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voltage reading and scan time of ADC11-10

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voltage reading and scan time of ADC11-10

Postby maverick » Wed Jun 28, 2006 2:33 pm

Hi,

I met two problems as follows(Use ADC11-10 with real time continous m):

(1) How to set the scan time in Picolog?
In the user manual it states "scan time is the total time to take the set of readings for a sample. The scan time should be at least three cycles at the min frequency that you wish to measure"; Now if I want to record data at sample rate of 100ms/per sample, then which scan time I should set, <100/3ms or >100*3ms?

(2) Using constant voltage from a battery, why the voltage reading output from Picolog is different from direct reading from Multimeter even though the sampling rate is the same: both are at 500ms/per sample? Additionally, it showed that voltage reading from Picolog is always higher than what got from Multimeter by around 1 or 2mv. Below are the test data I have:

Multimeter reading(mv) Picolog reading (mv)
4.9 6.7
95 97.1
518 519.5
999 1000.6

Eager to hear your reply, thanks.

Best regards,
maverick
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Postby Michael » Fri Jun 30, 2006 10:20 am

Hello,

Quite an interesting topic here.

Firslty we'll cover the scan time.
The scan time set in microseconds in PicoLog so you will need to calculate the interval in milliseconds and multiply. For the 100ms/sec you will need to divide by 3, then multiply or shift the decimal point for uSecs.

Now for the measurement voltages.
The ADC11 has an input impedance of >1 MΩ. Your multimeter probably has a much higher impedance and this is where the difference lies.

Best regards,
Michael
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