[Halld-tracking-hw] CDC measurements

[Fernando J. Barbosa]

Hi Naomi,

Ok, that explains it.

Thanks and best regards,
Fernando




Naomi Jarvis wrote:
> Hi,
>
> The amplitude plots end at 2200ch because the preamp output does not 
> go much above (approx) 0.5V and the fADCs were set up with a range of 
> 1.1V and a small negative offset.
>
> Just to make sure of this, I put a square wave into them (example 
> attached) and calculated channel 0 is -220mV and 4096 is 870mV for ADC 
> channel 1.
> The shaper output was set to put the baseline at around -130mV, 
> channel 300 for channel 15 (our most convenient straw for Fe55 access).
> There are example scope traces on the wiki under Preamp4 'scope 
> traces.   We have not been using the interposer board for any of these 
> measurements.
>
> To match the final fADCs range, we reset our fADCs today so that the 
> gain is halved, and remeasured with the square wave again.  We now 
> have channel 0 at approx 50mV and channel 4096 at approx 600mV 
> (example attached - the voltages were measured on the 'scope). The 
> shaper output is now set to put the baseline at 80mV.
>
> We are collecting cosmic data with this new range over the weekend.
>
> Best regards,
>
> Naomi.
>
>
>
> Fernando J. Barbosa wrote:
>> Hi Naomi,
>>
>> I am still puzzled by the fact that your amplitude plots show a limit 
>> at ~2200 channels. Could this be because of a combination of the 
>> shaper offset and the dynamic range of the ADC you have?
>>
>> If I understand your setup, the ADC has a negative polarity range 
>> (-1V?) and the output from the shaper has positive-going pulses into 
>> the ADC. You set the shaper offset negative so that the baseline is 
>> at the highest scale of the ADC and a large pulse would underflow. 
>> You then perform the subtraction off line. Is this correct?
>>
>> Thanks and best regards,
>> Fernando
>
>
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