Welcome to the filtering video that supports our news letter article
Training material regarding filtering
We are going to look at the typical lambda sensor so we are at automotive
Sensors
Lambda
And then zirconia
A notorious sensor for noise
Here is the help file displaying what it should look like
But in reality we all know that when we press the record button
There we have it notoriously noisy signal 0.1 to 0.9 Volts
We need to activate a feature called hardware filter or band width limiter
And that is available with 4425 or 4225 scopes
You can see that that is available under tools
Preferences
Options and there we want
Show analogue options
Apply and OK
Now open up the channels options menu
And you will see 20k/Hz bandwidth limit
That has removed a large proportion of the noise you can see that already
So we were plus or minus 1 Volt
But noise would exceed 20 Volts so that has quenched it quite a lot
Be aware though that when the band width limiter is activated
There is no going back so the signal is simply not allowed to pass
Through into the scope for processing so
It is not like you can turn it off and reveal the original signal
To keep all that noise in check we will change the scale to 20 Volts
Which seems excessive I know for a .1 Volt signal
But plus or minus 20 Volts with 5 times vertical zoom
So we now have a plus or minus 4 Volt scale
And we can see lambda switching there
So the noise is still present
But we have utilised a large range to keep the noise in check
And we will activate low pass filtering
So now channel options A
Scroll up to 100Hz
And there you can see the unfiltered waveform
Which is updated right at the end of the buffer
Momentarily we will show you the filtered waveform
Now to see both at the same time we can go
To tools and preferences
And we can activate a feature called display previous waveform buffer
So what is going to happen now when we apply this feature
You will see the previous waveform to the right and that is filtered
Unfiltered to the left
So there we have the unfiltered waveform coming through
On the right hand side is the waveform from the previous buffer
So that is a nice feature there so you can actually see
Both on one screen at the same time
Without having to wait for the wave form to update at the end of the screen
Before it momentarily shows you the waveform
Or alternatively stop and go through the waveform buffer
Because obviously every waveform now inside the buffer is filtered
So for improved resolution we can increase our vertical zoom by 20
So there we have plus or minus 1 Volt
You can clearly see oxygen sensor switching from .8 to .1
And return that back to where we were which was times 5 vertical zoom
Just bring the scale up so we are central and zeroed
OK now switch off low pass filtering
So there we have our unfiltered waveform running exactly as we did before
We still have display previous waveform buffer activated
So we go to tools
Preferences
Sampling
And remove the feature display previous waveform buffer
There we have it
Plus or minus 20 Volt range
Unfiltered with a times 5 vertical zoom
Our alternative option for filtering is maths channels
Tools then create
Click next and then click on advanced
And it is filters that we want
And low pass and it is channel A of course as we are only measuring on channel A
So it is channel A comma 100
So that is a low pass 100 Hz filter on channel A
We want to override the voltage ranges so we go to minus 2 Volts and plus 2 Volts
That will give us great resolution
Tick the box adjacent to the low pass A 100 maths channel
And there you have it
It will appear on screen
At the end of the waveform buffer
So there we have our live unfiltered
And the maths channel is of course the previous waveform
Notice we have a different scale there
Vertical zoom times 2
Gives us now plus or minus 1 volt on the maths channel so we can clearly see
Oxygen sensor lambda sensor switching
Now you can customise your maths channel
So we have called it low pass A
There is nothing stopping us calling that whatever we like
Because we can customise or rename or amend using the edit feature
So we will call this lambda
So that will always now appear in your library as lambda
And that can be activated any time you are measuring a lambda sensor
Tools
Maths channels
And then in your library click on lambda
And to deactivate it
Once again tools
Maths channels and uncheck the box adjacent to lambda
Switch back to a low pass filter
And lets capture some data
You see the filtered waveform there it updates right at the end of the waveform buffer
Lets just capture a little more data
So the lambda sensor signal unfiltered
Then momentarily we see displayed as filtered
Scroll back through the buffer and there is our filtered waveform
Now be aware of over filtering so reducing the filtering level down to 2 Hz
Virtually makes this waveform unrecognisable
So there we have an oxygen sensor signal
When we over filter we loose so much detail
Default value 100 Hz for low pass
So whether it is a low pass filter activated under the channel options here
Or a low pass filter set within a maths channel 100 Hz
So another new feature or additional feature of PicoScope
Is add view
So here we have two views
We can arrange these in rows or columns
So you can see the upper waveform is our oxygen sensor signal with the filter activated
Filter is present and momentarily displayed at the end of the screen
Bottom screen is the original settings so you see there is a 20 Volt scale there
We need to change that to times 5 vertical zoom
So there we have both waveforms running across the screen in two separate views
So we have two sets of controls for each view it could be that you may want to place
Channel B or C or D on your lower view and your oxygen sensor in the upper view
So we can also activate display last wave form buffer
Exactly the same as we did in the previous demonstration
So that is under the tools menu
Tools
Preferences
Sampling and display previous waveform buffer OK
And there we have it
Duplicate waveforms
Separate views
Unfiltered on the left
Previous filtered waveform on the right
So to close the views
Views
Close view reverts us back to our original capture
There is nothing to stop you from sticking to the 1 Volt scale
Resetting the zoom
Remember the hardware filter is on at this stage
But for a simple capture
Low pass 100 Hz filter
Stop capture
And scroll through the buffer
So it is very simple with numerous options at our disposal