The invention relates to a safety switch and a series connection with safety switches.
Safety switches are used in the field of safety engineering; they are especially used to protect dangerous zones of machines and systems.
As an example, safety switches of that type can work with transponders; whether or not a door or the like, as access to a machine or system, is closed can be detected with the aid of the transponder signals.
A safety switch of this type typically has a redundant input structure comprised of two inputs and a redundant output structure with two outputs. The safety switch generates, in accordance with its monitoring function, especially in dependence upon the transponder signal, a switching signal that is output to a control unit via which the machine to be monitored is controlled. If a danger-free situation is detected with the safety switch, in particular that a door to be monitored is closed, a switching signal with the switching state “switched-on status” is generated in accordance with an active safety criterion, meaning a release signal. If the control unit receives this release signal from the safety switch, the control unit can start operation of the machine or leave the machine in operation. If an open door is registered with the safety switch, however, it will generate a switching signal with the switching state “switched-off status” corresponding to a safety criterion that is not active. In that case, the safety switch shuts down the machine to avoid situations that involve danger.
In general, a series connection of safety switches of that type can also be provided, in particular to monitor complex danger zones.
To reliably rule out a situation involving danger with a series connection of that type, its function is such that if a safety switch outputs a switching signal with the switching state “switched-off status”, this switching state will be passed through all of the subsequent safety switches up to the control unit, so the control unit will put the machine into the safe, meaning shutdown, state based on this switching signal.
A safety switch of that type that can be used in a series connection is the safety switch of the type CES-AR of the company Euchner GmbH & co. KG. This safety switch will be called a standard safety switch below.
A key feature of this standard safety switch is that it emits test pulses at its outputs and, in fact, both when a switching signal with the switching state “switched-on status” is emitted at the outputs and when a switching signal with the switching state “switched-off status” is emitted. These test pulses are not just used to check the switching capability of the outputs of the respective standard safety switch.