by Michael Shade, IQS Editor
It may not occur to many people that somewhere, right at this moment, a level switch in a little metal tube is measuring the conductivity of an alternating current through sludge in order to determine its level. This doesn’t occur to many people for a few reasons. First, all of the weird processes and machines on which we all rely, but of which most of us are ignorant, are always buzzing and humming away, measuring frequencies, determining conductivity and so on. We’ve become accustomed to things just working. Second, if the average person accidentally came into contact with one of these machines or processes, that person probably wouldn’t know what he or she was looking at.
Flashlight? Space hammer? Parascope? The unrecognizable gizmo is an explosion-proof ultrasonic level sensor, a device used to measure the level of a liquid without coming into physical contact with it. In what context would such an elaborate piece of equipment be necessary? You would only ask this question if you’d never stuck your head into a storage tank full of toxic chemicals. Somehow, the professionals who manage the useful but often hazardous materials that make industry work need to be able to tell how much hazardous material they have left (without sticking their heads into their storage tanks). There are a lot of words for switches like the one pictured: level indicator, level sensor, tank level indicator. The list goes on because an entire manufacturing sector is dedicated to improving the way professionals measure the levels of things; the diversity of contexts in which different stuff needs to be measured calls for a diversity of stuff-measuring equipment.
Image courtesy of SOR, Inc.
Some level switches, like the float level switch pictured above, are simpler than others. Such a level switch would be placed horizontally in a tank. When the level of the liquid stored in the tank comes into contact with the float, it triggers the sensor. One or two things could happen next. The sensor could simply indicate that the liquid has reached a certain level, or the sensor could be connected to a control mechanism and prevent more liquid from entering the storage tank. Such sensors come in handy as emergency overrides to prevent damage to storage systems, and all other varieties of level switches allow for level indication, level control or both. But level switch designs range from simple to completely baffling. For example, the capacitance level sensor that I mentioned in the first paragraph can use a low-frequency radio wave to measure the conductivity of a circuit within a rising or ebbing flow of sludge. It would never, ever have occurred to me that such a device would be necessary or even possible. But here we all are, measuring our toxic sludge without having to use a space suit and a yardstick. Wastewater treatment plants are much safer and more pleasant places to work since the creation of this technology.
But not all level switches measure the levels of hazardous materials. They’re also useful in water tanks, grain silos, road salt storage spaces and a huge number of other places. A rotary level switch, which is a kind of mechanical level switch, is a little spinning windmill that is used to measure the level of granular solids in places like grain silos. Between three and six of them can be placed in a given silo from bottom to top. As grain enters the silo, it causes the windmills to stop spinning, one by one. When they all stop spinning, the silo is full. Simple optical level switches might even have a presence in your home. Have you ever tried to close your garage door when your car was parked right under it? While this question may bring traumatic memories and expensive repair bills to mind for some of us, others will think of the little infrared sensor that, when its beam is interrupted by something (like a car), keeps the garage door from closing. That same technology is used to prevent tank overflows and serves other level detection functions. Have I lost you? Well, you are now free to resume ignoring the level switches around you. But know this: if it weren’t for level switches, you may have found yourself sticking your head in a tank for a living.