The Old Faithful Of Tank Level Measurement

LPD Current Loop Display


bottom tank valve perfect for installing a pressure transducerWith so many impressive technologies available to use for liquid level tank measurement, it's easy to forget about the old hand, tried and true solutions.

For example, when we get calls from our customers asking for details on measuring the level in a tank, we are often asked about technologies such as ultrasonic and pulse radar. These types are often sought after since they are non-contact, and by comparison to the other technologies, they are among the most recently developed.

We understand the buzz that surrounds them.

While these technologies definitely have their place in the market, they are not always the best choice. In many cases, it's the old reliable method that still does the job best.

This is particularly true when we learn that valves and other tank fixtures are attached to the side of the tank at the bottom. Depending on the characteristics of the liquid, this likely means that a very simple and effective method is perfectly suited for the job: pressure transducers.

There are many benefits to using a pressure transducer for level measurement when it's a feasible option. This includes low cost, ease of transportation and installation, as well as low power consumption.

Typically, once customers understand, they are typically excited that such a low cost sensor can provide such high accuracy and reliability.

How it Works

Pressure transducers are used extensively for liquid level measurement. A common type in industries we deal with is the submersible pressure transducer. Like the name suggests, they are completely submerged in the fluid and rest at the bottom of the tank. They measure the amount of pressure being exerted on it by the weight of the liquid column above it. The taller the liquid column, the more pressure is being exerted.

The math is pretty straightforward. For every psi of pressure, you get a 2.31 ft. of water. If your liquid has a different density than water, you add in a multiplier to make up the difference.

Externally mounted pressure transducers work the same way. But instead of being submerged and resting at the bottom of the tank, they are mounted from the outside. So, if the valve/pipe fixture on the side of the tank is located at the very bottom, the externally mounted transducer will measure the very same value as the submersible pressure transducer inside of the tank.

Keep in mind, though, that if you add more pipe fixtures such as elbows or couplers, this will have an effect on the pressure and will not be exactly representative of the level in the tank. However, this effect is minimal, so it's typically not a concern.

The Advantages

Using an externally mounted pressure transducer for tank liquid level measurement is one of the least expensive methods; even less than the submersible pressure transducer. This is because it's less expensive to build and the cable run is often much shorter, resulting in a less expensive unit. Of course, you’ll also get a decrease in transportation and installation costs.

Furthermore, pressure transducers don’t require a lot of energy to function, unlike radar or ultrasonic sensors. This gives pressure transducers a clear advantage in applications where power consumption is a major concern. Examples include battery-powered installations throughout a plant, or in remote monitoring of dispersed tanks.

Not a Universal Solution

Just like anything else, this method does not cover any and all applications. For example, you wouldn’t want to spend resources adding a valve/fitting to the tank to make an external transducer work if a submersible transducer was already suited for the job. If possible, it's best to find a sensor that will work with your existing infrastructure rather than adapt everything to fit with one sensor.

If you have questions about using pressure sensors for level measurement, please give us a call and we will look forward to discussing it with you further.

Explore Pressure Transducers

top photo credit: SuSanA Secretariat via flickr cc

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