Speed monitoring for hazardous unsafe machine

Situation sketch

In this scenario, the placement of an object is only permitted when the machine is completely stopped. As long as the machine is operating at normal speed, the security lock is locked and access to the hazardous area is not permitted. Access to the hazardous zone is only possible once the machine has completed the work cycle or when the user switches the mode selection switch to "request for access" during the cycle. The machine carries out the remaining work, switches to a standstill and the request for access can be accepted. As soon as the machine has stopped, the door to the machine is unlocked and the door can be opened. In this case, the speed monitoring relay checks whether the machine has actually stopped (speed zero). Read more about speed monitoring with relays and other modules.


For maintenance it is necessary that the machine works at a reduced speed or is stationary. The user will have to switch the mode selection to the "maintenance" position. When the machine stops and the lock (safelock) is unlocked, access to the machine is possible. If it is desired that the machine continues to run while the maintenance worker is in the hazardous area, the use of the Grip switch is possible. The speed monitoring relay detects whether the speed of the machine is below a defined threshold value. The speed is defined in the Mosaic (MSD) programmable safety relay. If the threshold value is exceeded or the handle switch is released, the machine is stopped immediately.


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Speed monitoring relay for hazardous machine - ReeR Safety
Safelock - Safety switch - ReeR Safety

Safety components in the application example

Security lock / Safelock

The door to the dangerous application is protected with a safelock. The safelock from ReeR Safety can only be operated via the mode selection panel. As soon as the application is secure, access to the machine is released.

Reset button

If the emergency off button is activated, the machine or hazardous installation stops immediately. To resume the machine, the control panel is equipped with a reset button. If the safelock is closed correctly, the installation can be restarted.

Emergency stop buttons

The last safety component are the 4 emergency-off buttons from steute present in this application example. The emergency stop / emergency stop buttons are present in the technical installation as extra safety or as a last stop. If an emergency stop in a technical installation is desired, this can be activated by using the emergency stop button.


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Solution with programmable safety relay - Safety PLC

Classic safety components

To build the safety circuit with traditional safety components, a minimum of 6 safety modules should be used, which must be connected to each other to perform the required functions. 2 safety relays for the light screens, 3 relays for the slide switches and 1 relay for the emergency stop buttons.

Solution with safety system - Mosaic

When using the Mosaic programmable safety relay from ReeR, the following modules are sufficient to install the safety circuit:

Explanation: Using the Mosaic programmable relay, all safety circuits are implemented using a graphical interface and not by wiring all outputs of the individual safety relays. The correct functioning of the design is checked by the validation function and tested with the simulation and monitoring function. Safety functions can easily be added or removed during the design phase, for example by adding other sensors or switches. Tests during start-up can be performed to prevent the safety system from being circumvented, something that is always possible with traditional relay modules.


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Speed ​​monitoring for dangerous machines and installations

More application examples

Read more about application examples for machine safety with safety PLCs and safety switches. 

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