Catalog relay modules - DOLD - #29

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Safety technique Restart inhibit The restart inhibit prevents a — safety-related évaluation unit from issuing an enable signal after a shutdown, change of machine operating mode or change of the actuation type. NOTE: The restart inhibit is only removed by an external command (e.g. - Reset pushbutton). Locking - Locking mechanism Locking mechanism The purpose of a locking mechanism is to maintain a — guard in its closed position. It is also connected to the control so that the machine cannot start if the guard is not closed and locked and the guard is kept closed until the risk of injury is no longer present. [DIN EN 1088] (see system overview of SAFEMASTER® STS key transfer system) Consent switch - Signal transmitter Positively driven contacts Positively driven means for contacts that no NC contact may close if any NO contact does not open. Also, no NO contact may close when an NC contact does not open. This applies to relays/contactors over the complete life cycle and also to a faulty state [DIN EN 50205]. Example: If an NO contact is welded, all the other NC contacts of the relay/contactor concerned remain open no matter whether the relay/con-tactor is energized or not. Positively opening Contact opening as a direct result of a defined motion of a switch's operat­ing element using non-sprung parts. [DIN EN 60204-1] NOTE 1: For the electrical equipment of machinery, the positively opening of NC contacts is expressly required for all safety circuits. NOTE 2: According to DIN EN 60947-5-1-k, positively opening is designated by the symbol (arrow in a circle) (function to protect persons). Two-hand circuit This is a device which requires at least an action with both hands to start and maintain the operation of a machine as long as a hazard is present. Its purpose is to protect the operating person in this way [DIN EN 574]. NOTE: In order to initiate the hazardous operation, both operating elements must be simultaneously actuated (- Discrepancy time monitoring). The enable signal is withdrawn when one of the two operating elements is re-leased during the potentially dangerous motion. The dangerous operation can only be re-initiated if both operating elements have returned to their initial position and are then actuated again. Cyclic self-monitoring - Testing Cyclic test A fault is automatically detected before or during the next request for the safety function, i.e. at each starting cycle of the — evaluation unit at the latest. 4. Safety-related switching functions The standards mendioned in chapter 2 describe main requirements for safety-related switching circuits. The following is an extract from them. 4.1 Emergency stop circuits In order to achieve a quick stop of a dangerous motion in emergency situations the reliable function of the emergency stop device is crucial. Therefore, appropriate circuits must prevent failures of devices down-stream of an emergency stop command device or a properly functioning protective device. DIN EN 60204-1 Safety of machinery Electrical equipment Actions in an emergency (emergency stop) DIN EN ISO 13850 describes the design principles for emergency stop equipment. Emergency stop and emergency switching off are complementary protec-tive measures for minimizing risks on machines (see DIN EN ISO 12100). Emergency stop is related to the actual operation of a machine, while emergency switching off is directly related to switching on/off. They are initiated by a single main action and must be maintained effective up to a manual reset action on the location where the emergency was initiated, as the control commands initiated by them. Resetting may only enable, but not execute the restarting or switching on. Emergency stop [DIN EN ISO 13850] Emergency stop must be work in compliance with the stop categories 0 or 1 depending on the carried out risk assessment for the machine. The following applies in addition to the requirements for stopping: - Priority above all other functions and operations in all operating modes - An interruption of the energy supply to machine drives that may cause a hazardous situation must occur without further risks either imme-diately (stop category 0) or in a controlled way as quick as possible (stop category 1). Emergency switching off Emergency switching off is the disconnection of the corresponding energy feed using electro-mechanical switching devices (stop category 0). If the stop category 0 is not allowed for the machine, other measures such as protection against direct touching may be required. Emergency switch-ing off should be planned when dangers or damages are possible and the protection against direct touching is only realized by distances or obstacles. Stop functions There are the following stop categories: - Stop category 0: Stopping by immediate interruption of the energy suuply (to drive ele­ments / uncontrolled stopping) - Stop category 1: Controlled stopping, the energy supply is maintained to accomplish stopping and is then interrupted. - Stop category 2: Controlled stopping, with the energy supply maintained. 4.2 Stop Stop functions of the above categories must be taken into account as a result of risk assessment and requirements for the machine. If required, facilities for connecting guards and interlocks must be pro- vided (see SAFEMASTER® STS key transfer system). A reset of the stop function must not initiate a hazardous situation. If required according to the risk assessment, stop commands must be effective for each control station. Combined start-stop controls The use of pushbuttons and similar control devices that alternatingly start or stop a motion when actuated is only allowed for functions that cannot result in dangerous situations. 31