Modern gluing or painting processes are examples of manufacturing processes that use infrared heaters, as they cannot do without targeted heating or curing using infrared emitters. However, malfunctions in an IR emitter or infrared heater usually only become apparent when the produced part does not meet the quality specifications. However, it is often difficult or costly to set up a closed control loop that permanently monitors the function of the heater. Large heating surfaces or complicated molds with a large number of small heating cartridges can only be partially monitored via a temperature sensor for cost reasons. The failure of a single heater is also often only recognized at the end result.

However, such failures in industrial heating processes can be reduced by detecting faults and malfunctions at an early stage - provided that the data from the various system components is continuously recorded and analyzed. In the case of electronic switching elements, an integrated diagnostic and monitoring system, such as the 'NRG' system from Carlo Gavazzi, is ideal for condition monitoring.
The system is based on semiconductor contactors that have been expanded to include a communication interface so that the measured values of the load and the functions of the modules can be recorded in real time and transmitted to the control system.

The modular system structure

An NRG system consists of a control unit, the NRGC, and up to 32 switching modules, the RGC1A60CM..EN, which communicate via an internal RS485 bus. The switching modules supply the data of the monitored process variables. As a gateway, the control unit establishes the connection between the modules and the PLC and enables communication. Proprietary internal bus cables carry the communication, supply and auto-configuration lines and connect the controller to the first module and this to the other modules in the bus chain; a terminating resistor is connected to the last connection.
The control unit is available with a fieldbus interface for Modbus and with an industrial Ethernet interface for Profinet IO. Both systems offer the option of controlling and switching each individual solid-state contactor in the chain via the internal bus.
The control unit for Profinet is equipped with two RJ45 ports for the Profinet interface, a cable connection for the internal bus and a 24 V (DC) power supply connection. A test button on the front allows the function of the internal bus to be checked. LEDs indicate the device status: the supply voltage at the control unit, errors in the Profinet system and Profinet bus as well as the status of the internal bus. Alarm states such as configuration errors, errors in the communication connections and internal errors are indicated by different flashing sequences. The GSD file makes it quick and easy to integrate the control unit into the Profinet world.

The solid-state contactor

The 'NRG' control unit (left) acts as a Profinet gateway for a subsystem with a maximum of 32 solid-state contactors and as a master via which each individual solid-state contactor in the chain can be controlled via the internal bus and switched on or off synchronously with the mains in voltage zero crossing.

© Carlo Gavazzi

The solid-state contactors form the switching elements and monitoring systems of the system. There are five different 1-pole solid-state contactors for a load current of 30 to 65 A (at up to 600 V(AC) load voltage). In addition to a mains connection and a connection for the heating load, they have a connection for the reference signal L1 or N for voltage measurement and two connections for the internal bus. The first solid-state contactor in the bus chain of the subsystem is connected to the control unit via one port, while the second port is used to connect the subsequent solid-state contactors. The implementation is carried out via auto-configuration, which allows quick set-up 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 so that faults such as load loss, an open load circuit due to mains failure (e.g. fuse tripped), interruption or short circuit of the thyristor can be differentiated and troubleshooting is simplified.

The function of the solid-state contactors is monitored by communication with the control unit. As the Profinet gateway of a subsystem with a maximum of 32 solid-state contactors, it collects the data of the monitored measured variables in real time via the communication interface of the solid-state contactors and transmits them to the PLC. Current, voltage, frequency, power, energy consumption of the load and operating hours are monitored. Information on mains loss, load loss, load deviation and excess temperature, a short circuit in the load circuit of the solid-state contactor and its status outside the set limit values are available as diagnostic data for the solid-state contactors and the switched load. The number of switching operations, the operating time and the power consumption are also recorded for each switching device. This allows the operating hours and power consumption of the switched heating to be recorded precisely.

Control via Profinet

Michael Schultze is Marketing Manager at Carlo Gavazzi in Darmstadt.

© Carlo Gavazzi

Monitoring alone is not enough for heating applications. In order to reduce waste by optimizing the control process, solid-state contactors must also be precisely controllable. Using Profinet, each individual solid-state contactor in the chain can be controlled via the internal bus using the controller as master and switched on or off synchronously with the mains at zero voltage. In addition to direct control, users can choose between other operating modes with which they can specify defined control variables for each solid-state contactor and therefore each heating channel in the system. The operating modes reduce the load on the PLC and reduce the communication effort via Profinet. In On/Off mode at the control unit level, for example, the switching function of all RGC1A60CM..EN modules in the chain is controlled individually directly by the PLC.

The other operating modes - pulse packet control, full-wave control and extended full-wave control - enable targeted power control of the load. With pulse packet control, the time base can be set within a range of 0.1 to 10 seconds. The control value determines the percentage of the duty cycle. 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 one-percent increments 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
This prevents a DC load on the supply. The advantage of evenly distributed pulses and extended full-wave control over pulse packet control is the lower load on the heaters, as the power supply is more even and, as a result, the temperature changes are smaller. In addition, the visual flickering of infrared radiators is much less pronounced with extended full waves than with evenly distributed full waves or even pulse packet control.