The Importance of Liquid Level Sensors in Industrial Refrigeration Systems

teklab-liquid-level-sensors When we talk of liquid level sensors, we’re usually referring to tiny systems that are used to detect levels of liquids (like in the fuel tanks of automobiles).

These sensors are also used to detect interfaces between liquids like oil and water or between liquids and solids.

They can sense the level of liquids either continuously or at certain points following which certain alarms are triggered, like we see the red or yellow low-fuel light on the fuel gauge of a car.

Liquid level sensors that are used for continuous monitoring depend on pressure, ultrasound or vibration, or a combination of any of these methods. Sometimes, the liquids whose levels have to be sensed are corrosive, and this means that the sensors must not touch the liquids. In such cases, the sensors use ultrasonic or microwave technology.

It’s easy to relate to liquid level sensors when we’re talking about automobiles, but there’s another application of these systems that are extremely useful – in industrial refrigeration systems that are used in the fields of agriculture, fisheries, poultry and other industries.

Any refrigeration system uses pulse width modulation to control the flow rate through a solenoid expansion valve in order to compress vapor. A phase separator receives two phase refrigerant from the condenser and supplies its liquid form to the pulse width modulated solenoid valve.

This phase separator has a liquid level sensor and a controller that regulates the duty cycle of the pulse width modulated solenoid valve receives input from the sensor.

This liquid level sensor can either be the kind that sends a continuous variable signal according to the varying liquid level or it could be a switch that regulates valve duty cycle depending on whether the phase separator liquid level is above or below a certain predetermined level.

There are some refrigeration systems that also have two liquid level sensors, one of each type.

Most industrial refrigeration systems have two compressors, a condenser, two expansion devices, two evaporators, a phase separator, and a liquid level sensor.
They are connected in this order – the two compressors, the condenser, one expansion device, one evaporator, the phase separator, the next expansion device, the next evaporator, the liquid level sensor and then the controller. The liquid level sensor provides a continuously variable signal as a function of the liquid level in the second phase separator.

Some liquid level sensors used in refrigeration systems are of the capacitance bridge type that has a built-in simulation circuit for testing the apparatus, which provides improved voltage feedback damping for the stability of the circuit, and which has enhanced anti-splashing circuits that help provide stable digital displays.

This kind of advanced liquid level sensor also enables the low level adjustment set point to be set more accurately through a reversed lower differential function.

By-line:
This article is written by Kat Sanders, who regularly blogs on the topic of top online engineering degree at her blog The Engineering A Better World Blog. She welcomes your comments and questions at her email address: katsanders25@gmail.com.
Thanks Kat.

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