Electronics > Beginners
Is there someting to improve in this design? - Milliohm meter
<< < (3/5) > >>
MasterT:

--- Quote from: Arek_R on November 11, 2018, 10:44:31 pm ---So throw away current adjustment 100R pot and do it in software?
That's a good idea, thanks.

--- End quote ---

It's more than kick-off one pot. What I'm trying to say, design concept shown in the video was good in the past century, in 80-th & 90-th.  Precise reference, precise current source, same with voltmeter. It cost a lot. Having uCPU, you don't need all this analog precision, as song as it's not drift much in the minutes time frame. Using only one precise resistor in the circuits and doing comparative measurements by dual channel ADC, ads1115 , ads1232 etc, you can greatly reduce the cost of this project.
Arek_R:
Yes yes one resistor, that's what I mean :p
What do you mean by "comparative measurements" ?
MasterT:
This picture explains:

https://www.quora.com/How-can-we-measure-the-value-of-resistance-with-CRO

Measure V and Vm using dual channel adc resistance can be calculated w/o knowing a current, since it zeroed out  of equation.
spec:

--- Quote from: MasterT on November 11, 2018, 10:54:55 pm ---
--- Quote from: Arek_R on November 11, 2018, 10:44:31 pm ---So throw away current adjustment 100R pot and do it in software?
That's a good idea, thanks.

--- End quote ---

It's more than kick-off one pot. What I'm trying to say, design concept shown in the video was good in the past century, in 80-th & 90-th.  Precise reference, precise current source, same with voltmeter. It cost a lot. Having uCPU, you don't need all this analog precision, as song as it's not drift much in the minutes time frame. Using only one precise resistor in the circuits and doing comparative measurements by dual channel ADC, ads1115 , ads1232 etc, you can greatly reduce the cost of this project.

--- End quote ---

What a brilliant approach- thanks for posting :)
David Hess:
It would be a major design change but I would chop the excitation and synchronously demodulate to remove thermocouple errors.  Essentially this means reversing the test current between positive and negative and doing the same on the sense leads.  Otherwise it is not possible to take advantage of the accuracy (low drift) of even modern bipolar precision amplifiers never mind chopper stabilized amplifiers.

This is commonly done in high end multimeters which provide milliohm resistance measurement.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod