Controls

Instrumentation

Standard Rooms
The design objective is to maintain stringent environmental conditions, typically in an environmental room or appropriately insulated laboratory. Temperature and humidity levels must be maintained within very small deviations, drifts and fluctuations. The secondary objective is to use conventions (commercial) refrigeration equipment and operate them in an economical manner. The controls need to be flexible enough to accommodate multiple configurations and types of primary equipment.

This proven assembly of controls is capable of controlling a refrigeration system on a standalone basis, yet able of being connected on a local network for either centralized and/or remote control and monitoring.

At each room is a direct digital controller to measure space temperature (and humidity) and status of the compressors. Output relays control the evaporator fan (usually kept on except for maintenance, safety or defrost) and the liquid line solenoid valve for system on/off and low temperature safety. Actual temperature regulation is accomplished by precisely modulating a hot gas bypass valve located before the evaporator coil. The refrigerant control valve is a high performance magnetically actuated three way bypass valve. The valve resolution is 10x that of a commercial control valve and has enhanced response time and stability. Operating parameters are programmed into the controller. Whether connected or not to the network, each controller acts to maintain the set point of the connected coolers.

Sensors are selected based on measured media (temperature, humidity, pressure, etc.), accuracy requirements and the appropriate mounting is used for the site conditions.

An integral display and keypad allows the operator to make set point changes. A separate operator's terminal can be furnished as an option to digitally display and allow controller adjustments.

Most applications require a chart recorder. A 10" circular chart recorder (one or two pen) is mounted flush on the control panel. The sensor input(s) and power supply are independent of the controller.

In a network application, all of the controllers are connected, "daisy chained" to a network supervisory controller. This configuration contains all of the software features for monitoring, controlling, scheduling, alarm processing, reporting, etc. As well as the capability of dialing in and out to a remote location.

The actual computer interface to the network can either be a "dumb" terminal (VT100 emulation) or a personal computer; Either directly connected or through Ethernet. The PC can be upgraded to a full featured operator's workstation to include supervisory monitoring and control, data acquisition and graphics.