Product category:
Machine Safety Monitoring and Control
News Release from: Castell Safety International | Subject: BEMF
Edited by the Engineeringtalk Editorial
Team on 03 April 2003
Motion monitor checks for safe stopping
Castell has designed an innovative motion-monitoring product for use with trapped-key access control systems.
Castell has designed an innovative motion-monitoring product for use with trapped-key access control systems The BEMF unit ensures that motor-driven equipment with a variable run-down time - typically mixers, hammer mills and pellet mills - has completely stopped before access is possible
This article was originally published on Engineeringtalk on 11 Dec 2002 at 8.00am (UK)
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This avoids reliance on a fixed time delay, which can overcompensate run-down times for lighter loads.
While an electric motor is rotating, whether powered or not, it generates an electromotive force (EMF).
This is monitored by the BEMF unit.
When the BEMF detects zero EMF, and thereby establishes that the motor has come to a complete standstill, it releases a trapped key corresponding to a lock on the machine's guard hatch.
This key can then be used to gain access to the machine.
The BEMF eliminates the time wasted by fixed-delay systems, since it ensures that machine access is permitted as soon as the run-down is complete; run-down times will vary according to the load in the machine.
The BEMF unit can be connected to both AC and DC motors, as well as motors with DC braking systems and variable-speed drives.
It has been designed to provide the highest level of safety when installed as part of an access control system for dangerous machinery, and is suitable for category 4 safety applications.
In contrast to movement-sensing devices, whose proximity sensors need to be positioned adjacent to a motor's moving parts, installation of the BEMF is facilitated by the fact that it can be situated at the motor's control panel.
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