How to Calibrate a Positive Displacement Flow Meter

Positive Displacement Flowmeter | Flowmetrics

A flow meter is a device designed to measure the rate of flow of a fluid through a space within a larger system. In fact, the use of flow meters is incredibly common amongst businesses and other organizations including:

However, a flow meter must be calibrated properly to ensure the readings are accurate. Often, this requires referencing specific calculations and measurement standards that are set by the industry, in which the company is doing business. Regular calibration ensures that each meter is providing reliable outputs. Typically, calibrating involves making a series of small adjustments based on comparing the readings of the flow meter being calibrated and the flowrate measured by a meter that is known to be accurate.

To support proper calibration of a positive displacement flow meter, it is best to follow a series of best practices associated with performing the actions needed.

Understand that All Flow Meters Require Regular Calibration

It is important to first understand that all flow meters require calibration on a regular schedule, as well as when outputs seem inaccurate. Even the most well-made and sophisticated flow meters degrade over time, resulting in lower accuracy.

For example, corrosion or debris buildup can dramatically impact outputs, and a positive displacement flow meter can be subject to either depending on the fluid being measured and the surrounding operating conditions. With that in mind, the only way to ensure accuracy over the long term is to perform maintenance as required.

Begin with Traceable Standards

Often, it is best to use a traceable standard when calibrating equipment. This means using measurements associated with known national standards. By adhering to the standards set forth by an industry organization, each business knows they are operating within the same level of accuracy and, when applicable, providing similar outputs to customers.

Understand Your Standard

Before calibrating a positive displacement flow meter, it is best to aim for an end result that is at a higher standard than you actually need to achieve. By looking to reach an accuracy of approximately four times the level required based on the unit under test, you can lower the frequency at which calibration needs to be repeated. It also confirms your output is safely within an acceptable range which is critical when dispensing products for customers.

The Need for a Steady State

Calibrating the rate of flow of a fluid through a flow meter requires the materials to pass through at a steady rate. Since calibration is completed in real-time based on the experience rate of output being compared to a known standard, fluctuations in the flow rate will make the task more challenging. By selecting a specific flow rate, the process is simplified as it removes an inconsistency from the equation.

Additionally, using a varying rate of flow may lead to an incorrect calibration. This means that, even when the steps are complete, the associated operations may not be meeting the required standards.

Simultaneous Testing

When measuring the flow rate for the purpose of calibrating a positive displacement flow meter, it is important to use the known standard device simultaneously with the one being calibrated. This method reduces the impact of certain variables that may shift over time. For example, the temperature of a fluid can affect its viscosity. This changes the rate at which the fluid will flow through the positive displacement flow meter and can affect the accuracy of the results.

However, when simultaneous operations aren’t possible, it may be able to be accomplished by using both positive displacement flow meters within a short time, but the results may be less accurate when compared to the other method.

Calibrate Under Standard Operating Conditions

Another component of the calibration process that can increase the accuracy of the end result involves performing the actions in circumstances that mimic standard operating conditions. Flow meters will experience the vast majority of their use during situations that are present during daily operations. By copying the environmental conditions present during those times, you can measure accuracy during the calibration process based on business norms.

Certain factors can have a major impact on flow rates of liquids, such as relative humidity and ambient temperature, so calibrating conditions should mirror those typically present. Additionally, if other mechanical operations or measuring equipment are normally in use in the area, these should be operating during positive displacement flow meter calibrations as well.

Importance of Proper Calibration for Product Sales

A common use of a flow meter is to ensure the proper amount of product is dispensed to customers. Improperly calibrating the positive displacement flow meters involved in these situations means the output does not match what has been purchased. Inaccurate high readings mean the amount of fluid provided during a sale may actually be less than what was purchased, resulting in customers being shortchanged during the transaction. Over time, this can lead to a poor business reputation.

If overly low readings occur, the output will exceed the amount purchased. This means the business is losing profit since the product is being sent out the door even though it wasn’t purchased.

Poor Calibration and Safety

Since flow meters are used in certain mechanical processes, such as in combustion engines, failing to properly monitor the rate of flow can actually present a danger. Following the engine example, inaccurate readings regarding fuel output can result in engine failure or damage. And, should an engine fail while it is in operation, any person in the vicinity may be harmed.

Even in cases where damage to the side is the only byproduct, it could increase the frequency at which maintenance must be performed as well as how quickly the equipment must be replaced. Overall, this leads to increased expenses and decreased efficiency.

When to Calibrate a Positive Displacement Flow Meter

Most positive displacement flow meters are designed to be calibrated on a specific schedule. Generally, this information is provided by the manufacturer to ensure the accuracy of their products. However, in cases where it is obvious the readings are no longer accurate, calibration should be completed at that time instead of waiting for the next scheduled maintenance point. That way, your equipment, and your business can operate at peak efficiency at all times.

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