10 Bit Resolution

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medelec35
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10 Bit Resolution

Postby medelec35 » Tue Mar 30, 2010 6:48 pm

Data sheet covers 8 bit ie
Analogue conversions
Analogue conversions have a resolution of 50mV (20
counts per Volt). This allows simple calculations to be
used to convert the results of an analogue sample into a
direct voltage representation - simply divide the input by
20.
Analogue conversion of input voltages above 12V will
return the value of the clamping voltage (between 241
and 255)

What about details for 10 bit analogue sampling please?
According to my voltmeter, minimum resolution was 20mV. But since 1V = count of 80, this did not make sense.
Thank you.
Martin

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Re: 10 Bit Resolution

Postby Benj » Wed Mar 31, 2010 9:09 am

Hi Medelec,

The MIAC has a 10-bit resolution of around 80 counts per volt. Therefore your reading is correct.

I got this result by

255 / 20 = 12.75

1023 / 12.75 = 80.235

Thats a resolution of around 12.46mV per count.

I think the minimum resolutaion may be effected by the op amps but im not sure about this one. Sean would be able to give you more info.
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Re: 10 Bit Resolution

Postby medelec35 » Wed Mar 31, 2010 12:16 pm

Thanks Ben. I worked out min resolution is approx 12.5mV (1/80). That’s why min resolution of 20mV did not make sense. What you say about the amplifiers sounds logical and thanks for correction to 12.46mV. (I was not that far out :P )
Martin

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Re: 10 Bit Resolution

Postby Sean » Wed Mar 31, 2010 2:51 pm

I have posted a reply to a similar question in a adjacent topic.

http://www.matrixmultimedia.com/mmforums/viewtopic.php?f=28&t=7256&p=18122#p18122

The resolution of the MIAC ADCs should not be affected by the input circuitry, but the accuracy of the applied voltage will be limited by the 1% tolerance of the values of the resistors used in the input dividers.

In general, an accuracy of approximately 1% can be expected, allowing 10V to be displayed with 1 decimal place of accuracy (10.0V). This makes full use of the 8-bit ADC conversion, which has been set up to convert 12V to a value of 240 (50mV per step).

Sampling in 10-bit mode will improve the resolution of the sampling of the voltage being applied (precision), but will not improve the absolute accuracy beyond 1%. 10-bit mode is of more use tracking changes in voltage rather than absolute voltage.

The MIAC input circuit produces an ADC conversion value of 960 when 12V is applied - 12.5mV per step (Medelec, you were right!). The 1% tolerance of the input resistors, coupled with the potential for a small offset voltage generated by the op-amps, could lead to errors when measuring very low voltages.

These are common instrumentation issues that are covered in many control documents and ADC data sheets.
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Re: 10 Bit Resolution

Postby medelec35 » Wed Mar 31, 2010 5:30 pm

Thanks Sean. That is very useful information!
Martin

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