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2-8

Pre-installation Guidelines SIMATIC 545/555/575 System Manual

575 Fault Relay Operation (continued)

The time delay required for the fault relay to operate correctly is dependent

on the modules in the system. The fault relay closes within 10 seconds of

power being applied to the system if no fault is detected, and if only

SIMATIC 575 VME equipment is used in the VME base. If you use a

third-party master to log into the 575 system, the fault relay is delayed.

Third-party masters extend the time needed for a login only if they log into

the 575 system or drive SYSFAIL* for a longer time than the 575 CPUs. If a

third-party board, either master or slave, drives the SYSFAIL*, then the

fault relay does not close until the SYSFAIL* signal is de-asserted. You may

need to bypass the fault relay circuit during debug; when a system fault is

being tracked down, the fault relay does not close until the fault is removed.

Refer to Section 2.2 for more information on safety considerations.

To help place the system in a safe state for both the operator/user and the

process, you can use the 575 fault relay in conjunction with the emergency

stop switch(es) and with any interposing relays that you use for

safety-critical circuits.

NOTE: Refer to Section 2.2, “Safety Considerations,” for additional safety

information.

There are several different ways to use the 575 CPU fault relay. You can use

it to control the power to the safety-critical outputs. You can also use it to

control the power to the entire electronic control system, thereby controlling

the safety-critical outputs.

To use the fault relay to control the power to the safety-critical outputs, you

must wire the relay so that it controls the interposing relays in these

circuits. An example of this is shown in Figure 2-5.

NOTE: Figure 2-5 is not a complete electrical diagram. It is for illustration

purposes only. A qualified control engineer should be aware of any relevant

regulations and design the system with these in mind.

The fault relay can be used in conjunction with the emergency stop

switch(es) and with any interposing relays used for safety-critical circuits.

Safety-critical circuits include, but are not limited to, circuits controlling

motion of equipment and/or circuits controlling high voltage. Any circuit

that could potentially injure the operator/user if the circuit is energized at

an inappropriate time should be considered safety critical. The safety chain

permits the system to be placed into a safe state for both the operator/user

and the process.

Time Delay

Fault Relay Usage

Examples

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Siemens SIMATIC TI500 Especificaciones Pagina 43