Microwave heating cavities and applicators - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 207

To p Radiator Cap

Sight Glass

Te mperature and
Pressure Sensors

External Water
Supply Output

Water-to-Water
Heat Exchanger

External Water
Supply Input

Figure 6.13 The external cooling loop comprising heat exchanger, cooling tower, and
external pump.

according to input of the user and safety and health requirements. The vari-
ous components of a typical control unit are briefly explained next.

6.2.4.1 Programmable logic control
The PLC is the heart of the control unit. A PLC is usually used to control
the internal units of the microwave heating system and to communicate
with external computers, processors, and Ethernet/Internet Protocol (IP)
networks. The PLC includes three main modules: I/O (input/output) mod-
ule, processor, and communication module. The I/O module is used to send
and receive commands to and from the sensors and controllers. The output
and input information, from the operator or the sensors, is processed within
the processor unit according to the logic control program encoded in a pro-
gramming language compatible with the PLC. The PLC communication
module comprises Ethernet/IP and modem modules to communicate with
the external computer and processors. The communication module can be
used to change and modify logic programming and monitor the proces-
sor operation remotely. The various components of a PLC used to control
a typical industrial microwave heating system are shown in Figure 6.14.
PLCs are usually connected to a viewing panel through a local control
module. The panel is used to receive the operator's input commands and
show the system status prior to and during microwave generation.

6.2.4.2 Sensors and relays
Sensors and relays are used to monitor the operation of the various parts of
the microwave heating system. A relay is an electronic switch that can stop