How can I accurately measure high resistances using a lock-in amplifier?

In summary, the speaker has measured some data with diverging resistance using a standard lock-in technique. However, at a certain point, the current starts leaking away due to the input impedance and capacitor. They have also tried measuring with a second lock-in, but are having trouble finding the right approach. They are seeking help with the electrical circuits involved. The person offering help suggests using a lock-in with a current input and being cautious of cable capacitance. They also suggest considering signal guarding or using low frequencies. However, without diagrams, it is difficult to provide further assistance.
  • #1
Erikve
18
0
Dear all,

I measured some very nice data, but it's difficult to analyze, but I try to get out of it what I can. I have diverging resistance and did measure with standard lock-teqnique: apply 0.45V over preresistor and send current over sample and measure the two-probe resistance over the same contacts as where I send the current.
At the moment that the sample reaches the border of 10MOhm we get of course problems since current starts leaking away via the 100MOhm input-impedance of the lock-in and the capacitor of 25pF. I measured the current with a second lock-in. With this data I should be able to extract still quite the resistances up to 1 GOhm, but somehow I cannot find the right way how to deal with this.

Somebody who can help me out of the spaghetti of electrical circuits?
Thanks you.
 
Engineering news on Phys.org
  • #2
What Type of Lockin do you use? What frequencies? Some lockins have a current input (Those from "Signal Recovery" for example) With a cable that is patched the right way, you can measure resistances without a pre resistor. You have to be careful, because the cable capacitance will produce quite a low pass. Maybe you should think about signal guarding too, or use low frequencies. Are you sure that the second lockin was locked to the first lockins signal? It's hard to help you with spaghetti without any diagrams.
 

1. What is a lock-in amplifier?

A lock-in amplifier is a specialized electronic instrument used to measure very small signals in the presence of high levels of noise. It works by multiplying the measured signal with a reference signal, which allows it to extract the desired signal from the noise.

2. How does a lock-in amplifier work?

A lock-in amplifier works by receiving a signal from the device being measured and multiplying it with a reference signal that is synchronized with the signal. This process is repeated multiple times and the results are averaged, resulting in a highly accurate measurement of the desired signal.

3. What types of signals can a lock-in amplifier measure?

A lock-in amplifier can measure AC signals with frequencies ranging from a few Hertz to several GHz. It is commonly used in scientific experiments to measure signals from sources such as lasers, LEDs, and photodiodes.

4. What are the advantages of using a lock-in amplifier?

The main advantage of using a lock-in amplifier is its ability to extract small signals from high levels of noise. It also provides a highly accurate measurement of the desired signal, as well as the ability to measure signals with very low frequencies.

5. In what types of experiments is a lock-in amplifier commonly used?

A lock-in amplifier is commonly used in experiments that involve measuring small signals in the presence of noise, such as in spectroscopy, microscopy, and other types of optical and electronic measurements. It is also used in studies of electrical and magnetic properties of materials.

Similar threads

  • Electrical Engineering
Replies
3
Views
2K
  • Other Physics Topics
Replies
3
Views
961
  • Atomic and Condensed Matter
Replies
6
Views
2K
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
3K
Replies
8
Views
2K
Back
Top