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H RBX SAFETY ISSUES C A L RBX Production Readiness Review Safety Issues and Mitigations John E. Elias HCAL Electronics Coordinator 1 March 2001 CMS HCAL RBX Production Readiness Review 1 H RBX HAZARDS C A L Low Voltage and Fire • Each box requires • 18 amps at 6.5 volts • 26 amps at 4.5 volts High Voltage • HV System is capable of 15 kV Optical Data Link Lasers • VCSELs operate at 850 nm • not visible light • but focused well by the eye 1 March 2001 CMS HCAL RBX Production Readiness Review 2 H Low Voltage and Fire - 1 C A L Wires from LV supply to the RBX (20m) • Sized for ~1 Volt drop under normal conditions • Can carry worst case fault current indefinitely without overheating • Example: 20 amps at 1 volt drop nominal • RBX ground fault at LV supply max. current gives power = VxI = 7.5Vx26A = 195 W which is only10 W per meter of wire • Current limiting features built into the LV supply are adequate to mitigate the hazard 1 March 2001 CMS HCAL RBX Production Readiness Review 3 H Low Voltage and Fire - 2 C A L Readout Cards • Each card has access to the full power supply current via the backplane in event of a fault • Mitigations • Current limiting feature in voltage regulators • PolyFuse protection at point of entry Polymeric positive temperature coefficient device for overcurrent and overtemperature protection Resettable – power down 1 March 2001 CMS HCAL RBX Production Readiness Review 4 H Low Voltage and Fire - 3 C A L Sample Draw System Planned • Continuously monitors air sampling system for fumes and aerosols, “sniffers” • Break detector into many monitor zones • Multi-level alarming • Off normal – check into it • Seriously off normal – do something now • Corroboration by other system – fire alarm • Provision for automatic shutdown of the low voltage system • Individual RBX basis • Entire half-barrel, end cap or HO basis 1 March 2001 CMS HCAL RBX Production Readiness Review 5 H High Voltage - 1 C A L Power Supply Bleeder Box HV (5) Return Current Bleeder resistor Return Current BV (5) Safety resistor Z HV Cable, 150 m long (5 HV & 5 BV conductors) RBX HV Unit Safety resistor HV Back plane Readout Module HV Filter resistor HPD 1 March 2001 CMS HCAL RBX Production Readiness Review 6 H High Voltage - 2 C A L RBX HV Module 1 March 2001 CMS HCAL RBX Production Readiness Review 7 H High Voltage - 3 C A L RBX High Voltage Distributor (Backplane) 1 March 2001 CMS HCAL RBX Production Readiness Review 8 H High Voltage - 4 C A L 3 & 4 CONDUCTOR SUB-CABLES 26 AWG, 2 / 3 kV (AC/DC) SINGLE WIRE O.D.= 0.051”/ 1.3 mm 5 SINGLE WIRES 26 AWG, 8 / 12 kV (AC/DC) O.D.= 0.118”/ 3.0 mm BINDER WRAP & BRAIDED SHIELD PROTECTIVE JACKET 0.05”/1.2 mm O.D. = 0.484” / 12.3 mm 1 March 2001 CMS HCAL RBX Production Readiness Review 9 H High Voltage - 5 C A L 10 Energy Stored in the KERPEN HV Cable. 5 HV wires, 150 m, 51 pf/m, total of 40 nf and 25 nf of the power supply output capacitance. 9 8 CERN safety limit for a capacitive discharge is 10 J (TIS, IS 28) Energy (J) 7 6 Far End Energy (Power S. + Cable) 5 Near End Energy (Power Supply) 4 3 2 1 0 0 2 4 6 8 10 12 14 16 18 20 Voltage (kV) 1 March 2001 CMS HCAL RBX Production Readiness Review 10 H High Voltage - 6 C A L High Voltage Summary • Connectors have deeply recessed contacts and are rated for 30 kV • Safety resistor potted in series at RBX end of the cable limits maximum discharge current to 1 mamp per wire at 10 kV • Stored energy in the cable (all five wires) is 6 Joules at the maximum supply voltage • Maximum power supply current capability is 40 microamps • A 250 meter length of cable has been held at 20 kV for one year (accelerated testing) with the leakage current unchanged at < 10 pamp 1 March 2001 CMS HCAL RBX Production Readiness Review 11 H Laser Diode - 1 C A L VCSELs drive the optical data links • Optical power is 1.8 mW typ. • But the 850 nm light is not visible and this overrides the power consideration and makes it hazard class 3b “can cause eye injury in less than 0.25 sec” 3 mm long 1 mm dia. • Glued to ~15 cm long connectorized fiber 1 March 2001 CMS HCAL RBX Production Readiness Review 12 H Laser Diode - 2 C A L Intrinsically eye-safe Strategy 1 • Glue a permanent attenuator in fiber pigtail to make the link intrinsically eye-safe at the front panel connector of the Readout Module • Unkown – whether the light level at the receiver is adequate for good link performance • Known – the TTC optical links are intrinsically eye-safe and perform very well Intrinsically eye-safe Strategy 2 • Use a spring loaded shutter on the front panel connector of the Readout Module • Unknown – whether shutters exist for ribbon connectors or a custom add-on is needed • Known – it will be costly 1 March 2001 CMS HCAL RBX Production Readiness Review 13 H Laser Diode - 3 C A L Eye-Safety on the workbench • The laser and fiber pigtail are removable from the printed circuit board with two fasteners Work to be Done • Detailed power density analysis using the beam power profile versus angle • Determination of the minimum safe distance between the fiber end and the eye surface Commitment – intrinsically safe system • Administrative procedures may still be needed but they are not the principal mitigation 1 March 2001 CMS HCAL RBX Production Readiness Review 14