Level sensors can also be implemented for use as a level switch. There is a difference in application between a level sensor and a continuous level measurement sensor.
Level switches are are designed to send a signal output or energize a dry contact/ or relay when the level of a solid or liquid in a tank reaches a certain amount. Some switches are designed to only activate when a tank is “too full” or “too empty” or possibly even both. A level sensor does not necessarily have to maintain high accuracy over the range of measurement but must be good enough to activate a switch which controls a pump, electrical supply to other circuits or activate an alarm which could be audible or visual. A switch can provide low or high level alarm. Previously it was popular to feed the switch contact to an alarm annunciator but these days the PLC is more popular because of the ability to implement one’s own logic for the process.
Types of
This is a very broad subject but basically there are so many types of level sensor available these days that it is not impossible to cover any kind of application one might encounter. It is important to take a look at a system design to determine what kind of material is being measured and whether or not the contact for the level sensor should be open or closed in an alarm condition.
The names given to the level sensor denote the sensor type being used whether it is electrical, mechanical or using some frequency or wavelength within the known electromagnetic spectrum. A mechanical device or pressure sensor can act as a level sensor but there are many other choices which use inductance, capacitance, radar, ultrasonic and even light. Of course, manufacturers can select the most appropriate technology for the particular tanks, silos or storage bins they are using. Switches are often used as level control and are at the heart of pump control e.g to prevent overspill, a level sensor can turn off a pump.
Here is a short list just naming a few types. However, it is not always a hard a fast rule that a certain type is implemented. There are overlaps in their applications and often the decision on which type to use might fall into the hands of the user i.e. user preference or the technical consultant’s recommendation.
Utilizes a flexible diaphragm that moves in response to pressure changes caused by the level of material in the tank.
Detects level changes by measuring variations in capacitance caused by the presence or absence of material.
Works on the principle of electrical conductivity, suitable for liquids that conduct electricity.
Operates using a buoyant displacer suspended on a spring, which moves in response to the liquid level.
Uses inductive sensing to detect metallic materials, ideal for certain types of bulk solids.
Contains a tuning fork that vibrates at a certain frequency. When the fork is covered by material, the vibration frequency changes, triggering the switch.
Uses light to detect the level of clear or colored liquids.
Employs radar or laser technology to measure the distance to the material’s surface, ideal for applications requiring non-contact measurement.
Features a rotating paddle that stops when it comes into contact with material, indicating a level change.
Measures the pressure exerted by the material to determine its level.
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