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Entry  Tue Mar 1 19:03:37 2022, Keita Mizukoshi, Scaler issue to evaluate live time  
    Reply  Thu Mar 3 16:14:16 2022, Stefan Ritt, Scaler issue to evaluate live time  
       Reply  Fri Mar 4 03:55:33 2022, Keita Mizukoshi, Scaler issue to evaluate live time  pulse_example.pngrate.png
          Reply  Mon Mar 7 16:37:54 2022, Stefan Ritt, Scaler issue to evaluate live time  Screenshot_2022-03-07_at_16.37.32_.pngScreenshot_2022-03-07_at_16.35.44_.png
Message ID: 874     Entry time: Mon Mar 7 16:37:54 2022     In reply to: 870
Author: Stefan Ritt 
Subject: Scaler issue to evaluate live time  

I tried your measurement with the DRSOscilloscope app (see below), and I measure a constant difference of 10 Hz among the whole range of 100 Hz to 3 kHz.

So I don't know what's wrong on your side. Did you try with the oscilloscope app as well? Have you checked your pulse generator? The evaluation board time reference is a quartz with an accuracy of 10^-5, so no way one can get there a difference you see.


Keita Mizukoshi wrote:

Thank you very much for your explanation.


I would like to show you a pulse example ('black line is the threshold).

Still, pulse generator rate and DRS4 rate are a bit different more than 10 Hz.


Stefan Ritt wrote:

The scalers are read out 10x per seconds, so they have an accuracy of 10 Hz. I tried a 50 Hz pulser, and measured 40 Hz, I tried 52 Hz and measured 50 Hz. This is about what you can expect.

The scaler rate is measured after the discriminator of the trigger, so the trigger level also affects the scaler reading. If you have a 100 mV pulse and your threshold is 200 mV, your scaler rate drops to zero. That can be seen best with the DRSOsc and sliding the trigger value. If you have a 50 Hz pulse with narrow (< us) pulses, things are fine. But if you use a 50 Hz square wave, then you get distorted signals due to the AC coupling which can also be confusing. See for example here: https://www.daqarta.com/dw_gg0o.htm

Keita Mizukoshi wrote:

Hi. I'm trying to evaluate livetime of the evaluation board with the hardware scaler. I'm facing a strange issue.

I took the rate with the function, DRS->GetScaler(int channel).
I guess that channels 0--3 mean the rate for the channel, and channel 4 means the counter of the trigger.
I took the 1,000 pulses generated by a pulse generator with 50 Hz.
The scaler values are ~ 39.83, not 50.
The timestamp difference between the initial event and the final event is 19.98 seconds.
1000/19.98 ~ 50, thus, the evaluation board took the pulses with enough livetime.

Can we believe the scaler value for the livetime evaluation?




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