The significant factor is the current through it, the voltage applied is proportional to the resistance of the meters, the one with the lowest current ( not necessarily the one with the lowest voltage)( probably( maybe you need a threshold voltage)) is the best for the job.
The Wheatstone bridge has 0 current and 0 voltage when balanced, thus the resistance is known.
Sensor testing
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
I have boloxed it up with the Wheatstone bridge. Just looked up Wheatstone bridge. There is another resistor bridge where no current flows and voltage across the resistor is 0...When the bridge is balanced.
I will have to think about it, it can be done.
I will have to think about it, it can be done.
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
OK ... Best I can do for now, its late I have a low bat.
The problem is current, obviously due to applied voltage but also meter resistance.
The primary factors of the resistance in question are, field intensity and direction on current and rate of change of current, in the sensor.
Resistance can only be measured by passing a current through the resistor. When field intensity is constant and current is constant, resistance is constant...
A Wheatstone bridge and fine ammeter, being the most accurate way of doing it.
Voltage as low as poss, the meter must be micro volts or so, it to s difficult to calibrate the meter because the meter reading its output will effect it, just as it effects the sensor though perhaps for different reasons. ( another story).
The Wheatstone bridge at a range of currents is the most accurate way to do it because current is known, with the meter it is not.
I made a bolox up of the 0V, 0A bit, it just struck me. I am right about the current, I think impedance is insignificant except, for a milli sec or so, and unless you can measure resistance without a current or invent a perpetual motion machine, the Wheatstone bridge is the best solution.
The problem is current, obviously due to applied voltage but also meter resistance.
The primary factors of the resistance in question are, field intensity and direction on current and rate of change of current, in the sensor.
Resistance can only be measured by passing a current through the resistor. When field intensity is constant and current is constant, resistance is constant...
A Wheatstone bridge and fine ammeter, being the most accurate way of doing it.
Voltage as low as poss, the meter must be micro volts or so, it to s difficult to calibrate the meter because the meter reading its output will effect it, just as it effects the sensor though perhaps for different reasons. ( another story).
The Wheatstone bridge at a range of currents is the most accurate way to do it because current is known, with the meter it is not.
I made a bolox up of the 0V, 0A bit, it just struck me. I am right about the current, I think impedance is insignificant except, for a milli sec or so, and unless you can measure resistance without a current or invent a perpetual motion machine, the Wheatstone bridge is the best solution.
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
The closest to 0V is AC across the bridge, the net result =0 V low bat.
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
If you put a magnet on the sensor in the direction of the sensor, the significance of current will be less and the meters will all read the same.
Tar&stuff.
Tar&stuff.
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
A high frequencyAC Wheatstone bridge with rectified galvanometer would perhaps be the most effective way to measure resistance, in the absence of a magnetic field.
As I said in the last post, put a magnet on the sensor, as field intensity exerts greater force than the uuA ( what ever it is) current, current is negligible... The meters all read the same.
That's about it as far as I am concerned, sorry for posting pages and pages on your thread, I hope the last few posts help
You can start the thread again and I will mind my own business if you want, very interesting problem, I could not sleep till I cracked it.
Tar&stuff.
As I said in the last post, put a magnet on the sensor, as field intensity exerts greater force than the uuA ( what ever it is) current, current is negligible... The meters all read the same.
That's about it as far as I am concerned, sorry for posting pages and pages on your thread, I hope the last few posts help
You can start the thread again and I will mind my own business if you want, very interesting problem, I could not sleep till I cracked it.
Tar&stuff.
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piratepaul
- Posts: 432
- Joined: Mon May 20, 2013 2:45 pm
Re: Sensor testing
Can't help myself... If you put the magnet near the sensor so the direction of field is in the direction of the sensor, take a reading with both meters, move the magnet closer and take readings ...etc put the magnet as close as it needs to be to bring both meters into tolerance.
That's it from me.
Tar&stuff.
That's it from me.
Tar&stuff.
Re: Sensor testing
Most multimeters have an internal cell or battery which is used on the ohms ranges. I can well appreciate that trying to measure a resistance in a circuit which contains semiconductors (transistors, ICs, etc.) would give rise to different readings because of the applied voltage from the meter. Why not try connecting another meter on a volts range straight to the leads of the ohmmeter (i.e. not connected to anything else) and see if there is any difference between the meters you have available?