Beginning in the early 1980s, microprocessor-based controls have been used to replace electrical-mechanical control systems on compressor and chiller packages. Traditional electromechanical components (pressure switches, rotary drum timers, temperature switches, freezestats, wiring, relays, etc.) have given way to microprocessors, EEPROMs, transducers, RTDs, analog circuits, and digital I/O modules.
The trend toward microprocessor-based systems is prevalent in both the hvac and industrial refrigeration industries.
The basic control philosophy has not changed and operates by maintaining control of a pressure or temperature relative to a setpoint; however, that is where the similarities end. Even early microprocessor-based systems had significant advantages over their electromechanical counterparts, such as:
- Operator keypad interface;
- Display of operating data; and
- Display of shutdown messages.While earlier microprocessor controllers were operationally superior to electromechanical control systems, they still had their limitations. Early microprocessor designs were proprietary and strictly limited to the oem’s equipment design.In most cases, this meant your microprocessor control system would be very limited in:
- Data editing/entry functions;
- Compressor type (screw, centrifugal, reciprocating, etc.);
- Functionality (controlling other devices);
- Analog interface;
- Diagnostic capability; and
- Custom applications (sequencing, condenser control).