Explanations of Safety Terminology

Supervised Reset

The input must both be closed and opened before the outputs of the safety relay are activated. Using this method both the reset device and the interconnecting cable are supervised.

Bypass Connection

This is sometimes permissible where it is required to, e.g. allow material transport into a dangerous area. The Bypass Connection must be of the same safety level as the safety device being bypassed.

Test

The input is used to supervise contactors and valves, and must be closed before the safety relay can be reset. It can also be used as a simple form of reset only requiring a contact closure. In this case however, the risk of short circuit must be prevented and the reset device supervised separately.

Time Bypass Connection

This is the provision of a guaranteed maximum time for the transportation of material or passing with an enabling device.

Time Reset

This is used to prevent unintentional reset when somebody is in the risk area. Within a guaranteed maximum time two or more reset push buttons must be activated. The PB's must be placed in such physical positions so that the users can overview the total danger area. The Time Reset function can be achieved using a JSHT1 in combination with a safety relay incorporating a supervised reset.

Inching

Inching requires safety outputs to be closed for a maximum period of time allowing the machine to move only a short distance each time the inching control is activated. The time must be designed so that the specified time will not increase in the case of component failure.

Delayed Safety Stop

Where it is permissible to allow a machine to stop before disconnection of power, it is necessary to achieve a Delayed Safety Stop. The delay period being the time between the initiation of the stop signal and the opening of the safety contacts. The time delay must be designed in such a way that it will not increase in time in the case of a component failure. This type of delay is permitted, dependent upon risk assessment, for both emergency stops and other safety devices.

Three-Position Enabling/Hold to Run Device

These devices are used during troubleshooting or testing of machines. If the device push button is pressed into its bottom position or released completely a safe duplicated stop signal is given. Jokab Safety's Three-Position Devices have duplicated switches and are supervised by a true two input channel safety relay.

Contact Strip/Mat

Contact Strips/Mats can be supervised by a true two input channel safety relay. A stop signal being generated when both inputs are connected (short circuited) to each other.

Foot Pedal

Safety relays can be used to supervise Foot Pedals to ensure correct operation and to ensure short circuits in connecting cables do not cause unintentional start signals.

Brake Strip

When a Brake Strip is squeezed the contacts within the strip are forced open and provides a stop signal via a suitable safety relay.

Emergency Stop

When an Emergency Stop push button is activated a stop signal is given via a safety relay. Reset of the Emergency Stop device should not by itself lead to a start signal being given.

Two-Hand Control

This requires the use of a safety relay to supervise that the two start push buttons are pressed within 0.5 seconds of each other before a start signal is allowed. The highest safety level requires two contacts in each PB, a duplicated stop function being given even if only one PB is released (see JSBR4). Short circuits between connecting wires are detected automatically. In the lower safety level other safety relays can be used.

Machine I/O

All types of machines have a need to interface to emergency stops, contactors and other types of safety devices. Approved safety relays make this easy to perform.

Interlocked Hatch

When an Interlocked Hatch is opened an interlock device gives a stop signal via a safety relay. If the hatch cannot be entered by a human body automatic reset can be allowed.

True Two Channel

True Two Channel requires two inputs with different voltages to be closed before the safety relay can be activated. A stop signal is given even if only one input is opened or a short circuit is detected across the inputs.

Interlocked Gate

When an Interlocked Gate is opened an interlock device gives a stop signal via a safety relay. If the gate can be passed by a human body a safety relay with a supervised reset should be used.