Industrial safety specialist Castell developed a motion-monitoring product to protect workers in industries such as cement manufacturing. The BEMF unit ensures that motor-driven equipment up to 600 volts with a variable rundown time has completely stopped before access is possible.
In the cement industry, safe access to the mixer is important as set cement can easily cause blockages if not regularly washed down. However, large rotating machinery present significant dangers, even when switched off, due to the momentum built up while running. The delay between a machine being switched off and coming to a standstill can often be as long as 15 to 30 minutes.
While an electric motor is rotating, whether powered or not, it generates an electromotive force (EMF). This force is monitored by the Castell BEMF unit. When the BEMF detects zero EMF, establishing that the motor has come to a complete standstill, it releases a trapped key corresponding to a lock on the machine’s guard hatch. Access cannot be granted without the use of this key and power cannot be restored to the motor until the key is returned once maintenance is complete.
The BEMF is also designed to improve efficiency. The time wasted by fixed-delay systems is eliminated, since the BEMF ensures that machine access is granted as soon as the rundown is complete; rundown times will vary according to the load in the machine.