What Is A Tank Strapping Chart?


tank level measurementWhen volume is a concern, your tank might just come with a strapping chart. But what exactly is a tank strapping chart? A tank strapping chart tells you the volume of liquid that is in your tank at a specific level. For example, when your tank has a level reading of 5 inches, you may have 5 gallons of liquid, and at 8.5 inches, you may have 10 gallons. A tank strapping chart helps you easily and quickly convert these levels of measurement into volumes. This is especially useful for non-linear tanks.

You might also hear a tank strapping chart being called a tank calibration chart, strapping table or other names. No matter what it is called, a tank strapping chart is an invaluable tool for ensuring your level measurements are accurate.

Tank Strapping Charts For Non-Linear Tanks

Non-linear tanks need strapping tables to identify volumes at given levels because they cannot be calculated with simple equations. These tanks are calibrated by the manufacturer or a professional service to ensure an accurate volume can be calculated at important level intervals.

Common Strapping Chart Features

6.97 177 1 159 42
9.96 253 2 318 84
12.56 319 3 477 126
15.08 383 4 636 168
17.64 448 5 795 210

The essential information in a strapping chart is primarily a height, or level, measurement paired with a volume. The level measurement can be converted to gallons, barrels, liters, or some other unit of volume. The purpose of a tank strapping chart is to convert a linear level measurement to a volume, which is often a more useful measurement.

Strapping tank charts are not standardized and will need to be made to the specifications of the tank. For example, 5 ft of liquid in a small process tank is very different than 5 ft of liquid in a large terminal tank. If the manufacturer of your tank does not provide strapping chart calculations, you can always find professional service that will create a strapping chart for you. If you use level sensors, they might have the ability to put your strapping chart directly into the sensor also.

The resolution of the increments can vary. Some measure every inch; others may use feet. Volume is often the primary increment; an oil tank might only show a measurement for every barrel (42 US gallons).

A combination of units of measurement is common. For example, you’ll often see levels measured in both inches and millimeters, and volume in gallons and liters. So how do you use a tank strapping chart?

How To Use A Tank Strapping Chart?

This may seem obvious, but you use a tank strapping chart by comparing level measurements to convert to a volume. However, with modern day level sensors, either the sensor or the control system does this for you – unless the tank isn’t linear.

Level Sensors

Not all tanks are linear. In fact, many tanks are irregular and they will not produce an accurate volume, even with a level measurement sensor. This means you will still need a tank strapping table. But, several APG level sensors allow you to put the strapping chart directly into the sensor via Modbus programming software. These include the MPX magnetostrictive level transmitter and the MNU and MNU IS ultrasonic level sensors. Using these sensors, you will assign a volume to a series of given level measurements. The sensors will then use those known points to linearize the tank and give a continuous volume measurement.

It’s usually a good idea to use a tank calibration chart on occasion to check the accuracy of your sensor. This will help you make necessary adjustments, or even find a new sensor if needed.

Why Is It Called A "Tank Strapping Chart?"

The term “tank strapping chart,” comes from calibrating a tank by measuring it with a steel tape, or strap. Modern-day tank calibration instruments include high tech tools such as laser levels and ultrasonic thickness gauges, but the practice has humble beginnings.

So tank strapping is tank calibration, and the strapping chart is the output.

Other Terms For Tank Strapping Chart

There are several other terms used that mean the same thing. These include:

  • Strapping Table
  • Calibration Table
  • Tank Chart
  • Tank Calibration Chart
  • Tank Gauge Chart
  • Gauge Table
  • Dip Charts

You get the idea. These names all refer to a table, or chart, for converting a linear level into a volume. The common term may change a bit based on industry and location. However, the most common term as far as we can tell is tank strapping chart.

So, that is what a tank strapping chart is and how to use one. If you have non-linear tanks, a level sensor that has a tank strapping chart directly in the sensor is an easy and convenient way to measure the volume of your tanks. If you aren’t sure which sensor is right for you, our experts will help you determine the best devices for your particular application. If you have any questions about how to use your level sensor and strapping chart together for a better level measurement, contact us today - we're happy to help!

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top image credit: U.S. Department of Agriculture via flickr cc

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