Use of Pulse Width Modulated Valves in Industrial Refrigerat
Use of Pulse Width Modulated Valves in Industrial Refrigeration (1997)-In recent years, electronic controllers have been introduced to the industrial refrigeration market. As a result, new control devices have been developed such as the pulse width modulated valve. The pulse width modulated valve is a digital alternative to analog types of modulated valves, like motorized and temperature actuated valves. This paper discusses the basic principle of pulse width modulation and presents two applications where pulse width modulated valves have been used. The first application involves the control of liquid level in a pump recirculation accumulator where a capacitance rod is used as a liquid level measuring device. The signal from the capacitance rod is processed in an electronic controller that continually signals a pulse width modulated injection valve. The second application involves the automatic control of refrigerant injection into an air unit on a liquid overfeed pump recirculation system. A heated temperature sensor on the air cooler, an air temperature sensor and a pressure transmitter are used as inputs to a newly developed electronic controller. The controller continually manages the modulation of the pulse width modulated valve that injects refrigerant into the air unit. This controller is an alternative to fixed injection, which is traditionally used on such applications.
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