New generation of high performance MEMS gyros prepare to tackle harsh environments
Earlier in the month Analog Devices, Inc (ADI) unveiled three new high-performance, low-power iMEMS gyroscopes with analog output specifically for angular rate (rotational) sensing in harsh environments.
The ADXRS642, ADXRS646, and ADXRS649 incorporate ADI’s advanced, differential quad-sensor technology, which rejects the influence of linear acceleration and vibration to enable these new MEMS gyros to offer exceptionally accurate and reliable rate sensing even where severe shock and vibration are present.
The new MEMS gyros offer linear acceleration sensitivities as low as 0.015°/s/g which compares with 0.1°/s/g which is currently offered by the leading alternative MEMS gyros.
The ADXRS64x series is claiming 10 times lower power consumption at 3.5 mA which compares with other MEMS gyros that consume as much as 60 mA. The device also benefits from much faster start- up times, as fast as 3 ms.
eeNews Europe: So what are the design engineers looking for in these high performance applications?
Meyer: The three top things that design engineers look for are:
1) Bias stability, or what some people call drift, because all gyros drift over time. The better the gyro the less the drift over time and also the more expensive the gyro.
2) The vibration and shock immunity. How resilient is the product for giving you a true reading when it is in an environment that’s not just nice and clean and stable.
3) Noise because people want a low noise floor in order for them to get an accurate reading and not be interfered with.
Those are huge and if you look at all the consumer gyros you will see that those stats are not specified and the reason they don’t talk about them is that they would look very, very poor in that aspect.
The customers that are looking for high performance are going to be looking for those numbers. If they don’t see them they will go elsewhere. When you look at these new ADI products that is what they are designed all around. Those three top criteria.
The thing that will make these products so popular is the fact that of those three things I have talked about, drift, immunity and noise, two of the three things can be compensated out. I can work on the system and I can make the drift lower if I put a lot of software in or I use multiple gyros and do law of averages I can compensate and make drift better.
I can do the same thing for noise. I can again do law of averages, use multiple products I can try to use filtering. There is a bunch techniques I can get to over exceed the specs of the device and get it lower overall but the immunity to the environment is extremely hard to supercede. It is difficult to go above that and compensate for a gyro because it is external events that you can’t take and work around very easily. You could use things like rubber mountings but there are a lot of limitations to how those work and they also interfere with the true readings of the product.
eeNews Europe: What makes the new generation of gyros more effective?
Meyer: In the case of these products we have a quad sensor and in previous generations we had one proof mass oscillating up and down.
The way gyros work is that you measure the Coriolis effect or the fight of the rotation because something oscillating in a North-South direction when you try to turn it is going to fight that turn because it tries to hold back.
What we are basically doing is measuring the fight. The harder the fight the more the rotation is. The whole conversion of the output of the sensor through the signal processing tells you what that rotational element is. The issue with one single proof mass is gyros can be tricked into thinking that even though there is linear acceleration and not rotational movement if you have linear movement in certain directions it can be tricked into thinking it is all rotation and you get a false reading.
So you can start adding in multiple proof masses in order to cancel out the false readings. This product has four proof masses all orthogonal to each other at 90 degrees. In which case they all work together and they isolate out any anomalous readings and only let through true readings and it is very effective at eliminating external environment and oscillation shock and the vibration that could be misconstrued as rotation. That is very important when you are dealing with applications that have a lot of movement. If you think of anything that is in flight or any type of stability for trucks or cars or even boats that are on the ocean and have wave motion and movement. You don’t want to have erroneous conditions telling you that you turning when you are not. You just want to know when you are truly turning and that is what this family of gyros is extremely good at doing. We have this quad sensor that is able to pick that out.
We now have four generation of gyros. We have increased their performance every time. So you not only have to have a good sensor element but you also have to be very good at the signal conditioning side of things which is basically the ability to take all that data that isolated what you want and be able to deliver it to the customer with high reliability and the specs they are looking for. That is what ADI has done for many years because we are a very high performance signal processing company.
eeNews Europe: What type of applications will these MEMS gyros support?
Meyer: This ADXRS64x family is pin and package compatible to our ADXRS62x family which had two proof masses. Now we have four so this is a drop-in performance upgrade to this popular family.
We have four derivatives with different ranges of detection 250 °/s, one 150 °/s, 300 °/s. These drop right in but give you better performance. Then there is the ability to take it even higher. We have a very good bias stability when you look at 8 °/hour that’s going into tactical grade.
If you think of what is driving something like an Apache helicopter or a Boeing 747. You are talking 1 or 2 °/hour and there is a cost for that versus at the complete other end of the spectrum a consumer gyro. A consumer gyro is very low cost and does not have the specs in the system so those gyros probably drift more than 100 °/hour. So you can see what a wide gap there is.
This ADXRS64x family goes down to 8 °/hour which is very high. Our previous generations started out in the 50 °/hour then we went to 40 °/hour range. The ADXRS62x generation is about 25 °/hour and this latest generation drops all the way down to about 8 degrees/hour. The rate noise density is very low at 0.01°/s/√Hz (0.6°/√hr) and that’s quite impressive. One of the family members does go above and beyond 20,000 °/s and all the way up to 50,000 °/s.
There are applications that need that high a rate such as industrial applications where you can do the translation to rpm by 20,000 °/s or 50,000 °/s. You can have motors and shafts and detection of devices that are turning at a certain rpm that we can now look at and there are also some medical applications for example relating to concussions. This gyro has been placed inside a helmet that is going to be used in the armed forces for detection of traumatic brain injury because when you have an explosion that is nearby a soldier’s head it makes a very quick move from a blast impact and the gyro measures that rotation and we are talking thousands of degrees/s. We can measure that rotation to determine the effect on the human body and possibly see whether the soldier has suffered any type of concussion. Right now they just don’t know and if it is not visible then the solder can go on and say they feel fine and they go back out there and they are at risk especially if they happen to run into something again.
This kind of thing is even happening in contact sports. Athletes are running the risk of permanent damage because you have run into an incident that has given you some type of concussion or brain injury and it goes undetected. Those are examples where you can use a really high rate.
We are also talking about places where gyros are needed but they have never been able to go before such as intelligent harvesting in agricultural applications.
Here GPS accuracy has to be very accurate to enable this equipment drive itself day or night without going erroneously into the field and keeping track and right on line over a mile or kilometre of a field without straying by a couple of degrees and by the time you are at the other end of the field you are a couple of metres off. All of that stuff is taken away so that you get maximum productivity.
You may also want to do surgical navigation where the measurements inside the human body need to be very precise. The there are First responder applications with emergency services such as fire fighters or ambulance crews need to know where they are going into buildings or are entering a place where there is no GPS signal and they can’t rely on the accuracy of what is coming off the satellite. In these case you have to go a true autonomous system which is GPS free and you can rely completely on
Another example would be emote guidance and factory automation applications which are all harsh environment conditions where there is a lot of movement and a lot activity going on and you want to isolate out what is anomalous.
We actually have customers in Europe under non-disclosure agreements that already have ADXRS646 and ADXRS649 samples.
Our iSensor line of IMUs makes ADI unique from our competition. There are actually quite a few IMU companies around the world that use our components to make their own IMUs and there are quite a few in Europe.
We have already engaged with some of them and they have some of the silicon because they are really look for the new drift capabilities and in this case a lot of the noise issues.
The lower the noise then the higher the performance of the IMU. So that is pretty popular. Keep in mind this same quad sensor is on automotive versions and we have a huge automotive side to our MEMS business and that is very well engaged with automotive which is of course key in Europe. There are automotive versions that have this style quad sensor on and we are heavily engaged with these in Europe.
There are also a lot of industrial applications in Europe where this is very applicable. The ADXRS62x series sells very well in Europe and this is a performance upgrade so we expect it be popular.
eeNews Europe: What do you believe are the key parameters that make a high performance gyro?
Meyer: The two key vibration immunity specs are vibration rectification and sensitivity to linear acceleration. This family of iMEMS gyros provides vibration rectification of 0.0001° /s /g2 which is three times better than Honeywell and seven times better than Silicon Sensing (according to data sheet comparisons).
It is really about the immunity, the processing and the integration. That is really our thrust. We believe we are an order of magnitude better than anyone in the competition and that is because of the quad sensor. Our power consumption is also much lower. You can see single digit current consumption (3.5 mA to 5mA) versus 45 mA and mid 50 mA in competitive products. Then there is very low noise overall on these products.
So have a good blend and a really quick start up time. Most gyros start up in 60ms, 50ms or 40ms and what we have now goes down to 3ms. They are very low power consumption devices.
The highest performance version of the ADXRS64x family has the best bias stability or drift. It has the best vibration immunity and has the best noise density of all the products currently on the market.
At ADi we offer components such as gyros, accelerometers and inertial sensors but in many cases customers like to roll their own and write their own software. On the other side ADI offers full-blown inertial measurement units, IMUs that can be put inside a sensor module that has calibration built into with a micro. They are called iSensors and they are ready to go out of the chute, calibrated 24/7 you basically just drop in and go. So all of the work is taken out of the equation and it is just a ready to do solution.
eeNews Europe: The power consumption figures look interesting. How have ADI kept them so low?
Meyer: Part of the expertise is not only the sensor itself but also the signal processing. We do a lot of low power stuff amongst our company and share best practices and that can be anywhere from our processors to our codecs and amplifiers so that really has to do with the expertise of the design engineering where they put all the signal processing side and the non-sensor element and work to make that as efficient as possible. So those numbers are not new to our gyros. If you go back to our ADXRS62x family they are also very low. They are single digit also. Those numbers have been around for a while.
eeNews Europe: How large do you estimate the market for these products is worldwide?
Meyer: These products are higher priced than accelerometers. It is not millions and zillions of units because it is not going into an iPad but the market is quite healthy. If you took out automotive sector then the market for these gyros is $100m to $200m units of opportunity out there. That doesn’t add in the iSensor modules or IMUs. From a component standpoint we are probably talking $200+ million non-automotive and when you add the whole iSensor type IMU market it probably goes well above $500+ million.
eeNews Europe: So to summarize what would you say are the major benefits are for the new gyros?
Meyer: I would say the immunity is certainly the No.1 because that quad sensor really does break things for this product. The drift is very good but I would probably say the power consumption is excellent. The start-up times are great. So No.1 is immunity. No.2 is power consumption and No.3 is a toss-up on the drift and the noise and the start-up time. I would probably go with the noise. The drift is very good but there are some that are a little better but we are already down into single digits. I just think all around it’s a very diverse and well rounded product.
eeNews Europe: So what is the next generation of gyros going to be doing? What’s the next direction?
Meyer: We will always be looking for better performance. So that can be taking things in many directions in terms of the bias stability. Our sensors become more integrated to give you more features. Our sensors do anything from combinations of adding four-, six- or nine-degrees of freedom by adding in accelerometers or magnetometers. So high integration is very big and in order to get to the point where you can get into these high performance applications because customers are constantly asking for more you can expect to see more integration, better specs for the three key parameters – immunity, drift and noise – and being able to deliver that in a very cost effective product.
eeNews Europe: In terms of the quad sensor technology is there any way you can improve on this in future products?
Meyer: Do we have to take it even further? I am not sure it makes sense to go eight sensors and do even more vibration analysis but there is a way to make them connect more in order to work better together to isolate more that is very possible. But we haven’t really looked at how to take the quad even further yet. Some people now want digital gyros. We might look at how to do that in multi-axis systems because there is a lot of that needed. So it is probably taking that same performance and putting it in different directions such as multi-axis solutions.
Low-power iMEMS gyros offer high performance benefits under harsh vibration
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