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Cycling channels On and OFF over time

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Cycling channels On and OFF over time

Postby BSI » Tue Mar 20, 2012 6:15 pm

I am using a Pico 4227 for an application that requires the device to be operating hours at a time. The general procedure being implemented is a Rapid Block Mode acquisition at 250MS/s (1 ch) or 125MS/s ( 2 ch) and filling up the buffer with a few thousands points at most, repeatedly ~ 500 times every cycle. The operation takes in the order of a few seconds before it is resumed again. Now working with 2 channels, and having meaningful data coming in alternatively one channel at a time ( chA, chB, chA, chB etc...) I am working on a trigger scheme that for each cycle also alternates which channel is used as trigger input. It looks like this:

Scheme 1: f = 250MS/s, effectively producing f = 125MS/s since 2 channels are turned on, both channels always ON.
    t=i --> Trig on chA, acquire chA & chB, get rid of data from chB
    t=i+1 --> Trig on chB, acquire chA & chB, get rid of data from chA
etc...

Scheme 2: f = 250MS/s , only one channel on at one time.
    t=i --> Turn off B, turn on A, Trig on chA, acquire chA
    t=i+1 --> Turn off A,turn on B, Trig on chB, acquire chA & chB
etc...

Scheme 2 produces a higher freq data which is better. However, turning on and off the channels produces some overhead, but I am mostly concerned about the robustness of the clicking switch/relay operating every time this is done. I am talking about 1000 times a day... What would you recommend?
Note that I initially was considering using logical triggering, but I had issues with it (separate post in software/LabVIEW forum), plus it does not help on the sampling rate front. I also considered using ETS, but according to the specs it only works with Block Mode, not Rapid Block Mode...

Thx.

Laurent
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Re: Cycling channels On and OFF over time

Postby Martyn » Tue Mar 27, 2012 9:48 am

The decision will really depend on which is more important to you in terms of sample rate or wear/tear of the device. Another solution would be to drive two scopes from your application.
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Re: Cycling channels On and OFF over time

Postby BSI » Tue Mar 27, 2012 6:40 pm

I understand that, but I do not know the specs of the device in question with regards to turning on and off a channel. So this is the part I need your help for. Essentially what is the # cycles the ON OFF relay (if it is a relay) in the 4227 can take? There should be a spec for this.

Thx
Laurent
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Re: Cycling channels On and OFF over time

Postby Martyn » Wed Mar 28, 2012 9:31 am

The relays are specified for 20 million operations.
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Re: Cycling channels On and OFF over time

Postby BSI » Thu Mar 29, 2012 3:33 pm

Thx !
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