[HELP]-Concept of Ohm Meter

[mrfunkyjay]

Hi all, to begin with, my name is Kelvin. I am now doing research for my final study project, thesis project you could say, and I need to build something based on the concept of Ohm Meter.

This is actually what I want to make, a system that measure exactly how much is the resistance of a resistor. The output would be actuating the motors to carry this resistance into another process which is sorting.

The core research starts now and I am pretty confuse with several things. I have also several things to ask, may be someone could help me out.

1. I planned to make a constant current source. From that, I could get many different Voltage Outputs when this current source is connected in series with varying Resistors.

2. The voltage then, as an input to micro controller to be processed further using voltage comparator.

3. The comparing method would also be one of many research topics I will cover here.

So engineers out there, can you please give comments or may be hints to my project? Thank you very much...

Best regards,

Kelvin - Indonesia

 

[Nigel Goodwin]

I'm not really sure what you're asking?, but passing a constant current through the resistor and measuring the voltage drop across it is a standard technique and simple.

Your main problems are mechanical, the electronics and software should be easy to do - I don't know what your course is, but this sounds rather trivial for a final project on an Electronics Degreee course?.

 

[mrfunkyjay]

I'm not really sure what you're asking?, but passing a constant current through the resistor and measuring the voltage drop across it is a standard technique and simple.

Your main problems are mechanical, the electronics and software should be easy to do - I don't know what your course is, but this sounds rather trivial for a final project on an Electronics Degreee course?.

FYI my course is Mechatronics in which, in this final project I would make an automated measurement and sorting system. The system works with resistors (different values), automatically this machine will measure and sort the resistors into their boxes. 1 10 100 1k 10k 100k for example would be 6 boxes and a carrier w/ gripper with X-Y-Z-axis would do the mechanical thingie.

 

[Nigel Goodwin]

OK, sounds a reasonable project for Mechatronics.

 

[arhi]

bit easier then making a "constant current" source is to make stabilised voltage source and then use bridge in order to get different voltages for different resistor values. Using the voltage source as the reference you can limit the error of "pure stabilisation of the voltage source"

the part where you control and build the mechanical part of the project is the complex part but should be easy for a Mechatronics major

 

[Nigel Goodwin]

bit easier then making a "constant current" source is to make stabilised voltage source and then use bridge in order to get different voltages for different resistor values. Using the voltage source as the reference you can limit the error of "pure stabilisation of the voltage source"

I would suggest you rethink that, constant current is no more difficult than constant voltage - and has the BIG advantage that the reading is linear, by careful choice of your current you can simply read the value directly in ohms.

 

[arhi]

i must admit Nigel is 100% right forgot about linearity completely

 

[Willbe]

I would suggest you rethink that, constant current is no more difficult than constant voltage - and has the BIG advantage that the reading is linear, by careful choice of your current you can simply read the value directly in ohms.

Mr. OP, what is the highest resistor value needed to be measured? That will allow you to spec the current source.

 

[Nigel Goodwin]

Mr. OP, what is the highest resistor value needed to be measured? That will allow you to spec the current source.

It might be wise to have switched ranges, easily operated automatically via the same PIC that reads them, really it depends on how practical the project is, or if a limited range is specified.

 

[Boncuk]

... and don't forget to consider resistor tolerances in your software. Otherwise the sorter won't find any good one to throw into the "pot". A 1K resistor with 5% tolerance might have any value between 950 and 1,050Ω.

Using a constant current source of 1mA the readout of the resistor will be a direct value in KΩ.

Boncuk