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:
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?
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.
An artificial lift is a device used in the oil and gas industry when there is insufficient pressure necessary to lift fluids from a oils well to the surface in already-drilled wells or in new wells, to increase the flow rate above what would flow out naturally. You can see what an artificial lift looks like in the picture to the right.
Hydraulic cylinders are used in the valve systems of artificial lift systems to move fluids in and out of the process. An explosion-proof transducer is the perfect choice for mounting inside the cylinders for valve control, as it is a Class 1, Division 1 Certified unit that can be used in these potentially explosive environments (pictured at bottom).
The July 2011 issue of Hydraulics and Pneumatics magazine featured an interesting application story about how hydraulics systems were designed and used in the “Spiderman: Turn off the Dark” Broadway musical. The article describes some of the challenges faced by motion systems designers, and how those challenges were solved.
One particularly challenging aspect of the hydraulic motion systems was the requirement that multiple hydraulically driven platforms had to be raised and lowered simultaneously. The motion of the platforms had to be very precisely controlled, making hydraulic component selection critical.
When it comes time to choose a linear position sensor, there’s a dizzying array of options and terminology to wade through. In this series of articles, we’re going “back to basics” to try to shed some light on the sometimes confusing world of linear sensing options, technologies, and terminology.
First up, we’re going to take a look the two basic linear sensor measurement types: absolute measurement and incremental measurement.
I am experiencing the future of tradeshows; a networking & educational conference without the travel, the expense, and the suit! I can sit at my desk and make contact with future vendors and customers. The online database GlobalSpec hosts multiple times per year industry specific virtual tradeshow events. There are presentations and exhibitors. A place to sit and drink virtual coffee with your peers and of course the token giveaway raffles.
Today I am working the Balluff booth in the Sensors and Switches Virtual show. It is a collection of companies and attendees from many different industries. I really enjoy these events because we can contact quickly with potential customers and potential vendors right from the comfort of our conference room and at a much reduced cost. Here you can see our hard working staff chatting with customers.
In my last entry, I talked about using a magnetostrictive linear position sensor in a hydraulic cylinder. I received a few questions about that application, and I wanted to take this opportunity to answer one of them.
Q. Why is it necessary to use a non-ferrous spacer to attach the magnet ring to the face of the hydraulic cylinder’s piston?
Peter Nachtwey of Delta Computer Systems has written an excellent primer on electro-hydraulic motion control. In addition to many design and component selection tips, he highlights the benefits of magnetostrictive linear displacement transducers (MLDT) for position feedback to the controller. Check out the article in the July edition of Design World online, called “A Second Look at Electro-Hydraulic Motion Control Systems.”
Today, we’re going back to basics with one of the most common applications for linear position sensors: hydraulic cylinder position feedback.
Magnetostrictive linear position transducers are commonly used in conjunction with hydraulic cylinders to provide continuous, absolute position feedback. Non-contact magnetostrictive technology assures dependable, trouble-free operation. The brief video below illustrates how magnetostrictive position sensors are used with hydraulic cylinders.