Pressure Sensor Features Required for Harsh Environments
Electronic components are now included in many mechanical applications. The driving factors for this migration are due to the increasing complexity of mechanical designs coupled with user expectations for increased functionality. Mechanical applications that once employed multiple modules to manage multiple functions or used simple electrical controls such as switches are no longer sufficient in meeting sophisticated feature requirements.
The good news is that electronic component technologies have advanced with features and capabilities allowing designers to meet market demands for improved switch functionality, greater system efficiency, and smarter and more sensitive operational controls. Continued innovations in component miniaturization, higher levels of integration as well as next-generation sensor technologies have evolved to meet these requirements.
For instance, there are new precision pressure sensors that have been proven to be ideal replacements for less accurate pressure switches in, for example, thermal cycling processes. These processes benefit from the latest pressure sensor technologies that provide the ability to improve efficiency and facilitate additional system automation. In general, pressure sensors are becoming necessary components to enhance safety, energy efficiency and process control/productivity in a large variety of industrial applications including energy, heavy equipment, transportation, food & beverage or in certain medical environments.
Simply adding a pressure sensor to a design is not always a straightforward decision. The Challenge for designers is that applications must frequently operate in severe conditions where dust, chemicals, shock and vibration and temperature all threaten performance, reliability, and longevity. Plus, 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.
Therefore, key considerations for selecting the right pressure sensor for these applications is that they meet demanding specifications in terms of harsh 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?
Meeting Application 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 the 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, lack of harsh media resistance and inadequate performance cannot satisfy next-generation application requirements.
Advanced Sensor Features
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 sensors to support increased integration levels to deliver increased functionality in today’s more complex applications.
A prime example is sensors based on MEMS (Micro-electro-mechanical Systems). MEMS pressure sensors use cutting-edge technology to convert measured mechanical signals into electrical signals. MEMS sensors have proven high performance as compared to similar sensors based on competing technologies. MEMS sensors are manufactured using macro-level machining that produces high precision, highly sensitive sensors. Small size, lower cost, and reduced power consumption are also contributing to the usage growth of MEMS-based sensors.
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 offer an ideal solution for most developers.
Figure 1 illustrates the compact sensor dimensions that are available today.
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® Model BPS130 and BPS140 families of pressure sensors are constructed using only inert silicon, glass, Au/Sn (BPS130 only) and ceramic materials, which are resistant to many aggressive liquids and gases.
Figure 2 shows the basic construction of Bourns BPS130 and BPS140 pressure sensors along with a list of used wetted materials.
Key features of the Bourns BPS130 and BPS140 pressure sensors offer significant design benefits:
- High-pressure sensing: 15 PSI to 500 PSI (1 bar to 34.5 bar)
- Extreme sensitivity and stability: Total Error Band of 2.5 % FS over a temperature range of –40 °C to 150 °C (Six-Sigma process)
- Lifetime drift: 0.5 % FS
- Media compatibility: harsh (air, liquid & gas)
- Compensated analog output
- Absolute and gauge options
- RoHS and REACH compliant**
Growing Need for Harsh Environmental Sensors
New applications that can use pressure sensors are expected to grow as developers realize the benefits of converting more expensive and larger mechanical pressure sensors to lower-cost, small form factor devices. Growth will also be attributed to technological advancements that make increased sensor accuracy, sensitivity and long-term reliability possible.
Demonstrated by the unique construction and features offered in Bourns® Model BPS130 and BPS140 pressure sensors, designers not only can get a solution that follows the trend of miniaturization and higher integration of electronics but also one that can measure the pressure of liquids in demanding or extreme environmental applications.
The Model BPS130 and BPS140 pressure sensor lines feature harsh media compatibility and high-temperature operation with high accuracy. These sensor models offer particularly stable performance over the product’s lifespan, and the ability to work with a wide range of pressures.
In addition, new construction techniques now make it 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.