So, you find yourself in need of a sensor. It happens to the best of us. How do you decide which sensor to buy? Or even what kind of sensor you need? Before you choose a vendor, you have to know which product you want them to provide. So how do you decide?
Today, let’s ask the Application Questions. A thorough interrogation of the application will lead you to the kind of sensor that best matches your needs. As far as choosing a specific sensor and vendor goes, though, you’ll need to do your own homework for that.
Every measurement is a quantification of something: “How much of this stuff do I have?” It’s an important question, or you wouldn’t be asking it, but in that form it’s not a precise question. Do you need to know weight or mass? Volume or pressure? Flow rate? Temperature? Air-speed velocity of an unladen swallow? Determining what you need to know—rather than what you want to measure—is the first step to determining what kind of sensor you need.
“Ok, but if I need to know level, I should just get a level sensor to measure level, right?”
Nope. You can get level from a pressure measurement, a distance measurement, an open-close switch, or even a series of open close switches. That’s why it’s so important to answer all the questions before jumping to “I want a level sensor.”
The next step is to identify what kind of substance you need to measure. Is it a liquid, solid, or gas? Is it in motion, or usually still? If it is a solid, does it have a fine granularity (like sand or salt), or coarse granularity (like mixed gravel)? Is it susceptible to dust, mist, foam, or vapors? Is your substance corrosive to metals or plastics? Each of these properties will highlight or eliminate a sensor type.
So you’ve determined what you need to know, and what you need to know it about, but where do you need to get that information from? Does your measurement need to take place in a classified Hazardous Location? Will your sensor need to intrinsically safe? Explosion proof? Impenetrable by vapors, dust, or liquid? While these questions seem more pertinent to selecting a specific sensor as opposed to a type of sensor, some sensors types and technologies lend themselves to Hazardous Location certification more readily than others.
The last question we’ll look at is the question of output: What kind of output do you need? Do you need continuous monitoring with an interface to an existing control system, preferably running standard with a proven standard like Modbus or Hart? Or maybe an occasional measurement with a local audio/visual alarm? What about remote control, say via internet? Perhaps you’re just looking for a simple, proportional analog output, say 4-20 mA, 1-5 VDC, or even mV/V. No matter the output or communication specification you need to meet, there will be a sensor that can accommodate you. But you have to know what you need before you can choose.
In the end, the sensor you choose as your answer will only be as good as the questions you asked. If you take the time to interrogate the application, rather than rushing to “I just need this kind of sensor,” you give yourself a much better chance at success. With so many sensor technologies available, each of the questions above will help you find the best sensor type for your application. But you have to ask the questions.
And speaking of questions, if you’ve got ‘em, we’d love to help you find answers. Since we manufacture several types of sensors in-house, we’re intimately familiar with all the application questions, and can help you find the perfect sensor type for your situation, even if it isn’t one of ours.
top image credit: Brian Boucheron via flickr cc
