Welcome to this training on rotary position sensors in automotive and industrial. My name is Clancy Soehren. And today, I'm going to be discussing several different types of rotary position sensors, along with where they can be used and some of the trade-offs between them.

Getting accurate angle feedback is important for many applications. This allows the controller to know where the object that it's trying to control where it actually is. Now, any motor, for instance, an electric vehicle, the traction inverter is what actually powers the car. So if you're able to have accurate angle feedback, you'll be able to improve the efficiency and get the maximum torque when you need it.

For robotic applications, if you consider a robotic arm, the controller needs to know exactly where that arm is. Or imagine if you're in an assembly line and the robotic arm completely misses its mark. It could throw something on the floor or even hurt somebody. So getting accurate, reliable, and repeatable angle feedback is very important.

So before we actually look at the types of sensors themselves, I want to take a brief look at some of the key requirements for these sensors. First up is accuracy, precision, and resolution. These are three terms that often get confused.

Now, I've shown two targets here. One of these shows an archer who is more accurate, and the other one shows an archer who is more precise. Now, take a minute to decide which one you think is which.

Accuracy measures how close a measurement is to the true value. Precision is if you take a measurement over and over and over again how close each of those measurements is to each other. So in this example, the target on the left is more accurate. If you look at each of the points, they are closer to the center. However, the target on the right is more precise. The archer in this case shot several times almost immediately on top of each other. So that would be a precise measurement.

Resolution, on the other hand, is the smallest increment possible for a measurement. So in the example I've shown, this could be a thermometer. The one on the left could be a thermometer that reads in one degree increments. So it might read 22, 23, 24. The one in the middle might do 0.1 increments. So it might be 23.4 or 23.8. And then the one on the right is in 0.01 degree increments.

So clearly, the one farthest on the right has the highest resolution. However, this does not necessarily mean that it is more precise or more accurate. The accuracy example if the true temperature was actually, say, 24.5, then the one on the left, 24 degrees, would be the closest in accuracy.

Now imagine if you turned each of these thermometers off and then turned them on again. If it displayed a number that was close to the original number, then it would be more precise. However, if you took five measurements, and they were all wildly different, the precision would not be as high.

Another parameter to consider when you are comparing sensor solutions is the linearity of the system. Sometimes this will be expressed as INL and DNL, which is integral non-linearity and differential non-linearity. And what this means is, for instance, INL is if you examine the whole range 0 to 360 degrees, you're looking for the point where it is farthest away from where it should be. And then DNL, of course, is looking at basically the step sizes from code to code.

Another parameter to look at is the step response and latency of the system. Some sensor types will have almost an immediate response. So you wouldn't have to worry about the step response time. Other systems, you will see when you're looking at data sheets. You might see step sizes from 0 to 10 degrees or 0 to 180 degrees. And then you would see how their system responds.

In the two examples I'm showing, you'll see the line in red is an under-damped system. So it responds quickly, but there might be some ringing. And then the line in blue is almost over-damped. So it takes longer to finally settle to its value, but there's less overshoot.

And latency is the delay between when you get your angle output and when that angle actually occurred. In addition to what we've already talked about, there are few more parameters. In interface, you have to decide if you need serial, parallel, or even an encoder type output, which is very common in industrial. You'll also see that different types of sensors will have different maximum speed requirements.

And finally, the environmental conditions will be very important. So this is the temperature, if there is vibration, noise, dust, maybe magnetic interference. All of that will play into the environmental conditions, as well EMI and EMC. Of course, cost is always important. And you'll often also have to look at if the system needs any functional safety.

Now that we've looked at the requirements, let's take a look at some of the different types of sensors. So here's an overview of the different types of sensors. So on the top are the Hall effect sensors. So these will be typically lower resolution, but much lower cost.

Then we move into the middle with magneto-resistive sensors, also called AMR or GMR. And these are kind of the newer Hall sensors. And they have better accuracy. And you typically need less sensors in the system.

In the middle is our resolver sensors. These have decent resolution, but they'll also be higher cost than your Hall sensors. And then finally at the bottom are the optical encoders. These can be extremely precise, very high resolution, but they typically are more expensive.

Taking a closer look at the Hall sensors, you'll see we have a few different types. Now, on the top is the digital output type. So this would be where you have several magnets that are positioned on a rotor shaft. And you'll have several Hall sensors that are positioned around the stator. And these sensors will be able to detect when the magnet passes by. So the output will either be on or off.

In these types of systems, you have to either add more magnets, more sensors to get greater resolution. For the analog output type, instead of just doing it on or off, you're able to see the values in between. So this means you might be able to use fewer sensors. This also could be used for linear type applications where you want to see how far away something is.

The magneto-resistive sensors are even higher resolution than the other types of Hall sensors. As I mentioned, you'll typically need multiple Hall sensors and magnets to get better accuracy. However, for the AMR type sensor, you'll often only need one sensor and maybe one magnet. And it's able to detect the position of the magnetic field to determine the angle.

A resolver sensor is basically a rotating transformer. So the only things in the actual sensor itself are inductive coils. This makes it very well-suited for harsh environments. So this would be places with high temperature, dirt, noise, dust, vibration. All these cases, resolver sensors are a great choice.

Now, because it is inductive coils, the size of the actual sensor will be bigger than a Hall effect sensor. So the cost will be a little bit higher.

For resolution, you will see from 10 to 16 bits of resolution for resolver sensors. Another thing to note is that the resolver sensor is an absolute position sensor. So even when you start the device, when you turn on your circuit board, you'll be able to fairly quickly see what angle you're out without actually turning the motor. This is not always true for Hall effect sensors.

Finally, we have optical encoders. So these shine a light through a screen that has notches in it. And the light detector on the other side is able to detect the pattern of the light to determine the angle. So these can be, as I mentioned earlier, much higher resolution than even resolver sensors, but the cost also goes up.

These come in two different types-- incremental optical encoders and absolute. Incremental means that the sensor can determine how far it was rotated from its starting position, but it will need to go through a full revolution to go to there's usually a zero crossing mark that it can detect. So you have to go through the entire 0 to 360 degrees potentially to find the zero point. Versus an absolute an optical encoder which will be even slightly higher cost. And at any given point you can know exactly which angle you are at based on the pattern of the light.

Now, optical encoders, as I mentioned, they have great resolution. However, they are not going to be as well-suited for harsh environments with moisture or lots of noise or even dirt or dust that could interfere with the sensor.

The final type of sensor that I'm discussing today are inductive sensors. Now, these work by having a PCB coil and then a metal target. And depending on how much the metal target covers up that PCB coil will determine the inductance that can be measured in the system. So an inductance to digital converter will measure the inductance and then output the angle or position information. So this concept can be used for rotary position or even lateral movements as well.

The big advantage here is cost. This is a very inexpensive solution. And depending on your coil design and your metal target will determine the accuracy and the speed, the maximum speed that you can obtain.

This brings us to the end of this introductory training. Now you've seen an overview of some of the different types of sensors. And you should have a good idea of what to look for when you're looking at the different data sheets and system parameters when you're designing your system. Thank you very much.