The answer is from google but I don't get it. Can someone explain in more simple way?
Electronic – Why can’t a Wheatstone bridge measure resistance of very high value
bridgeresistancewheatstone-bridge
Related Solutions
This should get you close. By my calcs, in your range the thermistor will be going from about 1 ohm to about 6 ohms. With a 1K resistor to hold currents down to milliamps, you need a gain of about 35 to keep your max voltage at 1V. This circuit has a gain of 34 using standard 5% resistor values. You might need to change to a rail-to-rail op amp if you're going to power it with a one-sided supply.
Your bridge connection is most likely rotated by 90 degrees. No bridge would ever have this much offset. If you are sure it is not damaged, first disconnect any circuitry on the output pins and measure again. Then, check the pinouts and make sure they are properly connected. Best bet is to try rotating the strain gauge; that is, apply power to SP and SN and measure EP and EN. Many bridges are only symmetrical in one orientation, and the measure taps are not exactly halfway between power and ground.
Best Answer
You are mixing things up, the text talks about a galvanometer which is an electomechanical device which draws its power from the circuit in which it is used.
When the currents become too small (less than a few micro Ampere) a galvanometer cannot be used anymore as you will not see the needle move anymore.
A Wheatstone Bridge:
Is a circuit which can be used to determine the ratio of values of components. As such it is suitable also for high value resistors. What is required though is a sensitive volt/current meter in the middle.
A galvanometer is not that sensitive so a Wheatstone Bridge using a galvanometer is limited to resistor values up to around maybe 1 Mega ohm.
Replace the galvanometer with a more sensitive (electronic) meter (which could still have a galvanometer for readout) and you can use the Wheatstone Bridge also with high resistor values.
So the limitation is not due to the Wheatstone bridge but due to the galvanometer.