How do electronic sensors actually “sense” things


How do electronic sensors actually “sense” things

In: Technology

There’s a huge variety of sensors that can measure practically anything you can imagine. You’ll have to be more specific since they all operate on different principles.

Ultimately they’re relying on some process to change the way an electrical current flows through them, but *how* they do this is endlessly variable.

The exact mechanism depends on the sensor but they all take some physical phenomenon and turn it into an electric signal…either a controlled voltage or a controlled current. Some electronics on the back end read that voltage or current and turn it into a useful value.

Many sensors rely on changing resistance. Thermistors change resistance with temperature, strain gauges change resistance with distortion.

Themocouples change voltage with temperature.

Contact sensors (like a keyboard) can be as simple as a switch.

Hall effect sensors react to nearby magnets.

There are many (many many many) types of sensors.

It really depends on the sensor, there lot of different things to send.

Many rely on changing a property of a circuit called “resistance”, which is a measure of how the circuit *pushes back* against a flow of electricity. If I take a battery and connect both ends together with a wire electricity will flow very quickly through the wire without achieving anything, this is called a ‘short circuit’. If I place a light bulb in the wire the light bulb resists the flow of electricity and makes light & heat, and the electricity flows slower, essentially. Any element you add to a circuit that slows the flow of electricity is a “resistor” in electrical-speak.

Now let’s make a resistor that can change it’s ability to resist in response to some outside input. I can create a dial resistor that goes from low resistance on one end and up to high resistance on the other end. That’s essentially a volume knob on a TV or stereo.

Instead of a dial, let’s make a resistor that changes it’s ability in response to light, in a dark room it has low resistance and in a bright room it has high resistance. That’s called a photo-resistor and is used in things like remote controls and dimming phone screens outdoors.

I can make a resistor that changes if it gets bent or changes shape, I could use that to detect damage to bridge or building for example, or put it below a button like on an ATM or a calculator to detect button presses.

I can make a resistor that changes if it gets warm or cold and use that as a thermometer.

I can make a resistor that changes if it’s upside down or side ways and use that to sense orientation.

I make a resistor that changes to sound… to radiation… to proximity (like in a motion sensor for an alarm system) … etc etc..

There are a million sensors that work on different principles but essentially it works like this:

An analog condition (such as temperature, the closeness of a wall, the color of an object, etc.) will be measured by the sensor in one of many ways. Lets use an electric meat thermometer as an example. When two conductive metals are of different temperatures, they produce an electric current when they’re allowed to conduct heat from one to the other (this is due to some more complicated material properties outside the scope of the question). The level of current the metals produce is proportional to the temperature difference between the thing measured and the thermometer, and so the microchip in the thermometer is programmed to show a certain temperature based on the current produced by the measured substance’s heat.

This is how all electric sensors work: some mechanical force creates an electric current which the device can measure, and it displays info based on how the circuitry is programmed to read the electric current.

Most of what you’re referring to are proximity sensors. There are two kinds of *these*: inductive/ capacitive.

Inductive sense ferrous metals (magnetic because they contain iron)

Capacitive sense everything

They both have oscillating circuits that are interrupted because of an electromagnetic presence or a capacitive presense.