Appliances like toasters, microwaves, dryers, dishwashers, hot water kettles, sandwich presses, air fryers, just to name a few. 

Another very crucial appliance is the Washing Machine. 

Whether you have one at home, or use one at your local dry cleaners, this appliance is an amazing piece of engineering that makes our lives so much easier.

Without a washing machine you would have to physically wash your clothes by hand (which isn’t very fun!).

Sensors play a vital role in many different parts of a washing machine to help it achieve the task of washing clothes and fabrics. 

Below are some of the sensors used in a washing machine;

• Temperature
• Rotor position
• Dirt
• Water level
• Optical
• Vibration

This article shall take a closer look at the different parts of a washing machine, types of sensor used, and why these sensors are essential in the overall functionality of the washing machine.  

Deeper look at sensors and washing machines

Before we dive into what sensors are used in washing machines, it will help to learn a bit more about the sensor and washing machine individually.

This will help you later understand why certain sensors are used for certain parts of a washing machine. 

But, if you aren’t too concerned with learning about sensors or washing machines, you can always skip straight to the section ‘What sensors are used in a washing machine’ further down. 

What is a sensor

Embedded systems (such as a computer)  in the most simplest form consist of inputs, a processor and outputs.

Let’s consider a computer. It has inputs (mouse, keyboard), a processor (Central Processing Unit), and outputs (printer, speakers, monitor).

So what is a sensor? 

A sensor is a type of input device whose main function is to ‘sense’ physical changes in the environment (real world) and provide this information to the processor of the system. 

Us humans have our own sensors. 

Five of them!

We have the ability to make sense of the environment around us through Touch, Smell, Sight, Taste and Sound. 

Just like a computing system, we too also have a processor (our brain), and outputs (muscles, arms, legs).

So, imagine you are at a party and the DJ plays your favourite song.

You are able to sense the sound waves traversing the airwaves using one of those five senses (in this case sound through your ears).

This information is sent to your brain (processor) which realises this is your favourite song! It then informs your body(output) to move uncontrollably (or controllably depending on your dancing skills) to the beat of the song. 

Sensors in computing and electronic systems work in the same manner. They provide information from the world to the processor who can deal with that information as needed. 

For example, let’s take a look at a fan heater. 

This fan heater will have a temperature sensor which has the job to sense the ambient temperatures to ensure that the temperature you set is maintained. 

If temperatures start to rise, the sensor will sense this rise, and then relay this information to the processor. The processor can then suspend heating until temperatures fall back to the levels you set. 

Why we use sensors

But, are sensors really that essential? 

The simple answer is yes! 

There are many benefits to using sensors in embedded systems. 

Let’s go back to the heater. If it did not have a sensor, the temperature would rise above the level you set making the room hotter than you would like. 

Sensors provide a means of feedback of real world data so that changes can be made by the processor if needed.

Other advantages include;

• Making systems more efficient
• Predictive and preventative maintenance
• Increasing accuracy 

Closer look at the washing machine

Let’s take a look at the washing machine. 

Whether you have used one or not, you would have no doubt come across a washing machine before. 

The main purpose of a washing machine is to wash different types of fabrics and clothing. It was created to make our lives easier by eliminating the manual labour needed for washing clothes with your hands (i.e, rubbing clothes together and squeezing water out of them).

The only manual labour associated with washing your clothes with a washing machine is loading the clothes into it.

Different types of washing machine

There are primarily two types of washing machine, which can be classed by how clothes are loaded into them; Top loading and Front Loading.

Top loading washing machines

This type of washing machine has its opening for the clothes at the top where clothes are loaded from. 

A great advantage of this type of washing machine is that you do not have to be constantly bent over while loading and unloading clothes.

Front loading washing machines

This type of washing machine has its opening for the clothes in the front where clothes are loaded from. 

According to studies this type of washing machine consumes less power, while giving the best washing results.

Different parts of a washing machine

Rather than having one part that performs all of the functionalities, the washing machine consists of many different parts each having a specific task that helps the washing machine achieve its ability of washing clothes and fabrics.

Taking a closer look and understanding the different parts will be of help later as to why particular sensors are used in the washing machine. 

While there are front and top loading versions, the parts that I am going to cover will be found in most washing machines. 

Let’s take a look. 

Part #1 of a washing machine: Washing machine tub

The bulk of a washing machine is the Washing Machine Tub. It usually consists of two parts; an inner tub and an outer tub.

In top load washing machines, the inner tub is commonly referred to as a wash basket, and in front load variations it is known as a drum.

The outer tub remains in a fixed position and has the job of holding the inner tub as well as collecting wash water so it can be drained. 

The inner tub is where you put all your clothes or fabrics and rotates back and forth in order to clean them. It can be made with various materials that include plastic, porcelain and stainless.

Part #2 of a washing machine: Agitator/Impeller and Lifter/Fins

We just saw that the inner tub is where you put all your clothes in and rotates back and forth to clean them. However, just rotating isn’t going to help much to remove stubborn dirt and grime.

In top loading washing machines, an Agitator or Impeller sits in the middle of the inner tub and aids in the cleaning of clothes. 

In front loading versions they are known as Lifters or Fins which help the tumbling and mixing of clothes inside the inner tub. 

Part #3 of a washing machine: Motor

The rotation and movement of the inner tub doesn’t happen by magic. It harnesses the awesome powers of a motor to do so.

In front load models, the motor sits at the bottom, whereas in top load versions it will reside in the back.

The motor can either be a direct drive, or a belt drive. 

Direct drive motors are connected directly to the inner tub, whilst belt drive motors are connected to the inner tub via a belt. 

Part #4 of a washing machine: Water inlet valve

The washing machine needs water to rinse and clean the clothes. 

It gets this water by using what is known as a water inlet valve. It consists of two ports, one for hot water and one for cold. 

However, sometimes water inlet valves will only have one port for cold water. These types have an internal heater to heat the water to the right temperature. 

Part #5 of a washing machine: Drain pump

Washing machines go through different cycles to wash clothes which include a main wash, first rinse, and final spin.

As you can imagine, the water after the first main wash is going to be very dirty. Using this same water during the different cycles to clean your clothes isn’t very hygienic. 

This is where the drain pump comes in.

It has the job of removing water before, during and after different wash cycles. 

Part #6 of a washing machine: Washer drain hose

As we just saw, the drain pump removes water from the inner tub. But, it needs somewhere to go. 

A drain hose is connected to the drain pump and provides a means for the water to travel through. It usually exits the washing machine from the bottom or the back and ends up in a sink where the water can be drained.  

Part #7 of a washing machine: Console and display

The console is the main interface which you use to interact with the washing machine and select the different settings such as cycles, timing, temperatures, fabrics, etc. 

What sensors are used in a washing machine

Like most electrical and electronic devices, machines, etc, washing machines will have gone through the evolution process and had changes from their initial versions.

However, their overall functionalities stay very similar (as we saw with the different parts of a washing machine). 

When it comes to Sensors, one washing machine might have more compared to another, however, there are a set of sensors that are common in every washing machine. 

Below are commonly used sensors in a washing machine. 

Sensor #1 used in a washing machine: Temperature

The first sensor that you would find in a washing machine is a Temperature sensor.

There are many different types of temperature sensors, each using different forms of technology and working principles to measure the temperature of air, liquid or solid objects. 

Common types include;

• Thermistor
• Resistance temperature detectors (RTD’s)
• Thermocouples

So, why are temperature sensors used in washing machines?

A washing machine isn’t just used to wash one particular type of garment or fabric. Because of this, it offers a range of temperatures for different fabrics to ensure they do not get damaged when washed. Also, during the different periods of a wash cycle, a range of temperatures are used.

Temperature sensors are used to measure the temperature of the water, relay this information to the water inlet valve to help regulate the flow of hot or cold water to maintain the desired water temperature. 

As well as measuring the temperature of water, temperature sensors are used to measure the temperature of the motor to make sure it does not overheat (which has the potential of damaging it).

Sensor #2 used in a washing machine: Hall-effect / Reed sensor

Next up are Hall-effect sensors  and Reed sensors. 

A hall-effect sensor is a class of sensor that has the ability to detect the presence and magnitude of a magnetic field. 

Not traditionally a sensor, a reed sensor is a type of switch that opens (or closes) in the presence of a magnetic field. While they can detect the presence of a magnetic field, they cannot measure the magnitude. 

Both of these devices are very versatile and have many different uses in washing machines. Let’s take a look at some. 

Measuring motor speed

As we saw earlier, the inner tub is the part of the washing machine that rotates with the help of a motor.There are many different wash cycles each having their own speed of rotation of the inner tub. 

Hall-effect sensors are used in washing machines to detect the speed of the motor to ensure the inner tub is at the right speed for the right wash cycle. 

The hall effect sensor also has one added benefit of being able to detect the direction of rotation of the motor.

Lid/Door position

As a safety measure, washing machines do not begin any cycle if the lid/door is open, as water could spill out. 

It will only commence a wash cycle if it is closed.

Reed sensors are used to detect when the door is open or closed. They are contactless giving them a greater lifespan. 

Water level

Water is constantly being pumped in and out of a washing machine for the many different wash cycles that it goes through (as different wash cycles may require different amounts of water).

But, just randomly pumping water in or removing it is not an effective method, as you might add or remove too much causing incorrect levels of water.

A crucial component is knowing the current level of water so that the right amount of water can be pumped in or out. 

While there are many methods to measure water levels, one very common one is using a reed float sensor, which comprises two parts; a reed switch housed within a shaft, and a magnet inside a float. 

The float sits in the water and moves up and down with varying water levels. The reed switch within the housed unit closes whenever the float comes within close proximity.  

Dial position

You might just be washing a small load, or require low temperatures, or high soak levels, etc. A washing machine has many different features and functions for different fabric types.

The console is where a user interacts with the washing machine to select the right settings.

While earlier models had less features and used buttons, newer models have many more features and utilize a rotation dial.

Earlier, washing machines used mechanical selector switches for the rotation dial. However, mechanical switches wear out fast.

A better option for a rotation dial is a Rotary Hall-effect sensor which has no moving parts giving it a longer lifespan.

Vibration

Last up for hall-effect and reed sensors, is detecting vibrations in a washing machine. 

You might have witnessed it for yourself, and seen that washing machines can get quite violent and vibrate at alarming rates.

These vibrations can cause damage to the motor’s bearings and couplings. Some can vibrate enough to move them within a given area. 

Reed sensors are used to measure the magnitude and frequency of vibrations within a system, machine or equipment susceptible to frequent vibrations. 

They help ensure that vibrations do not exceed set limits. 

Sensor #3 used in a washing machine: Optical

Finally, the last type of sensor used in a washing machine is an Optical sensor.

These types of sensors detect light or a change in light levels. They can detect electromagnetic radiation from infrared to ultraviolet.

They are used in washing machines to determine the light permeability of water which can reveal things like how much dirt or detergent is present. 

Are weight sensors used in a washing machine?

You might have noticed that I haven’t included a sensor to measure the weight of the load. But, washing machines have a certain limit of weight they can handle.

So how does a washing machine know if you have exceeded the limit of weight if it does not have weight sensors?

Rather than using a sensor, the washing machine knows how much the load weighs depending on the resistance placed on the motor (how much work the motor has to do to rotate the inner tub). 

The lighter the load, the less resistance placed on the motor, and vice versa. 

If the weight exceeds the limit, the motor will not have sufficient power to rotate the inner tub. 

Would a washing machine function without sensors?

Sensors play an important role in many embedded systems, and the washing machine is no different. 

While there might be some aspects where a washing machine might function without a sensor (as we just saw with the weight of clothes), other instances, sensors are crucial and needed.

We saw the different parts of the washing machine where sensors were used earlier. Removing just one of them would cause issues. 

For example, if we removed the reed sensor which detects the water level, the drain pump would not know when to stop pumping water in, which could lead to overflows. 

So, a washing machine would not function properly without the help of sensors.

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