How Does a Pressure Transducer Work?

Pressure transducers are necessary for many industries. They measure pressure and create an electrical output proportional to the input. But with several different types of available models and many uses, it may be challenging to know how to choose the right model for your purposes. This guide will take you through what transducers are, how they work, the different types and potential applications.

What Is a Pressure Transducer?

A pressure transducer, sometimes referred to as a transmitter, is a device that turns pressure into an equally proportional electrical signal. Transducers use variable pressure sensors to measure deflection and resistance. The produced signal will be either a voltage, current or frequency, based on the applied pressure. Most types also require an electrical input, also called excitation. Transducers typically produce one of three types of output — millivolt (mV), voltage (V) and milliampere (mA).

How Does a Pressure Transducer Work?

The majority of transducers have a pressure-sensitive element that reacts to pressure entering through the transducer’s pressure port. As the sensing element or diaphragm is deflected due to the pressure’s force, it moves in relation to a resistor or capacitor plate. This, in turn, sends an output signal that is determined by the varying tension between the input signal, diaphragm position and core resistance.

There are three main types of transducer:

• Potentiometric pressure transducer: Potentiometric sensors are comprised of a precise potentiometer with an arm attached to a Bourdon or bellows. As the arm moves across the potentiometer, it converts the deflection into a measurement of resistance. The nature of these transducers allows them to be small in size and to work in tight spaces. They also produce a strong output, making them excellent for applications with low power.
• Capacitance pressure transducer: Capacitance sensors are sensitive and responsive, using a diaphragm transducer model to measure resistance. The diaphragm has a small space to travel, which means they work well in applications with low differential and absolute pressures.
• Resonant wire pressure transducer: Resonant wire transducers measure pressure with a wire attached to the sensor diaphragm. As the wire oscillates, pressure changes affect its tension, changing the frequency at which the wire is resonating. It results in exact measurements, and the transducer works well for applications with low differential pressures.

Depending on the model, transducers have a range of pressures they can measure and convert with accuracy. They operate best at between 50% and 60% of their maximum rated pressure. So, for a system operating at about 2,500 to 3,000 pounds per square inch (psi), a 5,000 psi rated transducer would work well.

Can External Factors Impact Pressure Transducers?

While most transducers are designed to produce a linear output in relation to the pressures they encounter, certain external variables can have an impact on their output signals. Nothing affects transducers more than temperature. That’s why almost all transducers are manufactured to be functionally accurate within a given temperature range. This sensitivity is due to the fact that as temperatures increase or decrease, there’s a resulting expansion or contraction in fluids and materials, which can change both the transducer’s mechanical and electrical properties and alter its calibration.

They also have a sensitivity to electromagnetic interference (EMI). If there are high field strengths present, it may change the pressure transducer’s electrical output. Fields strong enough to saturate the internal amplifiers can cause the transducer to produce inaccurate outputs, regardless of the amount of pressure. You can measure for external EMI and solve interference issues through shielding, grounding and routing techniques.

Different Types of Electrical Outputs

Pressure transducers are often differentiated by the electrical signal they create. There are three main types of available electrical output:

• Millivolt output transducers: The most economical choice of the three, mV transducers have a low electrical output. The exact output depends on the excitation levels. Since they have a low output signal, they’re susceptible to external electrical noise, making them better for non-industrial environments.
• Voltage output transducers: If you need a higher output level, consider voltage transducers. The actual output will depend on the model, but it is less dependent on excitation levels. Voltage output transducers are less affected by external electric sources, so they’re better for industrial environments.
• 4-20mA output transducers: Also known as pressure transmitters, the 4-20mA transducers produce a strong signal and can transmit them over long distances. They’re the least prone to electrical interference.

Pressure Transducer Applications

The types of transducers and their applications are as varied as the many industries that employ them. Four factors help determine which type of pressure transducer or transmitter needs to be installed in any given system:

1. The particular device (e.g., programmable controller, microprocessor, panel meter) to which the transducer will be sending its output signal.
2. The amount of EMI (electromagnetic interference) that will be encountered, such as in welding, power line and motor applications.
3. The overall distance from the original pressure measurement and output signal to the device that will eventually receive the signal. Note: Transducers are the optimum choice for shorter distances, while transmitters are typically used in applications requiring sending signals over longer distances.
4. The cost of the overall system and its installation.

Transducers are necessary for HVAC compressors and filtering, robotics and automation equipment, industrial transport and lifts, hydraulic feedback in weighing/scale systems and heavy-duty vehicles and power plants and fluid fuel systems.

Trust SEMCOR Transducer Supply

When it comes to expert advice on transducers, a large inventory, prompt delivery and superior technical support, look no further than SEMCOR. We’re your leading supplier of pressure transducers and transmitters from top manufacturers you can trust. Contact our sales and service staff for more product information and answers to all of your questions.