Trip point

Trip Valves The trip valve is part of a system that is used where a specific valve action (i.e., fail up, Fail down, or lock in last position) is required when pneumatic supply pressure to the control valve falls befow a preset level. Trip systems are used primarily on springless piston ac tuators requiring fail-open or fail-closed acrion. An air storage or Volume tank and a check v ve are used with the trip valve to provide power to stroke the valve when supply pressure is lost. Trip valves are designed with hysteresis around the trip point to avoid instabihty when the trip pressure and the reset pressure settings are too close to the same value. 

For a 20 percent overcurrent trip point, lower this resistance by 20 percent or a resistor value of 56 ohms. 

The same system, but with an on-off pressure switch set to activate the emergency shutdown system if the pressure reaches the predetermined point. The pressure switch remains inactive as long as the pressure is below its trip point. 

Disadvantages Poor zener diode accuracy (5% initial tolerance) creates errors in trip points other circuit variants more precise... 

FLA Full-limit amps, or the high-amperage trip point for a motor. 

The actual test is performed by operating the process to the trip point, and ensuring that the intermediate relays and instruments respond properly. The simulated test is used in circumstances in which the instruments are of a nature that create a forced shutdown or startup in a very hazardous process. The simulated test is also used if the instrument schemes are so complicated that the interlocks cannot be checked on a single-trip shutdown. [26]... 

Uncontrolled rod withdrawal from startup to trip point with delayed manual trip 3... 

The Neutron Flux Monitor System comnonly referred to as the "Beckmans"I is composed of four picoammetersi ion chambers and controllers for setting safety circuit trip points. The four ion chambers are located in instrument risers beneath the reactor and are positioned for equilibrium power level calibration ... 

The Gamma Monitor System detects fuel element ruptures by continuously monitoring effluent water from each rear cross-header. A gamma sensitive Ion chamber la revolved past the respective continuous streams and measures the magnitude of the gamma emission. Vlstial fluid audible Alarms eumunclate if the trip points are exceeded. radiation profile of the crossheaders Is plotted on multipoint recorders. 

Consider the example of a safety instrumented function to protect against vessel rupture due to over-pressure. When high pressure above the trip point is detected, the function will do three things ... 

The period of time between a trip point being reached and a hazardous event occnr-ring if no safety measures such as a shutdown are taken. 

To calculate the reduction in the radios of coverage due to concrete at a given detector trip point, Eq. (I) riiould be evaluated, where X equals zero and R - Rq, the radius of coverage for a steady-state excursion at the detector trip point. Rd can be obtained from Appendix B of the proposed standard on criticality alarm systems. The result of the% substitutions gives... 

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