Jochen Schiffner, Industrial Field Application Engineer, Bourns, Inc.
Electronic components have found their way into many mechanical applications. Mechanical designs previously used multiple modules to manage multiple functions or used simple electrical controls such as switches. Now, these applications are becoming increasingly complex. Adding to their complexity, users also expect improved switch functionality, greater system efficiency and smarter and more sensitive operational controls, which have led developers to seek out more advanced component solutions. Component miniaturization, higher levels of integration as well as sophisticated sensor technologies have evolved to meet these requirements.
Specifically, new precision pressure sensors are available as replacements for less accurate pressure switches in, for example, thermal cycling processes to improve efficiency and to allow further system automation. For a wide range of industrial applications in areas such as energy, heavy equipment, transportation, food & beverage or in certain medical environments there is a need to integrate pressure sensors.
A key consideration for selecting the right pressure sensor for these applications and many more is that they must frequently operate in severe conditions where dust, chemicals, shock and vibration and temperature all threaten performance, reliability and longevity. There are many industrial applications where aggressive cleaning solvents at elevated temperatures are used or employ an oil pressure sensor integrated into an electronic control unit. These are the types of applications that require sensors that meet demanding specifications in terms of media compatibility, temperature range and package size.
But what should a designer look for in terms of a sensor’s structure and features to ensure it can handle extreme conditions?
Determining Pressure Sensor Requirements
Sensors have become one of the most critical elements of information collection. Enhanced decision making from real-time data analytics is a major driver in the evolution of sensors and sensor networks. Self-diagnostics, network compatibility, small form factor designs and integrated signal conditioning are considered essential sensor features for new applications.
Pressure sensors work by converting the pressure of the air, gas or liquid they are exposed to into an electrical signal. When evaluating pressure sensors, there are a couple of important attributes to be judged. The pressure range of the sensor and its media compatibility compared to the application’s pressure measurement and feedback needs are a first consideration. Pressure sensor accuracy is another important performance feature to review. Package size and power consumption are also critical in many space-constrained applications.
Currently many applications use bulky mechanical pressure switches or stainless steel and ceramic pressure transducers in robust and large-scale housings to be mounted with threads into pipes or manifolds. And, the large majority of PCB-mount sensors offered today are designed with limited harsh media capabilities. Their resistance is often limited to dry gases or non-aggressive liquids, with narrowly calibrated temperature and pressure ranges.
These sensor solutions no longer match design specifications. Their size and form factor, limited functionally, harsh media resistance and inadequate performance simply do not satisfy next-generation application requirements.
Meeting Next-Gen Sensing Needs
A new generation of pressure sensors is available that combines a small form factor PCB-mount package together with technologies and features to capably handle wide temperature ranges with proven harsh media/chemical resistance. The advanced technologies incorporated also allow cutting-edge technology sensors to support increased integration levels to deliver increased functionality in today’s more complex applications.
There have been a number of sensor design innovations. Electrical output, accuracy and extended environmental operation are key advancements. These technology improvements have also led to greater stability and repeatability of pressure sensor responsiveness.
Pressure sensors that deliver a combination of harsh media compatibility, wide temperature and can handle a high-pressure range all in a single small form factor device offers an ideal solution for most developers.
This level of integration makes new pressure sensor technologies much more attractive for applications that could previously only use media isolated pressure sensors in large and costly packages.
The construction of the sensor is important. Designs based on an adhesive-free die attach mounting process using a eutectic die bond on ceramic results in a robust device structure capable of handling high pressure ranges even at high temperatures. Another advantage of an adhesive-free design is when it can be combined with backside pressure measurement that enables construction with a small number of media-resistive wetted materials. Backside sensing is a type of pressure sensor design whereby the measured media only touches the backside of the measurement element. A distinct sensor accuracy benefit is that all electronic components and other sensitive surfaces are automatically isolated from the media. Wetted materials are all materials in contact with the measured media, therefore, the wetted materials are most critical in terms of media resistivity of the sensor.
For example, the Bourns BPS130 family of pressure sensors are constructed using only inert silicon, glass, Au/Sn and ceramic materials, which are resistant to many aggressive liquids and gases.
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Figure 2. The basic construction of the Bourns BPS130 pressure sensor along with a list of used wetted materials
Key pressure sensor features that deliver design benefits:
Reliability in Harsh Pressure Sensing Environments
Additional applications for pressure sensors will continue to grow as developers realize the benefits of converting more expensive and larger mechanical pressure sensors to lower-cost, small form factor devices. Technology advancements contribute to increased sensor accuracy, sensitivity and long-term reliability that will expand their usage.
Today’s advanced pressure sensor construction and features give designers the component miniaturization and higher integration required to enable enhanced switch functionality, higher system efficiency and accurate electronic operational controls. They have also evolved providing the ability to measure pressure even of liquids in demanding or extreme environmental applications.
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Figure 3. Examples of pressure sensors
A further advantage of new construction techniques is it is now possible to integrate the measurement functionality of stainless steel and media-isolated pressure sensors at the PCB level. This leap forward in design brings measurement functions and additional value into designs that were either impossible or very difficult to supply in the past.
By giving more functions to the PCB or into one housing, today’s pressure sensors contribute to reduced wiring complexity, lessen the risk of signal distortion because of environmental noise and also help decrease the number of sealed electrical connections. All important features and benefits to consider when selecting the right pressure sensor for a new harsh media application.