Safety
Presence Sensing Devices
Light Curtains
Notes for use with Sample Application Circuits
NOTE 1
In the following circuits the type of Guardmaster device is shown as an example to illustrate the circuit principle. For specific applications the choice of Guardmaster device type should be based on the suitability of its characteristics for its intended use.
NOTE 2
In most of the following examples showing dual channel applications, one interlock switch is shown switching both channels (one contact set per channel). If it is foreseeable that damage to the guard (e.g., at the actuator mounting point) could allow it to be opened without operating the switch then two separate switches may be required. The electrical principle of the circuit will remain the same as shown.
NOTE 3
In most cases the circuits are shown with the guard door closed and ready for motor starting by operating the normal start control.
It must be possible to start the machine only by voluntary actu-ation of the control provided for the purpose (see EN 292-2: 3.7.2). For the purposes of these examples the use of a con-ventional contactor latching circuit has been assumed. If this is not the case, then a restart interlock will be required to prevent an automatic or unintended starting of the motor when the guard is closed. A Guardmaster Minotaur with a momentary action push button installed in the X1-X2 output monitoring circuit can be used to achieve this.
If the guard is designated as a Control Guard (see EN 292-2: 4.2.2.5) these requirements do not apply but the use of control guards is only allowed under certain conditions including:
- A control guard can only be used where there is no possibility of an operator or part of his body staying in or reaching into the danger zone while the guard is closed.
- The control guard must be the only access to the hazard area.
- The interlocking system must have the highest possible reliability. It is often advisable to use a solenoid locking switch such as the Guardmaster Atlas or TLS-GD2.
NOTE 4
Safety monitoring relay units used in dual channel circuits with infrequent operation or with more than one switching device connected. This note applies to all monitoring devices which use the technique of comparing the signal at the change of state of dual channels.
Certain faults are only detected at a change of state of the input switching device (interlock switch or E-Stop switch). If there are long periods (e.g. months as opposed to days) between switching actions, it may be possible for multiple faults to accumulate which could lead to a dangerous situation. There-fore a regular check should be perfomed on the system in order to detect single faults before an accumulation occurs. This check may be manual or initiated by part of the machines control system.
If, for example, 3 interlock switches are connected to the monitoring unit, certain faults will only be detected at the switch on the first guard to be opened and the switch on the last guard to be closed. This is because any switching between the first opening/last closing will not change the state of the monitoring unit input circuits. Therefore in some applications it may be necessary to use one monitoring device per switch.
Most of the following examples show an interlock switch and an emergency stop switch combined in the circuit. When a monitoring safety relay (e.g. Guardmaster Minotaur) is used for fault detection it is important to note the following:
- All safety critical single faults, except for certain faults over the contact sets at the E-Stop, will be detected at the next opening of the guard.
- All safety critical single faults, except for certain faults over the contact sets at the interlock switch, will be detected at the next operation of the E-Stop.
- Because the E-Stop device is not likely to be operated frequently, it is recommended that its function is checked (with the guard closed) on a regular basis (start of shift or daily) to enable the Minotaur to detect single faults. If the guard is rarely opened, the interlock switch should be checked in a similar manner.
NOTE 5
This symbol indicates that the associated component or device features direct opening (positive opening) operation. In the event of a fault, welded contacts will be forced open by the motion of the safety guard.
This symbol denotes mechanically linked contacts; if one contact welds closed, all other dependent (auxiliary) contacts remain in position, i.e. they cannot change state.