Simple edge trigger and noisy input signal

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Simple edge trigger and noisy input signal

Post by dimoto » Wed Nov 20, 2013 5:06 pm

OK, there is a low pass filter which filters the input signal.
But, the trigger is still capturing the original unfiltered input. So, the capturing will start when the trigger input sees e.g. input higher than the trigger level (mark), doesn't matter that the filtered signal is much lower:
Non filtered signal (1.png), Captured at ~1.4V.
And turning filter ON (2.png) we don't see any signal at 1.4V, but the capture is triggered... not what I want!

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Re: Simple edge trigger and noisy input signal

Post by Martyn » Thu Nov 21, 2013 7:49 am

Filtering is performed in the software after the data has been captured by the scope and downloaded to the PC, that is why it still triggers.

If you can explain what you are trying to achieve then maybe we can suggest the correct setup.
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Re: Simple edge trigger and noisy input signal

Post by dimoto » Thu Nov 21, 2013 3:25 pm

HI Martin,

See the attached example:
Non filtered noisy signal:
Raw (non filtered) noisy signal

I want to capture the voltage dip as a filtered signal :
Filtered signal, the point of interest
Unfortunately the scope triggers at any time when it sees a hidden noise peak:
Same signal, wrongly triggered at trivial, normal level
This is a common way when using "normal" digital scope (e.g. HP etc.).
This example is simplified, more real case is for example a ramping up (same type of switching noise added to the DC voltage of interest) voltage and I need to synchronize when the "DC" voltage reaches certain level.

Any suggestions?

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Re: Simple edge trigger and noisy input signal

Post by Pico Stuart » Wed Nov 27, 2013 11:05 am

Dear Dimoto,

Thank-you for your post with regard to triggering on your filtered acquisition. As Martin described triggering occurs on raw data.

Some of our products have a bandwidth limit. Please could you inform me what device you are currently using.

Bandwidth Limit: a fixed-frequency single-pole analog filter. This can be useful for rejecting noise and harmonics that would otherwise cause aliasing.

Another option would be to acquire the data over a longer period of time. PicoScope 6 has two modes of operation. Block and streaming mode. You potentially acquire a larger amount of data depending on your requirements. Please could you inform me how long you are wanting to acquire your data for. You could in theory capture a large amount of data and then apply the filter to all your data.

In streaming mode, PicoScope 6 tells the scope to capture data continuously and, at the same time, to transfer each sample to the PC with minimum delay.

At longer timebases (more than 1 sec across the screen) data is drawn on the screen at the same time as it is collected. In this mode data is "streamed" continously across the USB link.

We have made significant improvements to this USB streaming which for most devices currently on sale has increased the streaming sampling rate from 1MS/s to 10MS/s.

As well as the improved sampling rate, streaming mode uses the PC memory for waveform storage so is not limited by the buffer memory of the oscilloscope hardware. A massive 100 million samples can be collected using PicoScope in streaming mode.

The following models can now stream data in PicoScope at 10MS/s for a single channel and 5MS/s for two channels and 2.5MS/s for 3 or 4 channels: PS3204A/B, PS3205A/B, PS3206A/B, PS2205MS0, PS2206, PS2207, PS2208, PS5203, PS5204,PS6402, PS6403, PS6404, PS6407, PS4224, PS4423, PS4227, PS4224, PS4223, PS4262, PS4224IEPE.

The following models can now stream at 6.6MS/s for a single channel, 3.3M for two channels and 1.65MS/s for three or four: PS2202, PS2203, PS2204, PS2205, PS3223, PS3224, PS3423, PS3424, PS3425.

The PS2104, PS2105 and original PicoScope 3200 series (PS3204, PS3205, PS3206) are not covered by this upgrade.

This way you could capture all your data and use the Power of PicoScope 6 to zoom into the data, apply filtering and conduct further analysis.

I look forward to your response.

Kindest regards,

Technical Specialist

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