Programmable relays take control of munching

Edited by the Engineeringtalk editorial team Oct 9, 2006

Programmable relays provide cost-effective and versatile control for Mono Pumps' Muncher series of high-torque macerators.

Moeller Electric easy500 programmable relays have proved a cost-effective and versatile basis for a control system that Crompton Controls has developed for Mono Pumps to use with its Muncher series of high-torque macerators.

Used in applications as diverse as protecting pumps from the ingress of solids and reducing the bulk of waste materials, the Munchers essentially comprise a series of interleaved contra-rotating cutters and spacers that provide true solids grinding.

Because of the inevitable variations in the consistency of the material fed to Munchers, however, the cutters are sometimes subject to heavy loading or even jamming.

To deal with these situations, the Muncher control system is required to monitor the power being delivered by the motor that drives the cutters continuously and, in the event of an overload or jam, to initiate corrective action.

This involves automatically putting the motor through a preprogrammed series of forward and reverse operations with the aim of restoring normal functioning.

If, after a set number of cycles, this proves impossible, the control system shuts down the Muncher and generates an alarm.

Until recently, Mono Pumps achieved these functions with a control system built around a dedicated electronics module which was designed and manufactured specifically for the application.

This approach, however, made it difficult to update or change the control sequence.

In addition, Mono Pumps wanted to switch to the use of off-the-shelf components, which would improve both lead times and availability.

After discussing its requirements with control system expert, Crompton Controls, Mono Pumps decided that Moeller Electric easy relays offered an ideal solution.

Readily available, competitively priced and exceptionally versatile, these compact devices could easily be programmed to provide all of the functions needed by the Munchers.

Further, the analogue inputs and comparator functions provided as standard by programmable relays in the easy range made monitoring the motor power particularly straightforward.

"The easy relays are very simple to program and, of course, their flexibility means that we can make changes to the control sequence easily and at little cost", said Dean Sweeney, Technical Director of Crompton Controls.

"In fact, we have discovered a very useful bonus", he continued.

"Since the program for the relays can be developed on a PC and stored on a Flash memory card, it's not even necessary to visit site to install upgrades".

"We simply send the end user a memory card with the new program, and let them plug it in themselves".

"This saves a lot of time and money for all concerned".

Moeller easy relays are now in service in the control systems of several hundred Mono Munchers, and are meeting and surpassing all requirements in terms of reliability and performance.

"They're excellent little devices", said Dean Sweeney.

"And, like all Moeller products, they're backed by superb service and support".

"We're so pleased with them that we are now using them in many other projects, wherever we need a simple, flexible and cost-effective control solution".