Mains filter for short recordings

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kmichel
Posts: 5
Joined: Mon Mar 10, 2014 10:57 am

Mains filter for short recordings

Postby kmichel » Wed Oct 14, 2015 1:31 pm

Hello,
in Practical courses with students we do recordings of muscle compound action potentials in response to nerve stimulation or during knee jerk reflex. The recording episodes are always triggered recordings with durations of only a few hundred milliseconds. Although the recording in principle works fine (we see nice compound action potentials), the signals are often heavily contaminated with mains noise (50 Hz in our case). Switching on the mains filter in the input amplifier dialog doesnt help because the recordings are too short. Is there any other way to reduce this noise?
This is the first experiment that the students do and i think it would be motivating if they could see nice signals without too much effort :)

Thanks for any help!

Klaus

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tbroughton
Posts: 133
Joined: Mon Mar 25, 2013 8:28 am
Location: United Kingdom

Re: Mains filter for short recordings

Postby tbroughton » Tue Oct 20, 2015 3:07 pm

Hello Klaus,

Your best option here is to use LabChart's Digital Filters to allow you to Filter the signal post-recording. Digital Filters can be turned on or off at will, so your raw signal will not be affected.

To access the Digital Filter option within LabChart, choose an unused, and click the Channel's name at the right-hand side. From the resulting drop-down menu, choose Digital Filter - this will allow you to apply a variety of filters without affecting your recording. You can use a narrow band-stop filter to mimic a 50Hz filter.

I hope that helps!
Tom Broughton
Education Support Specialist | ADInstruments Europe

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kadams
Posts: 88
Joined: Fri Feb 19, 2010 12:32 am

Re: Mains filter for short recordings

Postby kadams » Thu Oct 22, 2015 2:32 am

In case you find using a Digital band-stop or notch filter does not work as effectively as the Mains Filter, it is often possible to setup LabChart so that the PowerLab is sampling continuously even though you are using a fixed duration triggered mode.
LabChart will generally use this continuous sampling mode unless the Stimulator is turned on, in which case it has to stop and start the PowerLab for each block so that the Stimulator starts at the start of the recording.

However, if in the Sampling dialog you set the Trigger Source to Stimulator, then LabChart can use the continuous sampling mode even though the Stimulator is running, with the result that the Mains Filter should be usable.

I have attached a LabChart file that demonstrates this setup. For this recording I had a short wire “aerial” attached to input 1 and the Stimulator output connected to input 2.
Attachments
MainsFilterContinousSamplingMode.adicht
(153.5 KiB) Downloaded 420 times
Kit Adams Ph.D
Chief Architect Windows, ADInstruments, New Zealand

crossby
Posts: 2
Joined: Sat Nov 26, 2016 9:37 am

Re: Mains filter for short recordings

Postby crossby » Sat Nov 26, 2016 9:39 am

This is excellent, thank you - I will have a go at it!
คาสิโนออนไลน์
Best wishes,
Crossby

MosheBlackwell
Posts: 1
Joined: Wed Dec 07, 2016 5:05 pm

Re: Mains filter for short recordings

Postby MosheBlackwell » Wed Dec 07, 2016 5:08 pm

kmichel wrote:Hello,
in Practical courses with students we do recordings of muscle compound action potentials in response to nerve stimulation or during knee jerk reflex. The recording episodes are always triggered recordings with durations of only a few hundred milliseconds. Although the recording in principle works fine (we see nice compound action potentials), the signals are often heavily contaminated with mains noise (50 Hz in our case). Switching on the mains filter in the input amplifier dialog doesnt help because the recordings are too short. Is there any other way to reduce this noise?
This is the first experiment that the students do and i think it would be motivating if they could see nice signals without too much effort :)

Thanks for any help!

Klaus



I think it's a great experiment for students :)


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