BEMF monitors mixers to protect workers in cement industry
Castell has developed a motion-monitoring product to protect workers in industries such as cement manufacturing. The BEMF unit ensures that motor-driven equipment up to 600V 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 presents significant dangers, even when switched off, due to the momentum it builds up while running.
The delay between a machine being switched off and actually coming to a standstill can often be as long as 15-30 minutes. This interval is the most dangerous time for a machine because, although the machine is off, it is far from being safe. Access to the machine should be prevented until it has come to a complete stop.
In addition, workers gaining full-body access to rotating machinery could have a door shut behind them. The individual is then trapped inside a machine which, due to a switch on the door becoming activated, could be restarted, often with tragic results.
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.