Unitronics PLC controllers
Versatile, compact and modular controllers at the heart of control systems across virtually every branch of industry.
Programmable controllers, thanks to their versatility, compactness, modularity and easy reprogramming, are part of the control systems in virtually all branches of industry. The task of the PLC is to execute a program that implements the control algorithm. The arguments of its functions are the states of PLC inputs, and the result of their processing — signals on the controller output. The device also communicates with other system components and carries out self-diagnostic tasks.
Unitronics PLCs can communicate over many industrial protocols such as Modbus RTU, Modbus TCP and CANopen. It is possible to communicate via serial ASCII — we can develop new protocols this way or talk to dedicated protocols. This is very useful with printers, GPS modules or devices controlled by AT commands.
I/O
The purpose of analogue PLC inputs is to convert continuous signals into digital ones, whose values can be stored in memory and processed by the processor. Typical voltage signals are −10 V…+10 V, 0…+10 V or 1…+5 V; current signals are usually 0…20 mA or 4…20 mA. They reflect changes in physical quantities — temperature, pressure, level or flow — measured by sensors monitoring the controlled process.
Analogue voltage inputs have high input impedance, on the order of MΩ; for currents the value does not exceed 500 Ω. Inputs can be differential or single-ended — the former processes the voltage difference between two inputs, while the latter uses a common ground as the reference. Differential inputs offer greater resistance to external disturbances, whereas single-ended inputs allow a higher packing density per module, though their wiring to the signal source should be shielded. Where the signal source is remote from the PLC, distributed I/O modules can be used. Configuring the Unitronics PLC I/O list is intuitive and easy — adding new modules is done by drag and drop.
Temperature measurement
Temperature input modules working with thermocouples are also popular. Like ordinary analogue modules, they first amplify the sensor signal and then convert it to digital form — but they also convert the voltage value into temperature according to the thermocouple type's characteristics. In addition, they provide cold junction compensation, simulating a constant temperature at the open end of the thermocouple and compensating for signal loss on the lead resistance. Modules working with resistive sensors perform a similar conversion based on changes in electrical resistance.
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