Hello, my name is Ken of Agilent Technologies.
Today I'll show you some techniques
and what you should know when you want to stably measure a low resistance.
This diagram shows a common method to measure low resistance
by using a DC current source and a volt meter.
By limiting the force current, you can avoid damaging the device.
There are a few noise sources which have a large impact this measurement.
First one is power line related.
Power line noise should be cared especially measuring small voltage and current.
As you can see in the left side graph,
just a short period measurement is affected by power line noise.
By integration synchronize to power line period,
you can reject noise effectively.
Second noise and error source is thermal electromotive force, EMF.
EMF causes variation, drift and error of the measurement.
Here, I'll show you two different measurement methods.
One is a single point measurement which only measure here.
This method is easily affected by EMF.
The second is differential measurement.
Applying two diffrent value of current source,
this time positive and then negative current
then calculate resistance value with voltage and current value differences.
By this way, you can reject the error caused by EMF and other offsets.
I'll show you how to connect the instruments to the device.
This is the 10 mohm resistor.
This B2961A which I use as current source is connected to these terminals.
And 34420A, Nono Volt Meter, is connected to these terminals.
I'll show you the difference between single measurement and differential measurement.
To cause EMF effect, I'll hold one terminal for a while.
And after that, repeat measurements.
So let's start the measurement.
This is a similar situation as you set up connections and make measurement right after that.
EMF effect matches especially the case you set small current value
because voltage drop at the device is very small.
This graph shows the result.
Red line is for simple single measurement and blue line is for differential measurement.
Two results are taken at the same time.
From red line, you can see EMF value is changing
and measurement result is drifting and getting closer to the same value as differential measurement.
Blue line shows very stable result.
EMF effect is well eliminated by using differential measurement.
1 PLC integration time is used for this measurement to watch EMF influence clearly.
Let me show the total improvement with PLC integration and differential measurement.
Red line shows the measurement with 0.2 PLC integration and single measurement.
The blue line with 1 PLC and differential measurement.
Differences are obvious.
Red line is affected by power line noise and shows the drift of EMF influence.
Standard deviation of the blue line is about 40 times smaller.
As you can see the couple of techniques to reject noise and errors,
measurement results are much improved.
If you'd like to have more information,
you can visit our web site currently showing below.
Thank you.