Tag Archive: Ultrasonic


Sensing temperature

Like I said already a few times is that we use ultrasound for our thesis, I also mentioned that the speed of sound is reliable of temperature and humidity.

So let’s have a closer look at how we measure temperature with sensors, I found this interesting comparison between temperature sensors so I’ll summarize it for you guys.

There are two types of sensors to measure temperature, the contact and the noncontact ones.

 

 

Here are the most common contact temperature sensor types:

A thermocouple uses two metals to create a voltage that is dependent of the temperature difference between the ambient and junction temperature. This is already a big advantage because it doesn’t need extra power and it’s also very cheap. They are robust but decay over time and can measure a big range going up to 3,000°C and as low as –250°C. Thermocouples are often used in ground vibration tests.

Thermistors (NTC and PTC) work somewhat like an LDR (light dependent resistor), so it’s a resistor which his resistance value is dependent of its temperature. These are often used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements. So like you see they are mostly used for simple temperature measurements.

Resistance temperature detectors (RTD) are also resistors (thin-film or wire-wound) with a resistance value which is dependent of its temperature. They are very accurate, robust and stable because it’s made of platinum, which is not affected by corrosion or oxidation. Thin-film RTD elements have a thin layer of platinum for its resistor and are used for Health & Usage Monitoring Systems.

 

 

The noncontact types are represented by the infrared temperature probes.

So every object that has a temperature above absolute zero emits Infrared radiation which is linked to its surface temperature. So by using an infrared sensor you can measure it, but you still need some electronics afterwards to process the data into something which is readable for the user.ScreenHunter_4

A problem with the use of infrared probes is that the object you want to measure needs to be bigger than the measurement spot like you see here:

measurement spot

One of the big advantages is that they can be used from a big distance and they can measure high temperatures because they don’t contact. Also measuring moving objects is an option.

 

 

 

So hope you now know a bit how they measure temperature in the world of electronics. What would you use to measure the temperature at home?

Measuring a distance

So in our master thesis, we need to measure a distance between two nodes with ultrasonic waves. So I was wondering, what ways can you measure distance.

 

Should I use a measure tape, an Ultrasonic Distance Meter or a Laser Distance Meter?

 

What is the problem with a measurement tape, it is not very accurate and it doesn’t ease the work of the user. Why do we still use it then, first of all it’s very cheap and easy to handle and use. It has also a lot of shortcomings, like how to measure something when object are in the way. Also it is difficult to measure long distances when you’re by yourself.

File:Tape measure colored.jpeg

So how can we overcome these limitations, let us use a more “intelligent” measuring system. These digital measurement tools use electronics to ease the work of the user, like knowing how to use Pythagoras.

A Laser as well as a Ultrasonic Distance Meter, sends out a burst and waits for the signal to reflect back from the object and then measure the time it took. The only difference is what kind of burst it is, a laser uses a burst of light. Logically an Ultrasonic meter uses an ultrasonic sound burst to measure distance. There are some differences between light and sound, light is more directive and travels in a straight line, at a velocity of 299 792 458 m / s which is dependent of the used wavelength and  medium. While sound travels with a speed of 340.29 m / s and is dependent of humidity, pressure and temperature because it needs a medium to travel through. It propagates less directive, it sends out a cone (like you see on the picture underneath).

beam width

In general are laser distance meters more accurate, this because they use more focused bundles so they have a bigger range and light is less dependent of external factors. But the components to measure this are more expensive because they need to work at higher clock frequency. We use Ultrasound in our thesis, because we only need a range of about 10 meters, which is viable for Ultrasound and find it beneficial that that a transmitter sends out a cone of ultrasound, because then multiple receivers can receive the transmitted burst. It is also less sensitive to the time errors because sound propagates at lower speed, so the time error of the electric signal that needs propagates trough the cable is more negligible.

 

What would you choose to measure distance, the Laser or Ultra Sound? You can read this small paper, because it is a good comparison and my post is also based on it.

Nature inspired ultrasonic distance measurement

An animal that uses ultrasound is the bat, they use it to hunt at night. A lot of animals hunt in the dark, like cats and have special eyes to see in the dark. But because insects are too small to hunt even with that kind of eyes, the bat uses Ultrasound to locate insects to hunt on.

animal ecolocation
So he uses his ears to see (= echolocation). Not only bats use this method, also dolphins and whales. It’s even possible to do it as a human, Daniel Kish is blind from the age of 13 and has adapted to this, by learning himself echolocation.

human-echolocation-in-action

Not only nature uses echolocation, also submarines and cars use it, like you see on the first picture. Submarines can use sonar to check the depth of the sea or to see other objects in the neighborhood. Because we use ultrasound in our thesis I find it more appropriate to talk about the echolocation in cars.

example of park assist

Now a days every car has park assistance on it,  like you see on this picture there is already a lot of evolution in this sector.

evolution in ultrasound sensors

For the ones that don’t know how it works, the sensor transmits a burst and then he times how long it takes to receive the echo/reflection of the burst. Then he uses this time difference in combination with the velocity of sound to calculate the distance.

Because the sensors are used outdoor, they need to be waterproof. For this reason they opt for enclosed sensors, that can both transmit and receive. These types are normally less sensitive, but more robust.

An important factor, they need to choose in the application is at what frequency to transmit. Transmitting at a high frequency, makes your signal more directive, what is better to prevent interaction with the ground. For the same reason asymmetric types are used, sensors that have a bigger horizontal range than they have vertical.

directivity of higher frequencies

 

 

 

I hope you see that nature inspired this invention, you could see it as an example of biomimicry.

See you next time.

Detecting raindrops

I was driving in my car and it started to rain. My windscreen wipers automatically started to work and I was wondering how it works. So after searching I found a good blog post that explains how it works. Here you see a schematic representation of its internals:

01-rain-sensor-working-principle-reflection-of-infrared-light-electro-luminescent-diodeSo, on the left you have a LED that sends out a beam of light and depending on the amount of light that is received on the right side, the output gives a certain value. When a raindrop lies on top of the windscreen above the sensor, a portion of the LED light beam is deflected to the outside and therefore the receiver receives less light and this difference is visible at the output. This is then used to adjust the speed of the windscreen wipers.

So this can make the live of a driver easier. There can be a lot of possibilities to use this sensor for, like closing the roof of a convertible or turning on the lights during heavy rainfall.

Are there other possibilities to use the sensor for, that you can think of, which can ease the job a driver?

 

 

 

 

Extra! Extra! Read all about it!:
A new innovation in the automotive industry was recently announced, McLaren are going to use Ultrasonic waves to clear the windscreens of their super- and hypercars.

mclaren-ultrasonic-wipers

These Ultrasonic Waves have multiple advantages like, they don’t distract the driver and it is more aerodynamic than the standard windscreen wipers. The Sunday Times was the first to publish article about this topic so if you have an account I would certainly recommend you all to read it.

This new development shows another application of Ultrasonic waves than the distance measurement we do in our Thesis.