Very Low Resistance Measurement (Less than 1 Ohm)

[glenjoy]

why less than 1 ohm

I am designing a system that will measure a very low resitance.

The system will measure resistance bank but the resitance to be measured are not connected to each other so to get one resistance, I will be using a multiplexer, analog multiplexer to be exact.

Now, I need pointers on the design, to be exact, the design will be used to measure the kelvin contactors of a semiconductor testing equipment.

I also need a constant current source that will not change its output current when I sink a current to a load.

Say the constant current source sinks a 100mA at any load.

 

[nicleo]

less than 1 ohm resistor

Usually we use 4-wire method to measure low resistance. You may also consider using 6-wire approach like here: **broken link removed**

 

[ezpcb]

measuring very low resistance

Wish this circuit helpful

mike


-------------------------------------------------
www.ezpcb.com
$50 high quality PCB prototyping

 

[glenjoy]

stabilized power supply with current control

As much the design is concerned, I want to measure a less than 1 Ohm resistance and wanted to eliminate the presence of Analog Switch resistance.

No relays must be used also.

 

[tobb]

very low resistance measurements

for constance current source you could try **broken link removed** looking for 0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A
it could give you a constance current range up to 3 A
I used it with my Magnetic Field Tester and it works well.. I have change control from Knob vr to Digital by using ADUC0832 to control current and read back feedback with it own 12bit A2D and DAC
you could possible to read voltage across wire with less than 1 Ohm.. But it will be very hot.

 

[sinatra]

measure less than 1 ohm

As I can see your system alows a reasonably high current to be used, as you said 100mA is feasable.....
You could also consider discharging a large capacitor through this low resistance and measure the discharge time instead of measuring any voltage.
You can charge a large capacitor slowly through a low current power supply.
When the change is finished you can discharge the capacitor through the resistor to be measured using a mos switch.
The timing signal can be obtained just by conecting a smith trigger to the capacitor lead....etc..

About the DC method you proposed:
Since reasonably high currents are alowed it shouldn't be difficult to measure a voltage drop in your resistor, 100mA makes a voltage drop of 100mV in a 1 ohm resistor. It should be very easy to measure it with an operational amplifier with low off set like op177.
Lower currents would also be enough. With the high precision opamps we have today it will not be impossible to measure voltages even lower, as 1mV for example....

hope it helps.
S.

 

[glenjoy]

how to get a resistance less than one ohm

for constance current source you could try h**p://electronics.cjb.net/ looking for 0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A
it could give you a constance current range up to 3 A
I used it with my Magnetic Field Tester and it works well.. I have change control from Knob vr to Digital by using ADUC0832 to control current and read back feedback with it own 12bit A2D and DAC
you could possible to read voltage across wire with less than 1 Ohm.. But it will be very hot.

I am not talking about powetr supply here, are you newbie in design? It is quite obvoius that you cannot understand my post.

So please next time, ask first if question is not clear so you will not post crazy answers.

 

[IanP]

resistance less than 1 ohm

Here is a concept of sinking constant current source.
You will not need two branches - one is enough .. Istead of 324 opamp you can use LM358 or for single voly operation CA3130 ..

 

[mark_nctu]

electronics.cjb.net

You can use four point probing method to reduce measuring effor and
don't need 100mA curent source.

 

[glenjoy]

less than 1 ohm

A current source is needed so that the rsistance will be read by an ADC.

 

[the tran]

how to measure resistance lower than 1 ohm

hello glenjoy
hope this link helps
www.optics.arizona.edu/Palmer/ OPTI380B/PDFdocs/5950-3000.pdf

 

[Epegic]

low resistance measurement

There is a MCU controlled lock-in amplify design on http://projects.cappels.org/ to measure low resistance.

 

[glenjoy]

very low resistances are measured using

Any designs for a constant current injectors? Thanks.

 

[carrier]

is less than 1 ohm good?

for better drive circuit in current source use this circuit.
this circuit cancel the effect of base current of bjt.

 

[Evo]

0,1ohm hight precision resistance

hey,

1ohm low impedance measurement is critical, no doubt. i think you need to check how Agilent design their impedance measurement equipment. they are the best equipment vendor of the low impedance measurement. i attended the class, but couldn't recall how the whole idea was.

but for 10mohm measurement, the DUT has to be gold platted.

 

[H_u_n_t_e_r]

resistance less than one ohm

you can use ref200 from texas with an low Vofset and low Vnoise instrumentation opamp from analog device..

 

[Moss]

There is a way to measure low impedances with AC current source as shown on AD appnote 306.Advantage is that such system can have resolution below 0.1mOhm despite of very small injecting current (1mA).