Our beginnings with PLCs

It is easy to see how an electrical designer gets involved with PLCs. They are cost-effective and offer a useful advantage: errors in control logic can be corrected without redrawing the circuit documentation. Naturally, designing a PLC into a switchboard also means providing its program.
The question was where to start. In 1996 I compared entry-level solutions. Specialist software companies handled the field, so we did not expect large commissions. Programming software should ideally be free and the PLC competitively priced. Schneider’s TSX nano met those criteria, and its 48 inputs and outputs were sufficient.
That remained sufficient until 2002. I then reviewed our experience and compared suppliers again. The requirements were still free development software, a free OPC server for PC integration, networking of enough PLCs and built-in PID control. My son had established Mobil-Servis, so communications capabilities also made sense. It was clear that the best offering would be
complete solutions:

• Solution design
• Detailed electrical and instrumentation design
• PLC and operator-display programming to the customer’s requirements
• PLC programming for remote control over GSM or landline networks
• SCADA programming to monitor and operate the whole process from a PC or PC network

We chose UNITRONICS from Israel. Its devices combine a PLC with an operator display (OPLC = Operating Panel + Programmable Logic Controller). They were affordable and straightforward to program. Each unit supported 64–158 I/O, with up to 64 units on CANbus and 4096 I/O in the configuration described. Models then available included M90, M91, Vision120, Vision230, Vision260, Vision280 and Vision290.
A key advantage was the complete free software supplied to use the hardware: U90 Ladder for M90/91 and VisiLogic for Vision. UniOPC connected both ranges to SCADA systems. The OPC server supported serial connections (COM1), TCP/IP or UDP/IP, and GPRS for remote PLCs.
Another advantage was reliable operation over telephone connections. RemoteAccess allowed monitoring over landline or GSM and program changes when needed. Built-in SMS functions provided reporting and control. Users could operate the PLC from a home PC as though standing in front of it. Low power consumption also made it suitable for monitoring buildings without a mains supply, using movement detectors and SMS communication around the clock.
Existing electrical maintenance staff could be trained for routine maintenance because the programming approach largely resembles the circuit diagrams they already know.