In my previous posts (Ultrasonic Sensors with Analog Output, Error-proofing in Window Mode, and The Other Retro-Reflective Sensors) we covered the Ultrasonic sensor modes and how they benefit in many different types of applications. It is also important to understand the reflection properties of various materials and how they interface with the sensor selected. For example some Photoelectric sensors will have a very difficult time detecting clear materials such as glass or clear films as they will simply detect directly through the clear material detecting what is on the other side giving a false positive target reading. As we know, this is not an issue with an Ultrasonic sensor as they detect targets via a sound wave so clear objects do not affect the sensors function. When looking at sensor technologies it is import to understand the material target before selecting the correct sensor for the applied application such as an Inductive sensor would be selected if we are looking at a ferrous (metal) target at short range. Below are some examples of good and poor reflective materials when Ultrasonic sensors are used.
Good Reflective Materials
- Hard Rubber
- Hard Foam
Challenging Relective Materials
- Cotton Wool
- Soft Carpet
- Soap Foams
- Powders With Air
- Soft Foam
- Soft Rubber
So as you can see materials that are hard or solid have good reflective properties whereas soft materials will absorb the sound wave provided from the sensor making it much more challenging to detect our target. For more information on Ultrasonic sensors click here.
Many times in an application we need more than a simple discrete on/off output. For a more accurate detection mode we can utilize analog outputs to monitor position, height, fill-levels and part presence typically found in object detection assemblies. When utilizing Ultrasonic sensors with an analog output we can simply measure the distance value that is proportional to the distance of our target within the operating range of the sensor. Typically 0…10V or 4…20mA outputs are available with the option of rising or falling characteristics. Rising and falling is a way to invert the view of the output, so 0…10V would simply be inverted to 10…0V or 4…20mA would be 20…4mA.
Ultrasonic sensor offerings are a great alternative as they can deal with difficult targets that are typically a challenge for other sensor technologies. They also offer very good resolution with the options of long and short range detection. Below is an example of a 4…20mA linear output. As you can see the closer our target gets to the sensor face it indicates an output closer to 4mA and the further away from the sensor it will provide and output closer to 20mA. For more information on Ultrasonic sensors, click here.
A question came in recently concerning the maximum recommended cable length for analog sensors. Even as digital interfaces gain popularity, sensors with analog interfaces (0-10V, 4-20 mA, etc.) still represent the overwhelming majority of continuous position sensors used in industrial applications.
The question about maximum cable length for analog sensors comes up pretty frequently. Generally speaking, the issue is that electrical conductors, even good ones, have some resistance to the flow of current (signals). If the resistance of the conductor (the cable) gets high enough, the sensor’s signal can be degraded to the point where accuracy suffers, or even to the point where it becomes unusable. Unfortunately, there is no hard and fast answer to the question. Variables such as wire gauge, whether or not the cable is shielded, where and how the cable is routed, what other types of devices are nearby, and other factors come into play, and need to be considered. A discussion about all of these variables could fill a book, but we can make some general recommendations:
Continue reading “Cable Length for Analog Sensors”
I recently had a conversation with a customer that resulted in one of those forehead-slapping “duh” moments for me, and I thought it might be worth passing along. Here’s the story:
The customer had an application that required an analog linear feedback sensor that provided an output of 1 volt to 5 volts over the linear stroke range. Now, a 1-5V output is not very common, and the particular sensor he was interested in was only available with either a 0-10V or a 4-20 mA output. What to do? Perhaps the answer should have been obvious to me, but it was the customer who provided the solution this time: “couldn’t I use a 4-20 mA output and 250 ohm resistor to get my 1-5V output?” Why, yes….yes you could (smack…..duh!). And I know it will work, because we have the law on our side. Ohm’s Law, that is: E = IR, or voltage equals current x resistance.
Let’s check it:
4 (mA) x 250 (ohms) = 1 (volt)
20 (mA) x 250 (ohms) = 5 (volts)
So there you have it. Take a very common 4-20 mA output and drop it across a 250 ohm resistor and, lo and behold, you have your less common 1-5V signal. And, if you do this conversion right at the input to the controller, you get the added benefit of increased noise immunity of the 4-20 mA signal.
And, yes, I’m sure I knew of this little trick at one time. Maybe the part of my brain where this information was stored got overwritten by the names of the contestants on The Amazing Race or by the rollout plans for my million dollar consumer product idea: Dehydrated Water (just add water). But let’s keep that just between us, ok?
To learn more about analog feedback sensors visit www.balluff.us
Everyone likes things on demand right? Movies, TV shows, chocolate, you name it. My good friend, John Harmon, has prepared a YouTube video so that you have at your fingertips an on-demand presentation on Distributed Modular I/O. It is a great overview of the available functionality of Distributed Modular I/O and what kinds of control products that are available utilizing this technology. I realize the video is seven and a half minutes, which is pretty long for a web video, but I think he does an excellent job of keeping your attention and demonstrating the value of this technology. Grab a soda and your favorite chocolate bar, put your phone on silent, and hit play on this excellent presentation.
Continue reading “Distributed Modular I/O Demo on Demand!”
I recently had the opportunity to attend Hannover Fair in Germany and was blown away by the experience… buildings upon buildings of automation companies doing amazing things and helping us build our products faster, smarter and cheaper. One shining topic for me at the fair was the continued growth of new products being developed with IO-Link communications in them.
All in all, the growth of IO-Link products is being driven by the need of customers to know more about their facility, their process and their production. IO-Link devices are intelligent and utilize a master device to communicate their specific information over an industrial network back to the controller. To learn more about IO-Link, read my previous entry, 5 Things You Need to Know about IO-Link.
Continue reading “Intelligent Interfaces and IO-Link Innovation”
In typical sensors all you get is ON or OFF… we just hope and assume that the prox is working, until something doesn’t work properly. The part is seated but the sensor doesn’t fire or the operator can’t get their machine to cycle. This can sometimes be tricky to troubleshoot and usually causes unplanned interruptions in production while the maintenance teams attempt to replace the sensor. On some recent customer visits on the east coast, I have had a number of interesting conversations about the customer’s need to collect more information from their sensors; specifically questions like:
- How do I know the sensor is working?
- How do I predict sensor failure?
- How do I know something has changed in the sensor application?
- How do I get my sensor to provide adaptive feedback?
- How do I plan preventative maintenance?
- How can I increase the overall equipment throughput?
- How can I increase my process reliability?
Continue reading “3 Production Problems Solved by Intelligent Sensors”
There are many terms used for I/O technology in industrial automation: Remote I/O, Distributed I/O, Modular I/O, Expandable I/O, Block I/O, Conventional I/O and the list can go on. What do they all mean? Can they be used interchangeably? What is the difference?
Lets be honest… this is a muddled topic and many people use different things interchangeably. I’ve done a bit of research and reading of automation magazines, forums and websites and have tried to piece it together.
Continue reading “Industrial Network Basics: Simplifying I/O Terminology”
In many cases, the mechanical components of an older machine can basically operate forever. Critical surfaces can be remachined, and bearings and gears can be replaced again and again to restore lost accuracy and repeatability.
But what about the control system? Sometimes older machines are retrofitted with a new controller to enhance its productivity and extend its useful life. Such refits should not stop with the controller alone. Many of the greatest improvements in machine performance can be obtained by upgrading the entire sensor package as well. Sensors are at the heart of today’s automation systems. They provide the critical information and feedback about what the system is doing, and the status and condition of products being handled and produced.
Continue reading “Upgrade Sensors…Upgrade Automation Performance”
There are three general classes of position sensors that – taken together – form a position sensing hierarchy. This hierarchy applies to any underlying sensing technology, for example inductive, capacitive, ultrasonic, or photoelectric. Going from the most basic to the most advanced sensor operation, the hierarchy includes:
Continue reading “The 3-Tiered Position Sensing Hierarchy”