In the most basic and literal view, a pressure sensor is any device that reacts to a physical force in a manner that is of significance to someone. As an example, one of the simplest types of pressure sensor is the old analog weight scale that uses springs that are machined to exhibit known values of resistance. When a person stands on the scale, springs inside the scale are either depressed or stretched a certain distance. The springs apply force to a wheel that's marked off in calibration units that represent weight values, i.e., pounds (lbs.), ounces (oz.), grams (g), milligrams (mg), etc. As the springs react to the pressure the wheel turns until the springs stabilize. Weight value is then read from the wheel, indicated by a marker line or needle.
You could consider a spring to be a bidirectional pressure sensor since it can react by either stretching or compressing. Springs in a car, a.k.a. shock absorbers, compress and decompress upon impact of a bump or pot hole. Depending on the type of car one is driving, the driver and passengers' derrières may be secondary, readout devices.
Another similar example is the springs in a floating tremolo system on an electric guitar. The player can compress or stretch the springs, thereby lowering and raising, respectively, the pitch of the strings.
However, the pressure sensors electronics engineers and designers work with today are far more sophisticated, even in their simplest forms. More often than not, applications employing these components require accurate if not precision measurements such as medical, military, aeronautical, space, and environmental monitoring. And there is no shortage of parameters, specs, and concerns involved in the proper use of pressure sensors
Pressure Sensor Apps and Challenges
One could take pressure sensors as being the most fundamental of sensor components. Currently, what are the most challenging applications for pressure sensors in general?
Jim Knutti, President and CEO of Acuity, Inc., believes consumer markets are the latest "shiny new thing" in the pressure sensor business. But, according to Jim, "we have seen this herd mentality in the past, chasing the latest "killer app" – engine control, medical disposables, tire pressures, etc. And the MEMS industry in general has had this affliction – witness the optical MEMS "era". These as well as the mobile products are in the phase where the challenges become evolutionary and the space has a few dominant leaders and a lot of wannabes with limited prospects."
Jim views the "real challenges" as "opportunities in applications that are not fully identified, where the technology can be leveraged to create new markets like the aforementioned applications were a number of years ago. We supplied tire sensors in the early 80s, market matured 15 years later, we supplied the first mobile pressure sensors for athletic monitors, bicycles, and ski-monitors in the early 1990s. Most of these markets took several years to develop into strong applications with a few dominant suppliers in each specialty."
Jim claims, "I see the most challenges in emerging segments with an initial teaching sub-segment with a high value added. Examples would be in automated manufacturing, process engineering and energy efficiency controls."
Greg Montrose, Marketing Manager at American Sensor Technologies, Inc. sees materials for pressure-sensor manufacture, increasing pressure levels that need to be measured, and accuracy levels as the prime sources for concern. "There is a limit to the types of materials from which many manufacturers can manufacture a pressure sensing element, leading to difficulty with the measurement of corrosive liquids and gases", he states. "Typically, isolating diaphragms are incorporated into systems, but the added cost and size makes it challenging for system integrators to incorporate pressure transducers."
Greg points out that, "ultra-high pressures are challenging for many pressure sensor materials as the strain required to generate an output signal can be so great that it is close to the yield point in the metal. The number of sensor manufacturers drops off at 10,000 PSI, with even fewer capable of producing pressure sensors above 30,000 PSI."
He also points to "semiconductor processing as becoming more and more specialized and competitive. With decreases in electronic component cost and the reduction in overall component sizes, sensors need to be more accurate and reliable than ever before."
Eric Anderson, Honeywell's Pressure and Magnetic Sensors Product Line Manager, fingers commercial air data, low-speed air data, and industrial process measurement as prime challengers Straying a bit, Honeywell Sensing and Control's Senior Global Product Marketing Manager, Ketan Mehta adds matching product performance with customer price targets, aerospace/military, barometric pressure sensing, and both high- and low-pressure apps as being star contenders.
Eric Anderson states, "Pressure sensors used in providing air data for commercial aircraft need tight accuracy and extreme stability to meet the needs of the customer over the 20 year life of an aircraft. Low speed air data, and low altitude measurements, require extremely precise measurement of pressure changes not conducive to long term stability or robust design
On the industrial-process side, Eric says, "the media isolated sensors used in industrial process measurement take a lot of punishment and require a lot of support equipment to properly function. There is room for improvement here."
Ketan Mehta singles out the pressure sensors used for refrigeration, oxygen delivery, cabin pressure, fuel management and propulsion, and optics in aerospace/military apps. Ketan adds, "Applications are seeing an extended range of operating temperature requirements. Customers are asking for +175ºC at the upper limit, as compared to the past, when +125ºC was usual."
"Measuring low pressures while maintaining sensor performance, like stability, accuracy, resolution" Mehta says, "and applications involving high pressure, high temperature with corrosive media, such as down-hole oil drilling, for example."
A Pattern Forming
Although the applications considered as the most challenging are diverse amongst the front liners, there is a common thread. That commonality is the market's entering the realm of upper and lower extremes, requiring pressure sensors to handle both higher and lower pressures, temperatures, and other parameters.
Similarly, Nader Najafi, President and CEO of Integrated Sensing Systems Inc., takes a slight application detour, "For implantable medical devices biocompatibility is an important issue." Then pointing to expanding parameters, Nader states, "many emerging industrial applications also demand better corrosion resistant features."
Getting straight to the point, Dale Gee, Senior Product Manager at GE, Measurement & Control, believes the three most challenging applications for pressure sensors in general are of the low-pressure, on engine/injection control pressure (ICP), and down-hole drilling variety. Equally direct, yet adhering to the pattern of application divergence, Scott Dalgleish, Chief Operating Officer at Phase IV Engineering claims intrinsically safe, truly-wireless (no wired power to the sensor), and miniature embedded sensor applications as the current gauntlets for pressure sensors. And diverging a bit more, the folks at Sensor Platforms Inc. cite indoor navigation, sports training/fitness monitoring, and medical markets as offering the most challenges.
Kyle Horsman, Product Specialist at TURCK Inc. sums things up nicely while affirming the pattern of diverse apps faced with similar extremes. "The biggest application challenge that we see issues with are those in which pressure spikes occur. Extreme temperatures, such as high heat or even steam, along with possible condensation or even freezing conditions seem to be a constant headache." Kyle continues, "The third is a little broader, but that is in relation to the media being sensed itself. This could be due to a corrosive composition, the possibility for debris or even the way it heats and cools."
Summary of Sorts
From part one of the survey, pressure-sensor makers cite a variety of applications as presenting the most challenges:
- Consumer markets
- Automated manufacturing
- Process engineering
- Energy-efficiency controls
- Sensor materials
- Ultra-high and -low pressure measurement
- Sensor accuracy
- Aircraft data, military, and aerospace
- Medical devices
- Intrinsically safe
- True-wireless sensing
- Embedded sensors
The one thing they all seem to agree on is that parameters of pressure-sensor capabilities are expanding. Higher and lower extremes of pressure need to be measured while the components need to withstand the upper and lower extremes of temperature and other environmental factors.
In part two, we take a look at what the makers see as the three biggest markets for pressure sensors. You may or may not be surprised, but either way, let's see if you agree. ~MD
ABOUT THE AUTHOR
Mat Dirjish is Executive Editor of Sensors magazine. He can be reached at [email protected]estex.com.