CUSTOM TANK LEVEL ALARMS

We make custom tank level alarms of all types. If its liquid, we can sense it and produce an alarm if it gets high or low, or both. Viscous liquid, coating liquids, extremely corrosive, we have seen it before. 

Float switches handle 99% of all level sensing applications. They are extremely reliable, chemically resistant, low cost, versatile, relatively small size, and consume no power. Float switches should always be considered first for a level sensing project.  But what if the liquid coats the float switch and stem, then what? 

CAPACITIVE SENSORS FOR LIQUIDS THAT COAT

The next option to look at is a capacitive sensor. It tolerates a very thick coating of buildup on its surface and still functions the same as if there were no coating. Typical coating thickness tolerated is up to 15 mm.  In fact these are often mounted on the outside of plastic tanks and sense the liquid through the tank wall. However, if mounted this way, the calibration can get tricky because the tank wall thickness approaches the limit of the sensor’s range. 

Something to consider is that repeated immersions in the parent liquid tend to redissolve some of the the coating. This means that for many liquids, the coating only reaches a finite thickness. As long as the coating is less than the tolerance of the capacitive level sensor, then this is a good way to go.  Capacitive sensors have their disadvantages too, such as the fact that the capacitive sensor needs to generate a capacitive field at all times which takes power.  So operating from battery power is out of the question. The way Gizmo uses capacitive sensors is to mount them in the bottom of a plastic pipe. They are sealed from the process liquid with a thin coating of chemically inert epoxy resin.

VISCOUS LIQUIDS

Capacitive sensors are a great choice for viscous liquids. They can be calibrated so the alarm will respond when the bulk of a liquid runs off of the level probe.(but not all of it) This way the response time can be greatly reduced when compared with a float switch for example. You can see this in action in a video of our viscous liquid alarm.

Finally, capacitive sensors as small as 12mm diameter are available which is great for tight spaces.

CONDUCTIVITY SENSORS

Conductivity sensors have their place too, and this technology was the best solution for our automatic tank filling device, the Hoze Filla™ product because the device is designed to be carried around by an operator. We didn’t want the operator to have to think about keeping it vertically oriented in order to avoid an alarm while carrying it. So we use gold-plated conductivity pins which are chemically inert in most liquids. It consumes only 20 micro-amps in idle mode so the battery will last for years.

In addition, they are great at detecting very low liquid levels – mere drops of liquid. However like any sensing technology, they have their limitations too:  they are not reliable for foaming liquids as the foam can lead to false alarms. In addition, they can’t be counted on in liquids that have any kind of corrosive properties unless they are gold-plated. (Gizmo is the only company I know of that does this) And finally, they are not very adjustable: in fact some companies want you to chop the probes off with bolt cutters to shorten the depth! Interestingly, they don’t provide any instructions on how to lower the probes if you cut them too short.

THE REST

Optical sensors are great for sensing a mere trace of liquid (even better than conductivity sensors) however they must be powered with some rather pricey electronics. They are the smallest diameter level sensor available and therefore useful for interstitial spaces or wherever space is very tight. Goad company has a product using this technology called the Tankeye.

Some examples of different custom tank level controls we have created are below.ey