What Are Pressure Transducers & Fill Materials: A Closer Look

What are pressure transducers?

Let’s answer another question first: what are transducers?

A transducer is a device that can convert one form of energy into another. In everyday applications, transducers are used in electronics from microphones to thermometers, but in the world of manufacturing and other large-scale non-commercial applications, different types of transducers are used to perform a variety of different sensitive tasks. 

Pressure transducers are one common type; they may be small, but their uses are varied, and their purpose is vital to many different industries. Using a combination of electrical and mechanical components, pressure transducers are specifically designed to measure and monitor changes in pressure in a wide range of industrial systems. These range from food and pharmaceutical plants, hydraulics, and HVAC equipment, to water treatment, industrial machines and more. 

How do Pressure Transducers Work?

Pressure transducers connect to a device producing air pressure, usually to the transducer’s “pressure port”. Upon entering the transducer through the pressure port, that pressure is deflected through an internal diaphragm within the transducer. 

Once this occurs, gauges located on the diaphragm indicate how much strain of movement is being caused by the pressure, which is then amplified and conditioned by the transducer’s circuit board. Finally, as a result of this process, an electrical signal is generated, and the nature of that signal indicates the amount of pressure measured. 

This activity occurs constantly within a pressure transducer, meaning they are a constant monitor of pressure that can respond to even sudden changes in real-time. 

Pressure transducers are mainly used in industrial applications and subject to extreme heat and cold. To withstand these conditions, they are specially engineered to prevent shock, vibration, and severe temperature factors from damaging their internal components or interfering with their monitoring process. Because of this reliability, pressure transducers can be found in nearly any application that relies on constant pressure monitoring. 

Types of Pressure that Transducers Can Measure 

In applications like maintaining an isolation room, it’s extremely important for transducers to give completely accurate pressure readings. However, since many factors could potentially contribute to receiving inaccurate readings, other less-crucial applications can afford for a transducer to have only moderate accuracy. 

Accuracy is largely determined by the Transducer’s built-in sensor equipment. Regardless, these types of pressure should be detected and displayed with a reasonable degree of accuracy by many different types of transducers. 

True to their name, pressure transducers are designed to measure and detect changes in pressure, and there are three main types of pressure they can detect.

• Absolute Pressure: This type of pressure is unique in that it’s only experienced when air is completely absent from a space, and detecting this type of pressure is how you can be certain a perfect vacuum has been created. When this type of pressure is measured, it will stay completely consistent and cannot fluctuate.
• Gauge Pressure: Pressure measured against the local atmospheric pressure of a given area, like a tire pressure gauge Gauge pressure transducers use local atmospheric pressure as a reference to measure any positive pressure greater than the local atmospheric pressure level.
• Differential Pressure: The difference in levels between two applied pressures. Transducers detecting this compare two different pressure levels to find the level of difference between them, as opposed to using atmospheric pressure as a control to judge changes in pressure. These transducers usually have two pressure ports instead of one, one that accepts high pressure and one for low pressure.

What Are Fill Materials?

Pressure transducers convert energy from one form to another, like converting pressure into an electrical signal. But in order to do this, transducers are filled with a liquid solution that creates the pressure. This fluid exerts pressure on the metal diaphragm located at the tip of the transducer’s sensor; the sensor detects that pressure, beginning the conversion process. 

Depending on what a transducer is going to be used for, and in what application, different liquids are used as the fill material. Each liquid comes with benefits and drawbacks that make them the ideal choice for specific applications. 

There are three main considerations that should be made to ensure the right fill material is used for the job:

• Compressibility: The compressibility of the fill material liquid should be capable of achieving the maximum pressure range of the transducer. 
• Thermal Expansion Coefficient: Every liquid has what is called its “Thermal Expansion Coefficient”. This is the minimum temperature where the liquid starts to expand when subjected to extreme heat. Fill materials should have a high thermal expansion coefficient to prevent them from expanding in applications that need high temperatures. 
• Operating Temperature: Every liquid has a temperature limit, and exceeding that temperature causes it to boil or break down. If this limit is below the operating temperature range, the fill material should not be used. 

Mercury and Other Types of Fill Materials

Mercury is the most popular type of fill material, especially for extrusion and other high-temperature applications. Mercury is almost always used because it does not display significant thermal expansion under widely used operating temperatures, and it is capable of remaining a liquid at almost any temperature. When other liquids could freeze or evaporate, mercury remains in its liquid state from below freezing to upwards of 350 degrees Celsius (662F).

However, mercury has one major limitation – it is highly toxic. So toxic, in fact, that other fill liquids are safer alternatives, but none perform as well as mercury in extreme temperatures. 

Other commonly used types of fill materials include:

• Oil: Unlike mercury, oil is a non-toxic liquid generally regarded as safe (GRAS) by the USFDA. Oil can be used at moderate operating temperatures, but anything too high can cause it to degrade as it is an organic substance. 
• NaK: NaK has also been declared non-toxic by the USFDA. It is a liquid-metal alloy made of sodium and potassium. Unlike oil, NaK can be used at high operating temperatures, but it can explode when it comes into contact with air. NaK can only be used in FM explosion-proof areas. 
• Vertex Sensing: Vertex sensors perform what is called “capacitive sensing”, meaning they do not use a liquid fill material. Available for pressure from 250-10,000 PSI, vertex sensors are highly accurate and do not present the waste byproducts of mercury or oil. In many cases, Vertex sensing is more accurate than using mercury. 

Dynamic Electronics: Factory-Direct Industrial Products

Pressure transducers are an integral part of maintaining many industrial processes, and they’re an indispensable component for numerous industries around the world. If you’d like to learn more, explore our wide range of transducers, or contact us today to find your custom solution.