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 sensor construction is very simple and robust: Control Engineering diagram.
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.

For more reading on pressure measurement:
Pressure sensor technologies
Understanding pressure instrumentation

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 .

No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Make Big Data and Industrial Internet of Things work for you, 2017 Engineers' Choice Finalists, Avoid control design pitfalls, Managing IIoT processes
Engineering Leaders Under 40; System integration improving packaging operation; Process sensing; PID velocity; Cybersecurity and functional safety
Mobile HMI; PID tuning tips; Mechatronics; Intelligent project management; Cybersecurity in Russia; Engineering education; Road to IANA
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Flexible offshore fire protection; Big Data's impact on operations; Bridging the skills gap; Identifying security risks
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
click me