1. Experimental Methods for Determining Photodetector Working Points By: Victor Rykalin Mike Smith Jim Maloney

2. Premise We need to develop a “fast” and “accurate” method for determining the working points of Photodetectors used in the Muon Tracker Detector. The most accurate methods to date also tend to take more than a reasonable amount of time given that 100+ individual detectors must be calibrated. A big problem has been distinguishing noise from signal

3. Set up LED was pulsed and measured through a strip by MRS. MRS signal run through delay and amplified by factor of 10 and attenuated and measured by ADC. Signal processed through transformer, discriminator and timing unit before used as gate by ADC.

4. Example of Measurements with MRS using 10db Attenuation and MRS Biased with 27.0 Volts

5. Example of Measurements with MRS with and without 10db Attenuation and MRS Biased with 27.0 Volts

6. Mean vs. Bias Voltage

7. Sigma for Pedestal vs. Bias Voltage

8. Sigma of Total Signal vs. Bias Voltage

9. Calculation of Actual Signal and Number of Photoelectrons σ Total ² = (σ Signal ² + σ Pedestal ²) Number P.E. = Mean/σ

10. Sigma of Actual Signal vs. Bias Voltage

11. Number of Photoelectrons Calculated from Total Signal

12. Number of Photoelectrons Calculated from Actual Signal

13. Conclusions This calibration technique allows better determination of working point of Photodetector by subtracting pedestal noise from measured signal With use of computer Macro to assemble charts of data the working point for Photodetector elements can be found in just a few hours with reasonable accuracy.