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Strange stepped output in picoscope/recorder

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Strange stepped output in picoscope/recorder

Postby cornishben » Wed Aug 12, 2009 9:12 pm

Hi,

I'm not sure if this should be in the data logger forum or the oscilloscope one..

I am using a ADC11/10 data logger and Release 5.20.7 PicoScope on Vista 32bit.

I'm trying to monitor the voltage output of a circuit (which (hopefully) is converting pulses from a flowmeter into a varying DC voltage value). When I monitor the output of the circuit with an independent DC voltmeter I can see the voltage varying in 0.01v increments, seemingly giving an 'analogue' output

But when I monitor this on CH4 of the data logger I get a stepped voltage characteristic, as shown in the attached JPG. It seems to only take on set fixed values which double up (ie 625mV, 313mV, 156mV).

Does anyone have any idea what the problem is here? I've tried varying the time/div but still see it.

I see the same stepped voltage values in Pico Recorder. I wanted to use the Meter to compare to the independent DC voltmeter, but can't get it to change in real time? (I have time/div >200ms).

I guess there is the possibility the stepped waveform is coming out of my circuit, however the DC voltmeter suggests it isn't and I can't understand why it would be...

many thanks for any help

Ben
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picoscope_waveform.jpg
Screenshot from PicoScope
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cornishben
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Postby ziko » Mon Aug 17, 2009 3:45 pm

Hmmm, at time bases of 200ms and greater the device operate in a different mode and samples at a lower rate. It could be due to this, try changing to s a quicker time base, perhaps 50ms/division.

Second thing how quick does the signal change?

Kind regards
Ziko

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