What Are Emergency Stop Relays?
An Emergency Stop Relay operates with an Emergency Stop Button to ensure that under emergency fault conditions the electrical supply to a machine/process is swiftly and reliably disconnected.
Redundancy consists of two or more relays with parallel coil circuits operated by the same control function. The contacts of these relays are connected in series to ensure that the emergency stop circuit will disconnect the supply even if one of the relays has failed.
Positive guidance exists when all the contacts of a relay/contactor are forced to operate in their correct mode during each relay operation. This is achieved by means of a mechanical drive bar which forces the contacts to behave in the desired manner. Each contact in its open position must maintain a minimum clearance between the contact faces.
Pressing the ON/Reset button to close the main circuit, will apply power to the Emergency Stop relay. A series of internal operations, checks the integrity of each parallel relay circuit with a failure on any circuit inhibiting the start operation.
Existing Harmonised European Standards require that machine mounted switches, relays and sensors incorporated in safety circuits should be used in a manner that "minimises their chance of failure to a dangerous condition." One cost effective solution is to interface the machine emergency stop pushbuttons or safety gate switches to the control system via an emergency stop relay. This relay should incorporate positive guided, cross monitored inputs and outputs. These features will significantly reduce the chance of relay failure, characteristics which are not inherent in standard control relays which often tend to fail in the closed position. Dold safety relays are manufactured to the above requirements and incorporate the following features:
Listed below are some of the standards pertaining to emergency stopping and Risk Assessment:
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