Wheatstone bridge to measure high resistances?

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SUMMARY

The Wheatstone bridge can measure high resistances, but accuracy diminishes significantly due to the current required for the meter that detects the balance point. The primary challenge arises when measuring resistances above 1 megohm, as the galvanometer's sensitivity (approximately 1 microamp full-scale deflection) limits its effectiveness. To enhance measurement accuracy for resistances of 10^8 ohms or higher, it is essential to replace the galvanometer with a low-offset operational amplifier or utilize a low input bias current inverting transimpedance amplifier. Alternatively, purchasing specialized instruments from Keithley Instruments is recommended for precise measurements.

PREREQUISITES
  • Understanding of Wheatstone bridge principles
  • Knowledge of operational amplifiers and their configurations
  • Familiarity with high-resistance measurement techniques
  • Experience with Keithley Instruments products
NEXT STEPS
  • Research low-offset operational amplifiers for high-resistance applications
  • Study the design and implementation of inverting transimpedance amplifiers
  • Explore Keithley Instruments' product line for high-resistance measurement tools
  • Learn about the limitations and calibration techniques for Wheatstone bridges
USEFUL FOR

Electrical engineers, physicists, and technicians involved in precision resistance measurements and those seeking to enhance their understanding of high-resistance measurement techniques.

tua28494
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Can a wheatstone bridge be used to measure very high resitances with good accuracy? If not what problems interfere?
 
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One problem would be that the current for the meter that detects the balance point has to come through the resistor being measured.

So, you might be trying to detect when the meter is actually reading zero instead of some other very low value of current.

There are ways around this (by adding amplifiers for example) but the basic Wheatstone Bridge would have such difficulties.
 
It has been a long time since I had to use a Wheatstone bridge. I think the highest resistance in it was about 1 megohm. The galvanometer does not carry any current when the bridgre is balanced, but the high-meg resistor R would have to carry ~1 volt/R amps, and the galvanometer might have a full scale deflection of ? 1 microamp ?. So the galvanometer should be replaced with a low-offset op amp. For 10^8 ohms or higher I would either build a low input bias current/low voltage offset inverting transimpedance amplifier, or buy an instrument from Keithley Instruments.

Bob S
 

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