How to measure resistors using PIC controller?

[air]

resistor measurement

10 resistors range from 5k to 120M. How should I measure them using PIC controller. propose some ideas for me please!! thanks.

 

[IanP]

Re: resistor measurement

Using instrumentation amplifiers you will have to build a constant current source in the following ranges:
100 Ω - .99999 kΩ 5 mA
1 kΩ - 9.9999 kΩ 250-500 µA
10 kΩ - 99.999 kΩ 50-80 µA
100 kΩ - 1100 kΩ 5-8 µA
1 MΩ - 9.9999 MΩ 0.5-0,8 µA
10 MΩ - 200 MΩ 50-80 nA
Again using instrumentation amplifier you will buffer test point(s) to directly read voltage. by a microcontroller with ADC (PIC).
For example 120MΩ at 50nA gives you 6V voltage reading..

 

[bzx]

Re: resistor measurement

Using instrumentation amplifiers you will have to build a constant current source in the following ranges:
100 Ω - .99999 kΩ 5 mA
1 kΩ - 9.9999 kΩ 250-500 µA
10 kΩ - 99.999 kΩ 50-80 µA
100 kΩ - 1100 kΩ 5-8 µA
1 MΩ - 9.9999 MΩ 0.5-0,8 µA
10 MΩ - 200 MΩ 50-80 nA
Again using instrumentation amplifier you will buffer test point(s) to directly read voltage. by a microcontroller with ADC (PIC).
For example 120MΩ at 50nA gives you 6V voltage reading..

You need to calibrate each range.

 

[crazy_man]

Re: resistor measurement

use instrumentation amplifiers and calibrate..

 

[H_u_n_t_e_r]

resistor measurement

if your resolution is low then Rx can be use as a feedback resistor in jfet opamp...
Regards.

 

[air]

Re: resistor measurement

Using instrumentation amplifiers you will have to build a constant current source in the following ranges:
100 Ω - .99999 kΩ 5 mA
1 kΩ - 9.9999 kΩ 250-500 µA
10 kΩ - 99.999 kΩ 50-80 µA
100 kΩ - 1100 kΩ 5-8 µA
1 MΩ - 9.9999 MΩ 0.5-0,8 µA
10 MΩ - 200 MΩ 50-80 nA
Again using instrumentation amplifier you will buffer test point(s) to directly read voltage. by a microcontroller with ADC (PIC).
For example 120MΩ at 50nA gives you 6V voltage reading..

Thanks IanP. You mean that using different current source to measure different resistor size right. But in my porject, when the controller is testing thoes 10 resistors one by one (I'm going to use a MUX), both I and the controller do not know which range the resistor will fall in, they are totally random within 5k to 120M range. So I could not choose testing current level beforehand like using multimeter. The testing accuracy requires less than 1%.

 

[IanP]

Re: resistor measurement

That is why you use a microcontroller.
You can implement the same procedure that is used by automatic multimiters: if the reading is below, say, 20% of the range the micro selects next one ..
I don't think without changing currents you will be able to maintain the target accuracy of 1% ..

 

[air]

resistor measurement

I know the principle now. but how to implement the current source and why instrumentation amplifier is needed? Anyone can provide me some reference? Thanks!

 

[air]

resistor measurement

appeal again: anyone can provide me a reference of the constant current circuit?

 

[IanP]

Re: resistor measurement

Examples of constant current sources based on LM334:
https://www.linear.com/pc/downloadDocument.do?navId=H0,C3,P2028,D2715

 

[echo47]

resistor measurement

The HP 3456A is an excellent 6.5 digit meter from about 20 years ago. Here is a scanned PDF of the Theory of Operation chapter from the service manual. Nice simplified schematics, including the ohms current source.
**broken link removed**

That link will disappear in a week or so. Please don't click the "remove it" button. I could upload it here too. About 7.5 MB.

 

[air]

resistor measurement

Thank you very much!