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125°F (5 to 53°C). The calculations are based on a simple series reliability model, where a single component failure causes the failure of the whole assembly. The failure rate and the mean time before failure (MTBF) for each assembly are listed in the table below. 8.3 System MTBF Calculation If a system includes additional modules, the total system MTBF may be calculated by adding the individual module failure rates for a total system failure rate expressed in failures per 1,000,000 hours. The system MTBF is then calculated by dividing this total into 1,000,000 hours. , The Ronan TRS -76 Tank Monitor is a highly reliable, multimodule system, designed to monitor leakage of liquid or vapor on tanks and piping. The system operates in fail-safe mode, providing continuous self -check, as well as manual checking capabilities. The logic and control circuitry is arranged so that, in the event of internal failure, the control function transfers into safe position and an alarm sounds, indicating system failure. For example, if the turbine control relay circuit fails, the turbine starter coil will drop out, if it was energized. With the control relay contact closed and the product dispenser switch closed, the alarm horn sounds, indicating module failure. The system consists of the dispenser module, annunciator module and the horn and pushbutton module, in numbers to be suplied in the system as required. 8.4.1 Dispenser Module: The dispenser module accepts pressure switch input and product dispenser switch, providing product line leak indication and turbine starter coil control. The module consists of two sections: solid-state circuitry and relay -driven logic. The solid-state circuitry is designed to generate delayed signals for time delay relays. All time delay relays must be adjusted to required time by the front -panel - mounted potentiometers. The on -board power supply used to power -up the solid-state circuit is transformer isolated, converting 115 VAC to regulated 12 VDC. The remaining circuit on this module is relay -driven logic, operating at 115 VAC. 8.4.1.1 Protection Feature: The leak sensing device (pressure switch) is hard -wired in the normally open position. With increasing pressure, the switch closes (13.5 to 16 psig). This closure permits the turbine to run beyond the four -to -six - second delay. Should switch fail electrically or mechanically, it will not provide the switch closure and, thus, turbine will shut down after the six -second delay. The TRS -76 will then provide an alarm via lamp indication and the sound of the horn. Should the field wiring be broken or shorted to ground, the same will occur. A failure on the dispenser module will prevent start-up of the turbine and the horn will sound when the dispenser module is called to start via product dispenser. A failure will only affect the product in which that failure occurred. All other product dispenser modules will still be monitored and allowed to run. 8.4.2 Annunciator Module: The annunciator module is a three-point module, accepting normally closed field contacts. It is all relay - driven logic, operating from 115 VAC power, providing long -life performance already proven in Ronan relay -driven alarm modules. The module provides the ISA -A sequence without the flashing signal and one alarm lamp output for each input field contact and a common horn trouble contact for each module. 8.4.3 Horn and Pushbutton Module: The horn and pushbutton module is a simple interface module between the rear terminal bus and the front -panel pushbutton and horn. Module Failure Rate/10E6 Hours MTBF Hours X76 Dispenser Module 13.429 74,467 X76 Alarm Module 3.697 270,470 X76 Pushbutton and Horn Module 0.027 36,630,000 X76 Intrinsically Safe Power Supply 0.398 2,512,600 Total Failure Rate: 17.551 Failures/10E6 Hours System MTBF: 56,976 Hours Table of Results