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Safety relays

Transistor relays may also be used in coimection with contact manometers (< /. chap. 8.3.1 and 8.3.1.1). They are commercially available as a combination of standing or supported device. They operate on the normally open and normally closed principles where a circuit is switched on and off, respectively, on making a contact. These relays are further employed for photoelectric circuits, e.g. in the level control of liquids and in vacuum control (c/. chap, 8.6 and 8.3.1.1). As safety relays thev switch off the circuit if the contact thermometer fails. [Pg.446]

Liquid-immersed transformers are fitted with special safety relays and devices to safeguard the unit from internal faults and explosions. Slowly generated faults tend to produce gas from the oil or liquid. [Pg.139]

These designs had predictable failure modes and provided good space density and weight compared to safety relays. But like safety relays, these systems required careful design procedures to reduce the chance of an implementation error. These systems could be hard to maintain especially in a situation where logic changes were necessary. [Pg.146]

Software-based parameterization of safety-related parameters shall be considered as a safety-related aspect ofSRECS design that is described in the software SRS. Parameterization shall be carried out using a dedicated tool provided by the supplier of the SRECS subsystem(s) e.g., analog sensors, intelligent safety relays, etc. [Pg.183]

As shown in Figure 2, there is a safety chain composed of safety relays in serial that activates the pitch control safety function whenever the chain is opened. The pitch control safety function leads the wind turbine to a safe state protects the mechanical integrity of the wind turbine by moving the blades to anti-aerodynamic position. The safety protection function must ensure that design limits of the wind turbine are not exceeded (e.g., over speed) and if exceeded output safety relays connected to the safety chain must be opened. The safety protection and pitch control functions must meet PLd level of ISO-13849 [18] and IEC-61508 SIL2/3. Table 1 shows most relevant safety requirements to be met by this simplified example safety concept [32,33]. [Pg.7]

SRAVT.r The safe state is the de-energization of output safety relay(s) ... [Pg.8]

SR.WT.8 Output safety relay(s) is(/are) connected in serial within the safety chain... [Pg.8]

The safety node (SCPU) has a Hardware Fault Tolerance of one (HFT = 1) based on two independent processors. Each processor controls one independent safety relay that can be de-activated (safe state) either directly commanded by safety protection or indirectly by diagnosis function. If the diagnosis detects a fatal error, it does not refresh the associated watchdog and this leads to a reset of the node. As a summary ... [Pg.8]

Each processor controls one independent safety relay... [Pg.8]

Safety Protection partitions control associated safety relays (command digital output and confirm state with digital input) and performs reciprocal comparison of results by software... [Pg.12]

Under the Mediterranean LGV project, preliminaiy studies have shown the benefits of integrating interlocking and signaling functions into a single safety computer in order to significantly rednce the nnmber of safety relays necessary to set up a signaling terminal. [Pg.76]

Past experience and feedback on electro-mechanical safety relays confirm this reasoning a relay that remains in a raised position, despite an interruption of power, occurring, on average, several billion times more often than not. And it is man, in this case a maintenance agent, who preventively or remediaUy forces the automation, constituted by a signaling installation, to stay within its area of operation. [Pg.118]

Any failrrre (master/slave syrrchrony not respected, or the erroneous signature of a self-test or erroneous control of a gate), even fleeting, resirlts in stopping the activation of the watchdog (safety relay), an irreversible fallback of the sub-systems... [Pg.133]

Beyond the detection of a latent failiue, there must be a sanction whose performance must be based on simple concepts (and therefore easily demonstrable). The sanction can be viewed in two stages immediate safety (instantaneous behavior of the architecture) and secmely maintaining the fallback position. Immediate safety limits the spread of crash scenarios. This action can be ensinod by probabilistic safety , as is the detection of the failme. In contrast, the maintenance in a secure condition can only be guaranteed by the principles of intrinsic safety. The PIPC cuts off the output power supply with an intrinsic safety watchdog mechanism, based on safety relays (using gravity). [Pg.157]

The watchdog cards of each unit determine an external watchdog based on intrinsic safety relays (using gravity). The relay contacts on the watchdog card are placed in series with those of the watchdog of the dual unit, in order to operate the safety relay that disconnects all internal power supply and especially towards the external safety interfaces (relay signaling). [Pg.161]

Electronic modules called electronic safety relay subsequently appeared, implementing predefined-type schematics, which are easier to wire, and integrating summary diagnosis. These modirles are widely used in the manufacturing sector for the management of emergency stop, zone control by immaterial barriers, or for the... [Pg.379]

The traditional safety functions are typically performed by electro-mechanical components, while the programmable electronic systems are suitable for more complex fimctions. Thus the combinatorial logic is integrated on an electronic card that is commonly called safety relay . [Pg.388]

Typical safety relay arrangementfor an emergency stop function... [Pg.143]

Figure 5.6 shows a typical application to an emergency stop function. The monitoring relay assembly will not reset if any of the relays is not in its correct state at the time of start up. The integrity of the safety relay depends on the principle of positively guided contacts. This requires that the contact sets in the relay be directly and rigidly linked to each other. Then it becomes almost certain that the state of one pair of contacts will always define the state of the other contacts. [Pg.143]

Safety relay modules can be of value in process safety systems because of their high integrity and redundant characteristics. They may be used as input stage devices but will be expensive to use for the logic functions. The self-test on start up is of limited value in low demand applications where reset may only take place once a year. [Pg.143]


See other pages where Safety relays is mentioned: [Pg.438]    [Pg.145]    [Pg.146]    [Pg.880]    [Pg.228]    [Pg.235]    [Pg.236]    [Pg.236]    [Pg.237]    [Pg.75]    [Pg.134]    [Pg.143]    [Pg.143]   
See also in sourсe #XX -- [ Pg.145 ]




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