600.0 Ω / 0.1 Ω resolution 6.000 kΩ / 0.001 kΩ 60.00 kΩ / 0.01 kΩ 600.0 kΩ / 0.1 kΩ 6.000 MΩ / 0.001 MΩ |
| Accuracy | 0.9% + 1 |
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Measuring low resistance resistors (say <10 Ω) can be a challenge with hand-held multimeters. The contact resistance between the probes and the resistor leads will vary depending on how you hold the probes to the leads, contact pressure, etc. Then add that the meter isn't terribly accurate at low resistances either. Below is from Fluke's website:
If I interpret this correctly, you have 0.1 Ω resolution at the lowest range, 0.9% + 1 digit accuracy. So a 1.00 Ω resistor may read 0.8-1.1 Ω on the display.
If you want greater precision measurements of low-ohm resistors you should look into setting up a 4-wire measurement.
Tom
If I interpret this correctly, you have 0.1 Ω resolution at the lowest range, 0.9% + 1 digit accuracy. So a 1.00 Ω resistor may read 0.8-1.1 Ω on the display.
If you want greater precision measurements of low-ohm resistors you should look into setting up a 4-wire measurement.
Tom
Thank you everyone. It really is a pleasure not being afraid to be judged harshly for simple questions. The people on this site never let me down.
Precision measurements are very problematic. Anyone who thinks this stuff is simple needs to educate themselves.
It's easier to match parts than to get absolute measurements for one part, although the parts and test equipment must
have sufficient stability to make the matching meaningful.
https://www.nist.gov/metrology
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The best way to precisely measure resistors is the Wheatstone bridge as mentioned by Tom.
Fascinating stuff..
https://en.wikipedia.org/wiki/Wheatstone_bridge
Hugo
Fascinating stuff..
https://en.wikipedia.org/wiki/Wheatstone_bridge
Hugo
The Wheatstone bridge is one approach. I was referring to 4-wire sensing (aka Kelvin sensing) though: https://en.wikipedia.org/wiki/Four-terminal_sensing Many bench top DMMs (such as the HP 34401A) offer 4-wire sensing.
One way to measure a low resistance is to force a known current through the resistor and measure the voltage developed across the resistor.
The Wheatstone bridge would be a good option if you're trying to match the resistors but don't care so much about their absolute value.
Tom
One way to measure a low resistance is to force a known current through the resistor and measure the voltage developed across the resistor.
The Wheatstone bridge would be a good option if you're trying to match the resistors but don't care so much about their absolute value.
Tom
Thanks Tom, I'll have a closer look at all the variations. I wasn't aware of their existance and love the look of these old instruments.
Hugo
Hugo
I'd say get some good leads that can also take croc clips on them. Possibly a kit like this
https://uk.rs-online.com/web/p/multimeter-leads/1253735?gb=s
There are also kits with the smaller sized clip and different probe ends. Main problem is these kits can cost the price of some multimeters. Fluke uusually supply leads that wont have this sort of problem over years of use. It's no good pressing the normal probes up against restistors unless the leads are extremely fresh. Croc clips can be rocked about a bit to fix that - if it's a problem.
https://uk.rs-online.com/web/p/multimeter-leads/1253735?gb=s
There are also kits with the smaller sized clip and different probe ends. Main problem is these kits can cost the price of some multimeters. Fluke uusually supply leads that wont have this sort of problem over years of use. It's no good pressing the normal probes up against restistors unless the leads are extremely fresh. Croc clips can be rocked about a bit to fix that - if it's a problem.
You cannot measure low value resistors directly with a multimeter unless you have a 4 wire device, otherwise resistance of the test lead will degrade the precision so much you will not have the value.
So to get a fair measure you will need a DC low voltage power supply or a battery let say around 12 volts
A known value resistor maybe around 100 ohms
Then connect the 2 resistors in serie and connect the circuit to the power supply
Now you will have to measure the voltage drop across each resistors BUT you must make shure that your probes are as close as possible to the resistor body.
Since voltage drop across each resistor is proportional to the voltage drop you can calculte the value of the unknown resistor.
So to get a fair measure you will need a DC low voltage power supply or a battery let say around 12 volts
A known value resistor maybe around 100 ohms
Then connect the 2 resistors in serie and connect the circuit to the power supply
Now you will have to measure the voltage drop across each resistors BUT you must make shure that your probes are as close as possible to the resistor body.
Since voltage drop across each resistor is proportional to the voltage drop you can calculte the value of the unknown resistor.
If you have two DMM's, you can make a DIY 4-wire sensing (aka Kelvin sensing) meter.
And some current source. Use one DMM to measure current thru the resistor and the other DMM to measure voltage drop.
far down the page see "Photographs Relating to Four Terminal Resistors."
http://www.beta-a2.com/EE-photos.html
And some current source. Use one DMM to measure current thru the resistor and the other DMM to measure voltage drop.
far down the page see "Photographs Relating to Four Terminal Resistors."
http://www.beta-a2.com/EE-photos.html
A bench power supply with current metering plus one multimeter will do 4-terminal measurement very easily. This can be improved by adding another (good) multimeter to measure the current more accurately.
Simply set up the current circuit, then touch the voltage multimeter probes to the ends of the resistor leads, note the current and voltage readings, R = V/I.
I've measured the resistance of large busbars this way even - if your bench supply can push 3A and your multimeter has a 200uV scale, you can measure fractions of a milliohm this way. Certainly with more accuracy than a standard multimeter can measure below 10 ohms.
Simply set up the current circuit, then touch the voltage multimeter probes to the ends of the resistor leads, note the current and voltage readings, R = V/I.
I've measured the resistance of large busbars this way even - if your bench supply can push 3A and your multimeter has a 200uV scale, you can measure fractions of a milliohm this way. Certainly with more accuracy than a standard multimeter can measure below 10 ohms.
What I have done is put the low value resistor in series with a high value resistor and apply a voltage. The resistance of the high value resistor can be measured beforehand and using the voltage drop across it, the current can be calculated. The voltage drop across the low value resistor is also measured and used in conjunction with the calculated current to determine the resistance.
The specifications list the limit of .1 ohms on the 600 ohm range. To measure low value resistors manually set the range to 600 ohms. Then using clip leads connect both leads to just one side of the resistor. This should give you a reading of less than .3 ohms. Now move one lead to the other side of the resistor. This should read a bit higher. Now subtract the first reading from the second, that should be the resistor value as you have essentially subtracted the lead set resistance.