Tutorial: Capacitive pressure sensors
Measure pressure: Capacitive sensing offers a broad range of advantages for process instrumentation. See diagram.
When selecting instrumentation technology, the task often comes down to choosing the most favorable selection of characteristics. For pressure measurement, capacitive sensing offers trade-offs that have earned it wide acceptance.
Capacitive pressure sensors use a moving diaphragm and a stationary base as the two capacitor plates. Either the two plates are charged separately, or the diaphragm serves as a bridge across two fixed electrodes. In either case, when the diaphragm deflects due to increasing pressure, the surfaces come closer together and the capacitance value changes. This change can be quantified and converted to an analog or digital output.
Simple construction, 7 more advantages
This approach makes for a very simple mechanism, which is one of the reasons it has been used so widely. Key advantages include:
Wide range of diaphragm materials possible;
Relatively simple electronic signal conversion;
Low power consumption, suitable for battery power;
Correction for ambient and process temperature conditions is uncomplicated;
High degree of accuracy and stability possible;
Sensors can be very durable capable of withstanding heavy overpressure; and
Can be configured for gage, absolute, or differential pressure readings.
There are some downsides to the technology compared to other sensing techniques. The extent of these varies between manufacturers, so consult with your supplier.
Maximum pressure range is relatively low, but within most process application limits;
Operating temperature range is narrow; and
Sensors tend to be comparatively bulky as the diaphragms require specific minimum surface area.
Pressure instrumentation suppliers do not always indicate what the sensing technology is for a given device or family. Moreover, many companies use different technologies for subgroups within a larger line, so you may have to ask for specifics. Capacitive pressure instruments are available from a range of manufacturers, including:
Endress + Hauser
Rosemount (Emerson Process Management)
—Peter Welander, process industries editor, PWelander@cfemedia.com ,
Control Engineering Process Instrumentation & Sensors Monthly
Register here to select your choice of free eNewsletters .
Case Study Database
Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.
These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.
Click here to visit the Case Study Database and upload your case study.
Annual Salary Survey
In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.
Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.