Relay logic

For example consider a SIS comprising a single switch, relay logic and a single final element which yields a system with a PFDg g of 7,7 x 10 . This system achieves a risk reduction of approx. 1,3 x 10. ... 

When the first programmable electronic equipment, called programmable logic controllers (PLCs), were created as an alternative to relay logic, many engineers immediately believed these new devices would be perfect for automatic protection applications. They felt that the functionality of these electronic devices encompassed aU that would be needed and more. 

Can a relay logic system be used to satisfy the requirements for a SIL 3 Safety Instrumented Function What are some of the issues that need to be addressed in using relays as a logic solver ... 

Table 12-1. SIL1 Case 1 - Pressure Switch, Relay Logic, Solenoid Valve, and Trip Valve...

ESDI is located at the well and consists of pressure switches, relay logic, and the flow-line valve. This trip system closes the flow line valve automatically if the line pressure drops below or goes above... 

Logic - For ESDI, relay logic is used. For ESD2, a safety PLC is installed. 

Since 1970 considerable changes have taken place in the means by which processes are controlled. Pneumatic controllers and relay logic have been replaced by solid-state logic and more recently by programmable logic controllers. During the same time the cost of the hardware has fallen and the availability of appropriate software has increased while other process costs have risen. The inclusion of such equipment has therefore become more easily justifiable. 

Electromechanical panels that use relay logic to sequence operation. 

Programmable controllers are specific microcomputers that are designed to replace electromechanical relay logic systems. These instruments can be connected to computers for data logging or the computer may act in a supervisory capacity over the programmable controller. 

VVhile relays have a very low failure rate, relay logic should not be considered inherently fail-safe. Even if ithe relays are properly selected and applied, the contacts may weld or the spring may not return the switching contacts to the de-energized position. 

Bectromechanical relay logic systems should consider the following criteria ... 

Today sohd-state programmable controllers, which can be used in place of the more conventional relay logic in control circuits, are available. Some of these controllers are versatile and allow control logic to be changed simply. Many allow computer input-output links for record-keeping purposes. 

I have mentioned flexibility as a principal reason for success but this is when relating earlier relay logic systems with the modern computer-controlled plant. The point must be made that the logical thinking necessary to lay down the steps of sequential performance and the settings of all control parameters requires a clarity of thought and a preciseness which must have an influence on safety and reliability. 

Field input and output to the standards of security relay logic (NSlorS2)... 

The PIPC was developed to meet the market for renewals of SNCF signaling posts - to replace aging interlocking relay logic chassis, parts of which were sometimes more than 40 years old It was developed by a handful of enthusiasts between 1993 and 1999, in close collaboration with specialists from the SNCF, and was for a long time the only electronic interlocking made in France . 

Principle of the trip amplifier as an input converter to the relay logic... 

The cabinet also houses the push-button controls of numerous electrical mdors connected to pumps and blowers in the reactor s cooling system and ventilation system. Some of these motor controls are Interlocked using relay logic wtth the variables measured by channels in the cabinet, as well as with the controls in the console... 

Available technology offers a minimum of four types of safety logic systems, based on diverse logic elements, for use in reactors. The relay logic which has been tried out extensively in the safety systems of many research and power reactors has established its reliability and availability beyond doubt. However, relay logic systems are bulky. 

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