March 2013

Date : 1st March 2013 (K.Allada)

For an accurate deadtime calculation we need to turn on TI readout. It will tell us how many triggers are received.

Things to do:

1. Turn on TI readout
2. Learn to access trigger counts from TI readout (Bryan said he maybe able to provide a routine to access trigger counts..check with him again)
3. Also check tiStatus() routine if it has anything useful in terms of trigger counts
4. After 1-3 is finished, check to see if FADC trigger counts match-up with TI counts. Otherwise we have problem?
5. Add both TI and FADC trigger match into the decoder and provide deadtime calculation

Date : 1st March 2013 (R. Michaels)

Scan of Deadtime and Asymmetry.

Using Kalyan's deadtime calculation, now embedded in my version of the code, I made a rate scan to see how the deadtime changed and what happened to the asymmetry.

Definitions
F+ = rate when helicity bit is true
F- = rate when helicity bit is false
Favg = DAQ rate (should be average of F+ and F-)
A_pred = (F+ - F-)/(F+ + F-) = predicted asymmetry
A_obs = observed helicity in data
DT = deadtime reported by Kalyan's algorithm
DNR? = if "Y", there were "Data Not Ready" printouts by the event list.  If "N" there were none.

Run ... avg F ... F+ ... F- ..... A_pred .... A_obs ..... DT ..... DNR?  
.......... kHz ..... kHz ........... % ....... % ......... %
2056 ... 280 ... 276.2 .. 285.9 .. 1.73 .... 1.01 ..... 0 ..... N 
2060 ... 239 ... 236.8 .. 246.3 .. 1.97 .... 2.35 ..... 0 ..... N
2063 ... 311 ... 306.8 .. 316.2 .. 1.51 .... 0.03 ..... 47.7 .. Y
2066 ... 330 ... 323.1 .. 332.3 .. 1.40 .... 0.01 ..... 53.3 .. Y
2068 ... 421 ... 418.3 .. 427.6 .. 1.10 .... 0 ........ 78.7 .. Y
2071 ... 218 ... 216.4 .. 226.1 .. 2.19 .... 1.22 ..... 0 ..... N
2073 ... 138 ... 135.8 .. 145.9 .. 3.58 .... 1.53 ..... 0 ..... N

Comments

The deadtime (DT) skyrockets at a critical frequency. I don't think I could get a small nonzero deadtime (e.g. 5%).

The presence of nonzero DT causes the Asymmetry to be completely diluted, by a far larger factor than you'd expect. Expect a dilution factor of 1-DT

A_obs often does not agree with A_pred. The other day (late Feb entry) this was also true, though one is sometimes greater and sometimes less than the other. Not clear why.

I am not convinced we are measuring the DT correctly. Need a second, redundant method.