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Picoscope 6403A sampling problem

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Picoscope 6403A sampling problem

Postby Toni » Fri Dec 19, 2014 3:54 pm

Hello,

I recently find there is a sampling problem of the Picoscope which is very annoying.

For example, if I send a 1 kHz sinusoid signal generated by Picoscope itself, when the sampling frequency is set at 1 MHz for a 2-second signal displayed on the screen (i.e. 2 million samples), the actual number of samples is 1’990’450, that is 9’550 points less. I have no problem with that, because it seems a hardware restriction of the Picoscope.

But the actual timing is not right either. I read the data using MATLAB (8-bit Picoscope vertical resolution).
The following data are the values read from MATLAB. T is for time, and A is for the amplitude of the captured signal.

T(1) = -1.0048 μs, T(2) = 0 s, T(3) = 1.0048 μs, ... , T(end) = 2 s + 2.09 μs.
A(1) = -0.0157 V, A(2) = 0 V, A(3) = 0 V, A(4) = 0 V, A(5) = 0.0157 V, ... , A(end) = -0.0315 V.

T(1) is equal to Tstart, and T(end) is equal to Tstart+(Length-1)*Tinterval;
A(1) to A(end) are the corresponding reading of the signal amplitude.

Apparently, by observing the values of T, the signal does not start from 0 second, and does not end at 2 second. It seems that the signal has been stretched slightly. Also, the amplitude does not start at 0 V, or end at 0 V.

Do you have any solutions for this? Thanks.

Toni
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Re: Picoscope 6403A sampling problem

Postby Hitesh » Mon Dec 22, 2014 1:11 pm

Hi Toni,

The PicoScope 6 software will determine the sampling interval to use and the number of samples it can collect in the time window specified.

A few extra samples are collected to assist with ensuring that the trigger position is correctly displayed on the screen. This and the sampling interval used will impact on the T(1) and T(end) values as these will be relative to the trigger point.

If you click Views -> View Properties, what are the values for sampling interval and number of samples?

One alternative might be to collect the data directly from the PicoScope device into the MATLAB environment using our Instrument Driver Package (download the Software Development Kit from http://www.picotech.com/software.html

Regards,
Hitesh

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