Control Panel – Design and component placements
it is always easier to have both schematics and component arrangement drawings completed prior manufacturing period. Electrical Control Panel components need to be placed in cabinets so that the operation of components are not affected due to electrical noise from adjacent components. Besides, heat dissipation during operation also restricts installation location for a high power electrical components such as inverter drives.
Generally, heat producing components are placed and mounted as close to the bottom as possible. Inverter drives supply power to three phase motors and also control speed and many other dynamics such as torque, load, position. Some even have connections for feedback speed sensor encoder and more advanced might have an advanced programmable electronic card that when inserted provides specific motion trajectories for motors. I have seen and worked on hundreds of inverter drives controlling motion axis and linked with each and synchronised with each other to achieve dynamic process control for continuous production lines. These are impressive technologies and when put together work with minimal maintenance work.
Installation of MCB
Power connection is usually to the bottom plate of control panel cabinet. Power connection would usually go through an isolator switch prior terminating into the mains MCB. Usually most MCBs are laid next to each other in same row of components.
MCBs not only provide protection to electrical components but also isolation so we could safely isolate one leg of electrical circuit without shutting down complete production line during shut down. MCBs are expected and good design choice whenever voltage level changes within circuit schematic. The incoming power connection is to the bottom of circuit breaker and live ‘out’ connections are the top terminals of MCB.
Relays and Contactors
Relays and contactors contains Normally Open or Normally Closed contacts which are switched when electromagnetic coils are energised with coil voltage. Coil voltage is usually 24V dc or 110 Vac but may vary based on the design of control panel. Relays and contractors exist between output of programmable logic controllers PLCs and external outputs i.e lamps, motors, inverter drives, hydraulics, pneumatic valves and so on. Relays and contractors are essential on the output of PLCs to provide isolation, protection as well as switching current as the output of PLC controller might not be strong enough to switch on a lamp directly.
A control panel design might require exciting sensors and transducers as well as amplifying sensor signals for PLC analogue channels. Sensor cables must be routed separate to all high voltage or switching signals of relays and electrical drives. Otherwise, electrical noise induced within sensor signal might dwarf measurement data significantly to be taken as reliable. Accordingly, all efforts must be made to completely isolate section within control panel for installation of instrumentation.
Programmable Logic Controllers or Programmable Automation Controllers
Programmable automation controller runs software application for machine operation. These devices acquire instrumentation data and scale these to the engineering value for sensors and transducers. For instance, a pressure transducer raw signal could be 0 to 10 V and scaling in PLC could help to display corresponding 0 to 7500 psi on human machine interface HMI display. PLC might require to do many other jobs: Application could be written to achieve safety control of production line. Decision making – when to switch on outputs to energise hydraulic valve and push flow through hydraulic power pack. Even many advanced closed loop control applications involving dynamic Proportional, Integral and Derivative PID control could be easily achieved using PLCs. I prefer to install PLCs at the top of the cabinet.
In this article, I have gone through the design of control panels and placement of some common components within enclosure.