Looking for 1 Mega ohm range mesurment circuit

[spl]

Hello Friends,
  I looking for circuit for measurment resistor range 220K - 1 M ohm
by using source voltage about 1 V (the system must be 4 wire methods)
Thank you very much..

[FriskyFerret]

Too little info, like usual. Why do you need 4-wire? This method is often used for high precision or low-ohm measurements.

This smells like a school assignment.

[spl]

Yeap..
   Actually , This 's  will be apply for discharge resistance measurement system, Normally the DUT is parallel
connected  will capacitor range about 1 - 10 uF (400V rated). The circuit would able to pre-charge with some voltage source before can read the DC resistance. The Accuracy must be  with in 5 % at 1 Mohm.
If someone have any idea for this solution please give me your comment.
Thank you very much.


Posted on: June 07, 2008, 04:25:28 04:25 - Automerged
Now , This in instrument has designed by using micro controller for control and measurement also
interface to the test system process controller. The last point  is the instrument circuit part only.

[DTiziano]

At that specifications the current in the DUT will be 1 uA +- 50 nA.
The capacitor leakage should be very low at that voltage so no problem.

A solution can be implemented by a Wheaston bridge supplied at 2 V
as well as driving the reference of the ADC converter.
Three legs with 1M resistance and the fourt with DUT.
If DUT is on the ground side the Rx vaule (Mohm) is = (delta V + 1) / (1- delta V).
To get delta V (positive side on the DUT) you need an OP with low input current (<< 50 nA)
and low offset.

[lillbear]

I need to measure 1-5G Ohm resistors. Is Wheaston bridge suitable for this?

yours

[zuisti]

I need to measure 1-5G Ohm resistors. Is Wheaston bridge suitable for this?

No, according to my opinion it doesn't suitable in this case. Simply use a current measure circuit instead, using a relative high measuring voltage, for example 100 V if possible, so you can measure 100 V/5 GOhm = 10**2/5*10**9 = 2*10**-8 = 20 nA for 5G (and 100 nA = 0.1 uA for 1G) !!!  I think this is possible.

[DTiziano]

Take care that at such high values (voltage and resistance) and low currents, leakage can be a big problem.
Every thing must be clean and well isolated. Not an easy task.
 

[anemon06]

If you serve, this circuits measure until 1 Mohm