A Quick Guide to Positioners: Types, Applications, and How They Work

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If you work in the process industry or just have an interest in how industrial processes work, you are probably familiar with a positioner, even if you aren’t sure exactly what it does. These instruments are used for valve control, keeping everything running smoothly and precisely. Leading positioner manufacturers in the process industry include Westlock Controls, Flowserve PMV, Emerson and Siemens to name a few. In this blog, we’ll break down the different types of positioners, their applications, and the principles of operation.

 

So, What Exactly Is a Positioner?

A positioner is like the brain of a control valve. It ensures the valve does exactly what it’s told to do by a control signal. Think of it as a translator and enforcer in one. When the control system says, “Open the valve to 50%”, the positioner makes sure it happens — no more, no less.

Furthermore, positioners are particularly important in systems where precision is key. They monitor and adjust the valve position to keep processes running smoothly, even if external conditions, like pressure changes, try to throw things off balance.

A major misconception is that the positioner physically moves the actuator, when in reality it supplies the correct volume of air to allow the actuator to move to the set point.

 

Types of Positioners: Which One Does What?

There are three main types of positioners: pneumatic, electro-pneumatic, and digital. Each one has its own strengths and ideal applications.

Pneumatic Positioners

Pneumatic positioners are the old-school classic of the positioner world. They rely on compressed air to function and don’t require electricity. This makes them a popular choice in hazardous environments where sparks could be dangerous, like chemical plants or oil refineries.

How They Work: Pneumatic positioners receive a pneumatic signal (usually 3-15 psi) from the control system. They compare this signal to the valve’s current position and adjust the airflow to the actuator to correct any mismatch.

Applications: Suitable applications for Pneumatic Positioners are simple, robust operations where electricity is unavailable, and environments with explosion risks.

Electro-Pneumatic Positioners

As the name suggests, electro-pneumatic positioners are a blend of both: electrical control signals and pneumatic valve actuation. They’re more versatile than their pneumatic-only counterparts and can handle more complex tasks.

How They Work: These positioners take an electrical signal (typically 4-20 mA) from the control system, convert it into a pneumatic signal, and then use that to adjust the valve position. They often include additional features like diagnostics and feedback.

Applications: Electro-Pneumatic Positioners are often used in industrial setups with both electrical and pneumatic infrastructure, and processes involving complex control strategies that require higher precision.

Digital Positioners

Digital positioners are the more high-tech members of the group. They’re equipped with microprocessors, allowing them to handle a wide range of tasks, from diagnostics to advanced control algorithms. These positioners are all about precision, efficiency, and connectivity.

How They Work: Digital positioners receive an electrical signal (4-20 mA or digital communication protocols like HART, Foundation Fieldbus, or Profibus). They use their microprocessors to compare the desired position with the actual position and make real-time adjustments. Many Digital Positioners come with self-calibration and remote monitoring capabilities.

Applications: Ideal applications for Digital Positioners are high-precision processes with a focus on automation and data collection, and industries embracing the IoT (Internet of Things).

 

How Do Positioners Work?

No matter the type, all positioners follow the same basic principle:

Signal Reception: The positioner receives a control signal (pneumatic or electrical) from the control system.

Comparison: It checks the valve’s current position using feedback from a sensor or linkage.

Adjustment: If there’s a discrepancy between the desired position and the actual position, the positioner adjusts the actuator to correct it.

Imagine you’re steering a car. If you’re veering off the lane, you adjust the wheel to get back on track. Positioners do the same thing but for valves.

 

Choosing the Right Positioner

When selecting a positioner, it all comes down to your application. Need something reliable in a hazardous environment? Go for a pneumatic model. Want a balance of precision and robustness? Electro-pneumatic is your go-to. Looking for reliable control and connectivity? Digital positioners are the way to go.

Positioners might not be the stars of the show, but they play an important role in making sure everything goes off without a hitch. Whether you’re controlling the flow of chemicals, steam, or even chocolate in a food processing plant, positioners are the operators keeping industry flowing.

Now that you know the ins and outs of different types of positioners, you should have a better understanding of which one is most suitable for your application. Need to purchase a positioner? Visit our Positioners page and browse our range of pneumatic, electro-pneumatic, and digital positioners. Additionally, if you need some advice or guidance on which option to choose, please contact our expert team who are on hand to assist you.

Looking for a Smart Digital Positioner? → Try the Westlock K20 Smart Positioner risk-free with our sale or return promotion, all backed by our exclusive Valve & Process Solutions 5 year warranty. Terms and conditions apply. Contact our team for more information.

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