1. How to count PMT pulses Victor Kornilov Sternberg astronomical institute I count photons 25 years.

2. Classical scheme of a photon counting Pulses from PMT A~3mV, I<10  A Pulses from amplifier to counter A~3V, I~60mA

3. Problems Both signals have the same frequency characteristics And output pulses influent at input pulses Difficulties are enlarged for pulses < 30ns Ground problem, External noise Evident solution: To count pulses near amplifier, in this case a system of data transmission into host computer needed. (Hamamatsu and ETL produce a photometric modules with RS232 interface)

4. Devices control and Data acquisition Physical layer 1 – RS485 (Recommended Standard) interface Physical layer 2 – Inexpensive components (RISC  controllers) Logical layer 1 - Exchange by bytes united in addressed packets, terminated by special signals, CRC Logical layer 2 – Nonsymmetrical structure, exchange via host only, passive, active, induced transaction Logical layer 3 – compact commands, data packets, direct access to module parameters, containers Interface boards, converters, drivers, software. We use this unnamed system 5 years (described in MASS documentation).

5. Transaction modes 1 - Command (reply signal only) 2 – Data request 3 – Active data transmission

6. Properties of the RS485 Communicate multiple nodes bi-directionally over a single twisted pair. Excellent noise rejection (differential balanced) High data rate with long cable General robustness.

7. Considerations of RS485 Configuration Termination and stubs Data rate vs cable length Cabling Fail-safe biasing Grounding and shielding Useful papers: www.national.com, Application noteswww.national.com www.bb-europe.comwww.bb-europe.com, RS-422 and RS-485 Application Note

8. Amplifier-discriminator Preamplifier - transimpendance SA5205, band 600MHz, K=9 (Philips) Pulse discrimination – Ultra fast comparator AD8611, 4ns Digital control of discrimination level Noise <200  V Deadtime with Hamamatsu R647 – 17ns, with R7400 ~10ns Permits to measure fluxes up to 10 Mp/s (if counter permits too…)

10. Counter, control and exchange Pre-counter 74HC(T)4520, fmax=60MHz Kernel -  controller ATMega8-16 2 channels with 16 bits, may be 24 bits Hardware generation of integration strobe In system reprogramming of  -programm PMT current control Exchange rate up to 2Mbit/s