In this video, we're going to introduce you to a device called a Limit Switch.
There’s probably not a day that goes by
where you don’t use or encounter a limit switch at home,
or at your workplace.
There are 4 general types of limit switches:
whisker, roller, lever, and plunger.
Depending on the application,
a limit switch may be a combination of 2 of the general types
such as roller-lever.
OK….let’s get started.
A limit switch is an electromechanical device
operated by a physical force applied to it by an object.
The limit switch is used to detect the presence or absence of an object.
These switches originally used to define the limit of travel of an object,
and as a result, they were named "Limit Switch".
When you open the fridge door, a light comes on inside?
How does that happen?
Yes….you guessed it!
A limit switch is used to detect if the fridge door is open or closed.
Let’s look at another application of a limit switch that you may encounter at home.
On many overhead garage doors,
there is a limit switch that stops the movement of the door
when it reaches its fully opened position.
Alright….now that we’ve looked at a couple of limit switch applications
where you might see them in action at home,
let’s have a closer look at the device itself.
A limit switch is an electromechanical device consisting of an actuator
mechanically linked to an electrical switch.
When an object contacts the actuator,
the switch will operate causing an electrical connection to make or break.
Limit switches are available in several switch configurations:
Normally Open, Normally Closed, or one of each.
Depending on the origin of the electrical schematic,
you may see limit switches drawn in different ways.
The International Electrotechnical Commission or IEC
and the National Electrical Manufacturers Association or NEMA
have slightly different symbols.
Let's have a look inside a microswitch that is a type of limit switch.
A microswitch has 2 limit switches operating together
and sharing a common terminal.
One limit switch is normally open and the other is normally closed.
To be technically correct, the switch configuration
is Single Pole Double Throw,
or commonly referred to as SPDT.
The dashed line indicates that both switches are mechanically connected
and will operate at the same time.
Alright, let's connect the microswitch to a lamp circuit.
In the inactive state, the Red lamp is on
as the device is not being operated by an object pushing on the trigger.
When the Trigger is pushed the device will activate,
and the Green lamp will come on.
Now that you've seen the limit switch in action
you are probably thinking about some of the applications
where you have seen them in action.
For example, you might see a limit switch operated by a container on an assembly line,
or operated by a rotating machine part
or by any number of other moving mechanical objects.
A limit switch could be used to count passing objects,
or determining the position of a hydraulic cylinder.
Limit switches are slowly starting to disappear from many industrial applications.
They are being replaced by proximity sensors.
Unlike a limit switch, a proximity sensor has no mechanical moving parts.
A proximity sensor performs the switching action with "electronic" switches.
Limit switches will not completely disappear any time soon
as they outshine their proximity switch counterpart in their ruggedness
and reliable operation in difficult environments.
Generally speaking, limit switches are capable of handling much higher current values
than proximity sensors.
If you want to learn more about proximity sensors and other types of sensors
check out our other video called
“What is a Sensor? Different Types of Sensors, Applications”.
You can find the link to this video in the description.
OK… let’s review what we’ve covered in this video…
There are 4 general types of limit switches:
whisker, roller, lever, and plunger.
A limit switch is an electromechanical device
operated by a physical force applied to it by an object.
A limit switch is an electromechanical device consisting of an actuator
mechanically linked to an electrical switch.
Limit switches are available in several switch configurations:
Normally Open, Normally Closed, or one of each.
Depending on the origin of the electrical schematic,
you may see limit switches drawn in different ways.
Limit switches are being replaced by proximity sensors in many applications.
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