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SR250 boxcar Active Baseline Subtraction

  1. Jan 26, 2010 #1
    Hello, I have got a SR250 boxcar averager. I have got the manual, but still I dont understand how to use the active baseline subtraction. According to the manual, first I have to move the switch on the rear panel in TOGGLE position (ok, I did it). Then, in order to toggle with each other trigger, I should use the ACTIVE BASELINE SUBTRACTION output in the back. How?
    In the experiment, I have an emitting diode driven by a pulse generator. The detected light is my signal input at the boxcar. The trigger comes from the pulse generator. Unfortuantely there is a fluctuating baseline I want to get rid of. How can I connect my setup? Do I need to double somehow the frequency, so that there will be two gates, one at the signal, the other at the baseline? Or this is done by the pulse generator?
    I dont understand
  2. jcsd
  3. Jun 9, 2011 #2

    I am also using the SR250 boxcar averager in toggle mode.
    The procedure I am doing is:
    a) turn the rear switch to toggle mode
    b) Introducing to the boxcar front trigger input a trigger with twice the frequency of the trigger that drives your diode (or laser in my application). Of course, the faster trigger should be synchronized in time to the original trigger. I use a triggered function generator to produce the doubled frequency trigger.
    I believe the algorythm of the SR250 in toggle mode is as follows:
    Output averaged signal = sum on the requested number of samples (defined by the number of samples button) with alternate signs (the odd samples have opposite sign than the even samples). Divided by the number of samples.

    Good luck
    Last edited: Jun 9, 2011
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