What is a level switch?

Municipal water tanks in power plants and factories must consider and control the water level.
That is why level switches and level transmitters are used to identify and measure different materials such as powders, liquids and granules in tanks and pipelines.

This type of switch is suitable for any application or product.

Therefore, these keys are used as monitoring controls, measuring devices, and alarms such as turning the device on or off.
Level switches exist in point and continuous type, the point level mainly includes optical, vertical, ultrasonic and horizontal floating and the fixed level type mainly includes ultrasonic, capacitive and floating.

Types of level switches are determined based on the type of measurement and environmental conditions

Definition of level switch: A switch that is used to determine the liquid level and the intermediate level between liquids.

Measuring liquid levels is easy.

By switching power, these switches can be used as control switches or alarm devices by turning the load on/off.

These switches are very unique because they have a solid or electromechanical latch output. and are normally closed, normal or open.

Level switch function

The way the level switch works is that the float moves as the water level rises, the output contact changes and determines the position of the water level.
For example, when a bucket is filled with water, it overflows.

Therefore, a level switch is installed at the top of the water tank to overcome this excess.

When water hits the level switch, it sends an output signal to prevent water from passing through the tank.

On the other hand, the level switch is used to prevent the tank from emptying when the water level decreases during draining.

Level switch connection diagram

The liquid level switch circuit diagram is shown below.

The circuit is designed with a few passive components, three BC107 transistors, a pair of relays and diodes.
This is a surface detection circuit designed using minimal components.

This circuit is connected according to the figure above.

In the circuit above, change the resistance R1 by placing water tanks to turn on the relay K1.

After that, disconnect the two zones from the water heater and turn off the K1 relay

During this time, the opposite party will be placed in the K2 relay.

If you can’t get the setting, replace resistor R1 with POT 500K and repeat the process.
The main problem with this circuit is probe decay when using DC.

This simple level circuit works by turning on one relay and turning off the other when the liquid level exceeds a set limit.

Whenever the liquid level probes are connected, a positive source is applied to the base terminal of transistor Q1 across the liquid.

So transistor Q1 is on. The base terminal of transistor Q2 is connected to the collector terminal of Q1 and the base terminal of transistor Q3 is connected to the collector terminal of transistor Q2.

Then transistor Q1 turns on and transistor Q2 turns off. So, relay “K2” is off and relay “K1” is on

These two relays work based on the water level.

Relay contacts like OP1 and OP2 are mainly used as control for any equipment like pumps, motors, alarms, lights, solenoid valves etc.

When the water level decreases, relay K2 and then relay k1 turn on.

Difference between level switch and level transmitter

Types of level switches

Level switches are available in different types such as ultrasonic, induction, thermal, magnetic, capacitance, potentiometric, hydrostatic, diaphragm, optical, slope, paddle, rod, conductivity, displacement, adjusting fork, potentiometric, capacitive, nuclear, rotary and paddle. have.

In the following, we examine the most common ones:

Ultrasonic level switch (Ultrasonic Level Switch)

This type of level switch is mainly used in industrial processes to detect low and high water levels.
Liquid level measurement can be done by sending ultrasonic range signals.
So by sending ultrasonic signals that work between two crystals.
Here the transmitter and receiver can be placed in a probe and somehow behind the water tank. These keys are used for solid and liquid materials.

Inductive Level Switch

An inductive switch level is simply an electronic circuit used to determine the change in inductive reactance.

To achieve this goal, the conductive fluid must cooperate with the magnetic field.

This switch is used in harsh environments due to having minimal moving parts and sealed probe.

These level switches are used in industrial applications. They can be used for conductive solids and liquids. Therefore, they can be used to communicate between conducting and non-conducting fluids.

They are non-contact level switches that simply react to the target substance as soon as the substance enters the detection field.

Thermal switch level

Thermal level switches are mainly used to detect changes in room temperature of liquids and vapors.

This switch contains a permanently heated thermistor or heated thermal resistance.

This level switch is activated when the heated temperature of the thermistor decreases.

In this type of switch, a thermistor detects the liquid level, then the liquid level can be measured with the thermistor.

The measurement by the thermistor is based on the difference in thermal conductivity of liquid and air.

Since heat dissipation is greater in liquids compared to air or gas, the resistance of the thermistor probe changes drastically after exposure to a fluid. These level switches are very accurate up to 1000 degrees Celsius.

Magnetic switch lever

This type of level switch detects the water level by measuring the level of the magnet in the float and sending the data to the control system.

This key contains energy, electricity and magnetism to measure the water level.

As it moves up, the water float descends while its float is attached to the level gauge.

Level switch calibration

Level switch calibration is essential to ensure their reliability and accuracy.

Therefore, incorrect calibration can cause errors in the results or damage the switch.

We have reviewed the steps related to pressure switch calibration below:

Fill the process up to the level change mark in the chamber.

Level switch contacts must be adjusted.

For safety, the level switch must be removed or depressurized.

Connect the pressure calibrator to the input of the level switch

Connect the device to calculate the output state of the switch.

Slowly move the fluid pressure across the operating point until the switch output changes and record the operating pressure.

Move the pressure slowly towards the return point until the switch position changes and record the return pressure.

If necessary, repeat the steps and disconnect the test equipment

Return level switch to service.

Advantages and disadvantages of level switch

Among the advantages of the level switch, the following can be mentioned:

These switches are economical so they are used to monitor, control and change the liquid level.

Each switch requires raw materials in the control manufacturing process to avoid waste.
Controlling the storage of bulk and liquid materials helps prevent waste from spills and overflows.

A properly programmed level switch can turn on a pump or valve to prevent losses and control overflow.

Costs can be saved by using these switches.

These types of switches can provide the correct data to the computer in a timely manner without activating or starting any other device.

These switches are reliable and versatile.

Installation is simple.

These switches are solid and manual.

Its design is compact.

Different types of switches are available for top, bottom and side mounting

The conductivity or dielectric constant of the liquid will not affect its performance.

Disadvantages of level switches include the following.

Moving parts are vulnerable to damage, wear and tear and jamming.

Floating excitation depends mainly on liquid contact