When it comes to measuring the level of fuels, it may feel like there are some real downers. That’s because there are a number of potential application challenges that can compromise a sensor’s accuracy. But, rest assured, there is an up side. Most fuels can be measured effectively if you choose your sensor wisely.
Here is a list of five application challenges that can de-rail your level measurement if you let them:
Vapor is a by-product of almost all fuels. It causes two problems. First, it can disrupt an ultrasonic sensor from working properly if it develops thick layers. Second, it builds pressure in tanks, which can confuse other types of sensors.
Vapor layers can become thick enough that an ultrasonic sound wave will echo off of them. This causes a false reading for the sensor. This is only a problem with thick vapor that forms into layers. Light vapor, especially if vented well, do not cause this phenomenon.
If vapor is not well vented, it can build up pressure inside of a tank or vessel. As the pressure above the liquid adds to the pressure of the liquid itself, it eliminates pressure sensors as a viable means of calculating a level. In this instance, you have to use differential pressure or a float based sensor.
If the pressure builds too much, it can overwhelm mounting threads for a sensor and push it out of its mount. While this is possible, it’s usually not a concern for fuel tanks, but the potential exists for sensors with plastic threads and housings on sealed (unvented) tanks.
To avoid an over-pressure situation, most fuel tanks are vented. But this doesn’t not end concerns over tank pressure. It really depends on the type of vent.
If the vent is open (no valve), then pressure is not a concern. However, many vents have a pressure valve in them. They release only after several psi have developed inside of the tank. This is enough to ruin the accuracy of a submersible pressure transducer, as only a few psi equal several feet of fuel.
Density, or specific gravity, determines how much volume will fill a tank. Density can vary quite a bit with temperature swings. So on a warm spring day, a half full tank will drop during the night as temperatures plummet.
The problem with variable density is not that the level changes, but that level relative to pressure changes. This is another complication for pressure sensors. Submersible pressure transducers are often our recommendation for fuel level measurement, but in this situation it’s often time to look at another option.
A small complication with fuel is that it creates a hazardous location. This is a small issue because there are plenty of hazardous approved sensors out there. However, it still complicates the application. Wiring has to be done correctly, the sensor has to have the appropriate certifications, and this effectively limits your options.
Finally, all sensors have to pass an application specific compatibility test. Fuels can be corrosive for many materials, including 316L stainless steel. For this reason, we’ve recently developed several alternatives to steel, such as a PVC submersible pressure transducer.
This is not typically a big issue, but is certainly worth a check. When a fuel is vaporous, it can even cause corrosion on non-contact sensors such as an ultrasonic.
Application success is all about putting the application first, and resisting the urge to grab your favorite level sensor and install it. We often recommend submersible pressure transducers, continuous float level transmitters, or ultrasonic sensors. It all depends on the application challenges listed above.
If you would like some help identifying your application challenges and the appropriate sensors, we’ll help you ask the right questions. Give us a call and you’ll speak with one of our friendly application engineers.
top photo credit: oregonmildep via photopin cc
