Infrared heaters enable the use of heating for machining and processing in manufacturing: In the glass industry, infrared heaters are used to shape glass, in medical technology for sterilization processes and in semiconductor production systems for sintering processes. Other areas of application can be found in the automotive industry for adhesive and paint drying processes (coating) and in the packaging industry in shrink tunnel systems. Infrared emitters supplement or replace the range of conventional processing options and support the development of new materials and processing methods. They are more energy-efficient than other heating technologies, as infrared rays reach the objects to be heated directly and can be directed specifically at the areas to be processed.

Monitoring and controlling heaters

The NRG control unit acts as a gateway for Ethernet, Modbus, Profinet or Ethercat communication and enables data exchange with the PLC or IPC for the switching processes as well as for the transmission of monitoring and diagnostic information. Current, voltage, frequency, power and energy consumption of the load are monitored. Diagnostic data for the solid state relays and the switched load includes information on mains loss, load loss, load deviation and overtemperature, a short circuit in the load circuit of the solid state relay and its status outside the set limit values. In addition, the number of switching operations, the operating time and the power consumption are recorded for each switching device. This allows the operating hours and power consumption of the switched heating to be recorded precisely.

The solid-state relays are a series of five different 1-pole devices. They are implemented using auto-configuration, which allows them to be set up quickly during initial integration or replacement and prevents incorrect settings. Incorrect configuration is ruled out. LEDs on the front of the modules indicate the status of the switched load, communication and alarm. The type of alarm can be identified via the flashing sequence, simplifying troubleshooting.

The solid state relays provide the data of the monitored process variables. Each individual solid-state relay in the chain can be controlled directly from the PLC/IPC, switched on or off synchronously with the mains at voltage zero crossing or precisely controlled via phase control with a resolution in 1% steps. In addition, automatic mains voltage compensation keeps the output power supplied to the load stable by adapting the control stage to the voltage fluctuations. Compensation is proportional to the setpoint specified by the main heating control system. An algorithm calculates the compensation factor on the basis of a reference voltage set by the user. A soft start function, which can be programmed either as a start-up time or with an adjustable maximum current limit, limits the very high inrush current when the cold infrared heaters are switched on.

Operating modes for power control

In addition to direct control, users can choose between pulse packet, full-wave and extended full-wave control operating modes, which can be used to specify defined control variables for each solid-state relay and therefore each heating channel in the system. The different modes reduce the load on the PLC/IPC and reduce the communication effort via the fieldbus.

The author: Michael Schultze is Marketing Manager at Carlo Gavazzi in Darmstadt.

© Carlo Gavazzi

With pulse packet control, the time base can be set in a range from 0.1 to 10 s. The control value determines the percentage of the switch-on time. With a control value of 10 %, the output is switched on for 10 % of the time base and switched off for 90 %.

Control in full-wave control is based on a control value of 0 to 100 % in 1-% steps and a fixed time base of 100 full waves (2 s at 50 Hz). This switching function distributes the switch-on cycles of the full waves as evenly as possible over the time base.

The extended full-wave control works according to the same principle as the full-wave control, but distributes half-waves evenly so that a positive half-wave is always followed by a negative one. This prevents a DC load on the supply. Its advantage over pulse packet control is that it places less strain on the heaters, as the power supply is more even and, as a result, the temperature changes are smaller.

Another operating mode is phase angle control in 1% steps.