Variable Capacitance Pressure Sensors

Our partner Setra, was founded in 1967 by brothers Dr.Y.T. Li and Dr. S.Y. Lee, both professors of engineering at the Massachusetts Institute of Technology and co-developers of the variable capacitance transduction principle.

Their philosophy, which is still carried on today and expressed in the Setra mission statement, is that whether you require low price, ruggedness and accuracy for OEM use; or the highest possible accuracy for critical test, quality control or manufacturing applications, Setra’s products should offer you significant improvement in measurement accuracy.

Building on this heritage of innovation, Setra has designed and developed the most comprehensive product lines of pressure sensors in the world. Setra has been innovating Test & Measurement sensor designs for over 50 years and has become a leader in the pressure transducer market.

What is Capacitive Based Pressure Sensing?

Our patented variable capacitance technology is based on all stainless steel micro-tig welded sensors. The radially tensioned diaphragm and insulated electrode form a variable capacitor. This provides the industry-best accuracy for very low pressures and unmatched long-term stability.

Capacitive pressure sensors are expertly designed adaptations of a simple, durable and fundamentally stable device, known as the electrical capacitor.

In a typical Setra configuration, a compact housing contains two closely spaced, parallel, electrically isolated metallic surfaces, one of which is essentially a diaphragm capable of slight flexing under pressure. The diaphragm is constructed of a low-hysteresis material, such as 17-4 PH SS or a proprietary compound of fused glass and ceramic (SetraCeram). These firmly secured surfaces (or plates) are mounted so that any slight physical flexing of the assembly, as a result of applied pressure, alters the gap between them (in effect, creating a variable capacitor). The resulting change in capacitance is detected by a sensitive linear comparator circuit (employing proprietary custom designed ASICs), which amplifies and outputs a proportional, high level signal.

While Setra may be known for variable capacitive transducers, there is another viable pressure sensing technology we use for some industrial and OEM products – thin film/strain gauge.

Types of Capacitance Sensor Designs 

Since Setra was started in 1967, capacitance has been and will continue to be the core technology for their pressure sensor designs. Each of the capacitive sensors that are manufactured employ two closely spaced parallel plates, one of which is fixed, while the other is a flexible diaphragm allowing for flexing when pressure is applied. This straightforward concept, combined with innovative design and world class manufacturing, has enabled Setra to become a leading supplier to industry.
 

Stainless Steel Stretched Membrane

This sensor is designed and manufactured using a stainless steel stretched membrane diaphragm that moves towards a fixed electrode. Setra uses proprietary tension control enabling the sensor to measure extremely low pressure measurements. This configuration also provides up to 100x overpressure capability in the application.

Often accommodates for pressure ranges 0.1" W.C. to 15 PSI. Used for pressure datums differential, gauge and compound.


 

Machined Stainless Steel Sensor

This sensor is designed and manufactured using a machined stainless steel diaphragm that moves away from a fixed electrode. Setra uses proprietary manufacturing techniques to take advantage of the diaphragm’s elastic properties enabling accurate mid to high pressure measurements. This configuration also provides up to 10x overpressure capability in the applications.

Often accommodates pressure ranges 15 PSI to 10,000 PSI. Used for pressure datums gauge, absolute and compound.


 

Ceramic Pressure Sensor

This sensor is designed and manufactured using ceramic material fused together with glass and gold to form the sensing element. The ceramic properties enable superior thermal performance and long term stability when compared to stainless steel or other metallic sensors.

Often accommodates pressure ranges 0 to 100 PSI. Used for pressure datums barometric, gauge and compound.

Please visit our informative blog post for further information on how to understand proof and burst pressures.

Highest Accuracy Pressure Sensors

Setra’s AccuSense™ line of products offers a 0.25% “Total Error Band” specification over a temperature range of -20 to 60°C for each of its transducers. This specification gives the user a more comprehensive look at the sensor’s performance in real world installations.

Total Error Band (%FS) = Accuracy + Zero Offset + Span Offset + Zero Temp Shift + Span Temp Shift

• ASM Single Point High Performance Sensor - is the highest accuracy pressure transducer for measuring gauge, absolute, compound and vacuum pressure in the AccuSense™ product line The ASM’s ±0.05% FS accuracy is calibrated using the “End Point Method” which improves linearity when compared to competitive transducers which use the “Best Fit Straight Line Method” of calibration.
   
• ASL Differential High Performance Sensor - is the highest accuracy pressure transducer for measuring low differential pressure in the AccuSense™ product line. The ASL uses resonant variable capacitance sensor. This sensor is linearized and thermally compensated through a computerised curve fitting algorithm that optimizes the sensors linearity for maximum accuracy in demanding applications.

Advantages of Capacitance Technology

Not all pressure sensors are made to withstand the harsh environments and stringent requirements of the Test & Measurement industry like Setra’s capacitance sensors.
 

• High Accuracy - up to ±0.02% FS for critical measurement tasks.
   
• Low Differential Pressure - as low as 0.1" W.C. typical.
   
• Long Term Stability & Reliability - the capacitance sensing element provides a high level of output that is not only accurate when first purchased, but will remain accurate over the long haul. The stable sensor will prevent the need for constant re-calibrations of the sensor.
   
• High Overpressure and Line Pressure Capabilities - class leading overpressure capabilities, without causing damage to the sensor element.
   
• Rugged Design to Withstand High Shock and Vibration - applications in the Test & Measurement industry are among the most demanding; not only with performance but also with harsh operating environments. These applications have caustic chemicals and high pulsation during testing. Setra’s rugged design prolongs the life of the sensor and keeps you up and running to get the job done.
   
• Application Engineering Support - quality and reliability you can depend on, with all sensor calibrations traceable to NIST standards, backed by an astute team ready to support custom requests for many applications.

Performance in Test & Measurement applications is crucial. The data collected is used to ensure product quality, improve efficiency, and provide public safety. Setra’s sensors have a long history of providing reliable test data with accuracies as high as 0.02% FS.

Custom Pressure Sensor Solutions

You can lean on our highly skilled engineers and technicians to solve your most unique challenges. You can rest assured that when everything is at stake, we will put the right technical team members on the job.

We will first zero in on your target specs and determine if they are achievable. Then we will break down the problem and select the right technology platform for the application. Every aspect of your application’s mechanical, electrical and environmental constraints will be considered. We will then vet controlling variables as materials, enclosure geometries, sealing methods, and manufacturing methods. Once concept engineering is complete we move to prototyping, evaluation, and production using our regimented process model:

• Concept - can it be done? If the answer is yes (and it usually is), we move to platform choice and vetting of engineering options.
   
• Prototype - next, we will work alongside design engineers and manufacturing teams to collaborate on producing a functional prototype, using Setra standard manufacturing approaches wherever possible.
   
• Evaluation - after factory testing, the prototype is sent to you for evaluation and feedback. You send it back and iterations are made until you are fully comfortable that production models of the prototype will drop in perfectly.
   
• Production - documentation is finalised and production associates are trained in preparation for manufacturing a pilot run and first production order.

Test & Measurement Application Examples

Capacitive pressure sensors have earned a reputation for consistently high accuracy and unmatched long-term stability. These sensors are used in many applications where accuracy and repeatability are vital. A few of these include:

• Engine Test Stands - are complex, engineered systems designed to measure, control and record many parameters during new engine development and final verification prior to delivery. Strict legislation has made manufacturers rethink their processes and create new, innovative designs. We offer a wide variety of solutions to fit each pressure application on the engine test stand, empowering designers with the information and ability to ship the best product possible to the end customer.
   
• Pressure Decay Leak Detection - is a critical test conducted to ensure quality material is being processed at each stage of the manufacturing process. Pressure decay leak detection is a trusted method for sensing small leaks in a variety of applications. The differential pressure method enables the system to test for very small leaks in filters and activated IV valves, while the gauge pressure method enables a system to test at higher line pressures with larger leak rates on housings, engine components, etc. We have solutions that offer industry-leading overpressure specifications and high accuracy to exceed the needs of these demanding applications.
   
• Filter Test Stands - are used in multiple applications in a variety of industries. Millions of pounds are spent developing and manufacturing products for the pharmaceutical, chemical, and automotive markets that mandate filtration to meet regulatory or performance requirements. The job of the filter is to reduce particulate matter (PM) from entering or leaving a space, being inhaled by an associate working in a hazardous environment or from entering a critical area of a machine or process. Our products have the ability to accurately measure both low (<1” W.C.) and high (up to 10,000 PSI) test pressure which can aid designers in the development of new filter concepts and performance verification.
   
• Porosimetry & Surface Area Systems - understanding pore size and surface area of any material is critical to producing high quality products. Gas Sorption is a technique used to calculate and measure those characteristics to maximize the effectiveness of the material. This method is based on van der Waals theory of attraction: the sum of attractive forces between molecules other electrostatic or chemical bonds. Our products provide real-time reassure data of varying gas concentrations in the sub-atmospheric environments of the chamber. The results of a gas sorption analysis aid in the design on products across many industries.

HVAC/R and Industrial Solutions

In addition to the test and measurement portfolio, we can also help with HVAC/R and Industrial solutions such as:

• Differential Pressure Sensors - typically for low pressure sensing requirements. Our most popular models include the 267 very low differential pressure sensor, MR1/MR2 multi-range DP sensor, 230/231 true wet-to-wet pressure sensors and 264 low cost differential pressure sensor.
  
  
• Room Status Monitors - including room pressure monitors and environmental controllers. Our most popular models include the LITE visual differential pressure monitor, FLEX environmental monitor and controller and SRPM/SRCM room pressure and condition monitors.
   
• Power Monitors - including our ever-popular Setra Power Meter and supporting accessories, such as Rogowski Coils and Current Transformers.
   
• Gauge Pressure Sensors - for static/single-point pressure measurement. Our most popular models include the AXD industrial pressure transducer, 206 industrial pressure sensor and 256 industrial pressure sensor for data centres.
   
• Relative Humidity - including temperature and RH measuring solutions. Our most popular models include the SRH humidity sensors, available in various mounting formats for different installations. 
   
• Pressure Calibration - for ultra-low pressure measurement and documenting calibration. Our all-in-one MicroCal advanced modular pressure calibrator is a time-tested solution trusted by NASA.

Why Use Setra Solutions?

• Made in the USA
• Industry Leader for 50 Years
• Innovator of the Variable Capacitance Principle
• 5-Sigma Quality Standards
• 95% On-Time Delivery
• 99.8% Quality Rating
• 10+ Million Sensors Shipped (And Counting)

Not sure if these are right for you? For additional information on the types of pressure sensors available on the market, please visit our blog by clicking here.

Need some guidance? Contact our experienced technical team here for application support and advice on components for your system.

For a brief overview of diaphragm deflections, please watch our introductory video below: