“An HMI is an operator touch panel that interfaces with a programmable logic controller (PLC) that enables users to draw graphical representations of their plant to allow them to see what is happening in their plant,” says CHI Control Components sales manager Rory Reid.
The HMi is available in four-, six-, eight- and ten-inch models and is a true analogue touch-screen operator interface with programm-able function buttons for the most robust applications.
A PLC is an industrial computer that has been preprogrammed to control specific areas of a plant. Reid explains that, in the past, the HMI was connected to a PLC which controlled what was happening in the plant by referring to the input/output (I/O) on the PLC. Now, a small PLC and an HMI can be replaced by a single new HMI, with I/O option added.
However,Reid cautions that an HMI will not be able to process the same amount of I/O as a large PLC. “Owing to a PLC’s physical structure, it can process in excess of 800 I/O points, while an HMI is limited to about 16 I/O points,” he says. “HMIs are for smaller applications. For this reason, they won’t replace PLCs completely and, because a PLC has the capability of expansion through add-on modules, the amount of expansion is limited for an HMI.”
A company would choose an HMI as opposed to a PLC when fewer I/O points are required. The HMI is used for smaller applications, where the HMI can be used as a PLC, such as a stand-alone furnace or drill press.
The HMi has been used success- fully at a paper-producing project in Durban. Each end of an individual process, called the engineering station, retrieves information from that specific engineering station. “The whole process can be tracked,” says CHI Control Components marketing director Rob Hare.
The required information is extracted from fieldbus connectivity. The Panelmate HMi from Cutler-Hammer caters for most commonly used fieldbus protocols
Other new products due to be launched include the Aucom electronic soft starter.
Soft starters limit the starting current, reducing both mechanical and electric shock to the system. Soft starters gradually increase the load by increasing the current from zero amps to 100% of the nominal current in a predetermined time. Soft starters are suited to applications such as a conveyor belt. For example, if a conveyor belt stacked with bottles was switched on, sudden acceleration of the belt would cause the bottles to fall over. With a soft starter, the start-up is gradual, allowing the belt and the contents to move together in unison.
Unusual features include a built-in bypass contractor as well as a jog function. “A jog enables a machine to be inched slowly backwards or forwards to dislodge jammed material, or feed new material into it ,” says CHI Control Components product specialist for drives and soft starters Renash Rampersadh.
The company has also introduced an 11-kV medium-voltage soft starter. The functionality of the control module on the low-voltage soft starter is available on that of the medium-voltage soft starter.
“The challenge was getting the silicone control rectifier to fit a medium voltage, when it was traditionally only used for low voltage,” concludes Hare.