Plug in memory sticks give PLC power

Tom Shelley reports on what can be done with the latest range of inverter drives with a little plug in logic The latest drives from Control Techniques can be given programmed or given PLC functionality by plugging in memory devices similar in appearance to USB memory sticks, but with rather more advanced technology. The Commander SK series, the SK standing for "Simple and Kompact" may be designed to be simple to use, but come with the means to be used for some very sophisticated applications. The ten most commonly required parameters, covering 90% of typical applications are listed on the front of the drives, and the drive auto tunes to the motor at standstill. At the same time, a 'Smart-stick' option can be inserted in the drive to save set parameters which can then be use to clone other drives or to save maintenance time if a drive needs to be changed. In addition, use of a 'Logic-Stick' with IEC61131-3 SyPT Lite ladder logic programming does away with the need for a 'nano' and 'micro' PLCs, or relays and timers, to perform sequenced operations. The software is free. Typical applications include giving a small speed kick at the end of winding each layer of yarn onto a bobbin on a spinning machine, in order to help settle the yarn between threads wound onto the previous layer. Another application is the positioning of goods on a conveyor, which requires sensing the position of successive product items, and adjusting drive speed accordingly. Despite looking like typical PC memory sticks using USB ports, the Control Techniques sticks are different. For a start, the devices do not use Flash memory but EEPROM chips. Also, they interface directly to the drive PCB via pressure pads, making use of an I2C interface originally developed by Philips for televisions. A timer I/O module with a real-time clock is also available for scheduled operations. Typical applications include filtration systems for swimming pools. An internal EMC filter is standard, meeting the requirements of EN61000-6-2, EN61800-3, IEEE C62.45 (Surge), EN61000-6-3, EN61000-6-4 and IEC61800-3. With the filter in circuit, ground leakage increases by 10 to 20mA on single phase supplies and 8mA on three supplies. If this is a problem, the filter may be disconnected by pulling out a tab on the underside. A PID controller is built in, as is a brake release function. The latter includes the ability to program in pre brake and post brake release delays. Modbus RTU (RS485) serial fieldbus communications come as standard, allowing communication with central PLCs, and laptops used for advanced drive commissioning. Baud rates are up to 38400. Optional fieldbus modules are available for Profibus DP, DeviceNet, CANopen, Interbus, and Ethernet. The first stage rollout if for drives up to 4kW. This is to go to 110kW over the next year. Control Techniques Pointers * 'Simple and Kompact' drives are designed to be simple to set up, but come with a considerable amount of sophistication. The ten most commonly required parameters, covering 90% of typical applications are listed on the front cover, and the drive auto tunes to an attached motor at standstill. * Advanced memory sticks are available to both allow cloning of drive parameters and the replacement of small PLCs * Modbus RTU (RS485) comes as standard, and optional fieldbus modules are available for Profibus DP, DeviceNet, CANopen, Interbus, and Ethernet.