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single-ended vs differential input in ADC-20 & terminal boar

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single-ended vs differential input in ADC-20 & terminal boar

Postby want2know » Mon Sep 09, 2013 2:49 pm

Dear Sir/Madam,

Previously I was using ADC 20 as well as terminal board successfully for single-ended voltage measurement cause all inputs share the same ground point.

What I wanted to do now is differential input, I could not find the details in the manual on how to do it, what are the adjustments of setting in order to convert from single ended to differential?

For example, I use shunt resistor 0.01ohm as current sense, the current measurement is inaccurate due to the soldering/wire resistance added up to the shunt resistor, so what I am trying to do is using kelvin sensing where i place two additional wires as close as possible to the two ends of shunt resistor, neither of the two ends are not common ground, that explains the reason why I need to change from single-ended to differential input measurement.

Hope to hear you soon,thank you very much.
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Re: single-ended vs differential input in ADC-20 & terminal

Postby want2know » Tue Sep 10, 2013 7:31 am

Could someone please have a look?
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Re: single-ended vs differential input in ADC-20 & terminal

Postby Martyn » Tue Sep 10, 2013 8:40 am

Page 12 of the User Manual, http://www.picotech.com/document/brochures.html?id=44, will give you the pin outs of the connector with information on the differential pairs.
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Re: single-ended vs differential input in ADC-20 & terminal

Postby want2know » Tue Sep 10, 2013 2:51 pm

1. Previously I was measuring temperature, voltage and current using single-ended configurations. Now I want to use differential configuration for only the current measurement, the temperature and voltage remains in single-ended configurations. Is it possible to use the combination of single-ended and differential configurations at the SAME time in ONE setting? If yes, what are the changes needed? Else?

2. Previously I was using the input voltage range of +/-2500mV so the data logging can give me as high as 2.5V.
I read in the manual page 11, does it mean the maximum voltage measurement can be as high as 3V ? How about the ±30 V?

Common-mode range Channel to common Channel to common Common to earth ground ±1.9 V (±39 mV to ±1250 mV ranges) ±3.0 V (±2500 mV range) ±30 V

Thanks
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Re: single-ended vs differential input in ADC-20 & terminal

Postby Martyn » Wed Sep 11, 2013 6:53 am

Yes you can use a mix of differential and single ended connections, just wire according to the pin out description in the manual and configure the software appropriately. When you select a differential setting for a channel in the software, the other leg becomes unavailable for single ended use.

No the maximum measurable voltage is +-2.5V. The 3V and 30V refer to the common mode voltage outside which the unit will not operate correctly for the specified ranges.
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Re: single-ended vs differential input in ADC-20 & terminal

Postby want2know » Wed Sep 11, 2013 8:07 am

Dear Sir,

Ok, just want to be sure, I refer to the Picolog Data Logger Software manual page 58,
Differential input
If you wish to measure the voltage difference between adjacent channels, check this box.
This mode applies to channels 1, 3, 5, and 7. For example, if differential input is enabled
for channel 1, the computer will measure the voltage difference between channel 1 and
channel 2.

If I want to measure the voltage difference between the two ends of a shunt resistor, say point 'a' and point 'b', should I connect point 'a' to channel '1' or channel '2' or? how about point 'b'? where should I wire the point 'b' to?

What are the software configurations do you mean?

Thanks
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Re: single-ended vs differential input in ADC-20 & terminal

Postby Martyn » Wed Sep 11, 2013 9:28 am

What you need is "a to 1" and "b to 2" and ensure that "(a+b)/2" is not greater than the common mode voltage, 3 or 30 depending on the selected range.

When you set up the channels in the software select channel 1 and then tick the box to make this a differential reading.
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