Sensors and Actuators


Making sense of the millions of sensors

If there is one industry which is flourishing in modern times it is within the manufacture of sensors and actuators. We may live in the digital age but at some point we will need to measure analogous data, whether X-axis, Y-axis, Z-axis positions, temperature, humidity, Ph, salinity, distance, time and the list goes on. If a microphone is a sensing tool then we can see the loudspeaker motor circuit, the voice coil and magnet as being an actuator of sorts. The core rationale behind this would be a circuit, possibly a closed feedback loop, an audio amplifier, pushing the loudspeaker cone out synchronized with pressure acting on the diaphragm of a dynamic microphone. In this case the magnitude of excursion is the result of amplification factor from input to output.  The result here is done through an analogue process.

IR Sensor
Infra Red Sensor Transmitter

The microphone makes a good example of a sensor which could be used in the measurement of the Decibel. If the output of the amplifier were to be rectified and sent through a switching circuit designed to activate a relay at a preset voltage level, it could be used to warn workers that their working environment was conducive to hearing damage.  In practice this circuit would be used to switch on home lighting when a person performs a hand clap, a rather popular circuit in the 1970s and now seen as gimmicky.


Sensors are used in our everyday lives, from the time we open the door of a car or house to toasting bread, fridge temperature and maintaining aircraft altitude, speed and direction.  In mission critical systems computing systems rely on data from hundreds of sensors, many duplicated for redundancy and reliability and all designed for a specific purpose. As of present motor vehicles do not necessarily have back-up systems except in braking but this is changing. Even with all this technology many vehicles on the road still do not even have a means to tell the driver whether a tail light / brake bulb has failed.  For the casual reader an article on sensors and activators may seem rather ho-hum but in reality they play a vital role in how we use technology. In many instances we have had the technology to get a result but it gets shelved until such time a sensor can be made to work, and work reliably.

A typical example of this would be cameras, consumer or CCTV surveillance. Low light technology has improved in leaps and bounds over the last 10 years but yet is nowhere as good as where it should be. Doing a search on Google to find out the most common problem in modern cars will always return a sensor problem. Yes, they are reliable but the interesting fact is that even with modern technology, we use old technology to determine which sensor is bad. Very few car engine electronic control units return the exact cause of failure yet one faulty sensor can cause the entire engine to become a useless lump of aluminum.  Sensors are not only used in industries which affect our everyday lives however.


Every year technologists, engineers and scientists gather at sensor and activator symposiums, ICSTs (International Conference of Sensor Technology) and other advanced fields which recognize the importance of sensing in electronics and electrical circuits. Green energy and e-Agriculture two fast growing sectors rely on data input to improve efficiency, one to get maximum yield from as little light or wind and the other, crop yield. An interesting study on solar energy revealed that many PV cells have been placed incorrectly on domestic dwellings. Like an audio enthusiast would ensure that the acoustics are 100% in his or her audio room through tests using sophisticated equipment one would have thought that a proper test would be conducted to get maximum yield from the sun.  One should rely on the winter sun and not always readily available energy. This just did not happen. Now, with a more commonsensical way of doing things hopefully engineers and architects will start redesigning our modern human caves to be more in line with modern energy requirements and not necessarily the looks of a house. Sensing circuits play a vital role in this – statistical data: wind speed, wind direction, sun altitude, temp, snow, rain – all at different times of the day, week and year.

Sensors, and quoting from Wiki “is sensitive to the measured property, is insensitive to any other property likely to be encountered in its application and does not influence the measured property.” Although this more or less sums it up, wiring and electronic circuit performance plays a very important role, usually through placement (altitude, vibration, air, sea etc), temperature ambience, noise (and noise temperature), soldering type, shock etc. Input through sensing needs to be critically tested and not just those used in the medical and space/aviation sectors.

As with sensors, actuating mechanisms need to be evaluated within the working environment. Something as simple as a starter motor solenoid has been known to fail in certain brands because of the above norm temperatures encountered. (exhaust manifold springs to mind). Although the electronics used in many “feedback” systems has proven to be reliable, actuators have been known to fail under harsh conditions, the aviation and maritime industries especially.

Volcanic ash is a typical example of an extreme condition; acidic, clogging and a fairly good electrical conductor in large amounts, enough to create a flashover.  Early warning systems for volcanoes, tsunamis, tonadoes, hurricanes all use an array of sensing devices, the actuators driving circuits to propagate information through radio or fixed lines. These sensors and actuators can supply us with all the data we need but we still rely on fast and ready computation. The MH370 wreckage is believed to be somewhere around Reunion yet no radar or radar system picked up enough data to pinpoint it’s movement.  This was not a small aircraft, radar systems are extremely sophisticated compared to those used during WW2 but yet we were oblivious to it’s movement. Or were we? More about radar engineering and aperture sensors here.

Robotics make extensive use of sensing devices and actuators. Automation in the factory, conveyor belts, hoists and lifts, servo feedback, biometrics, microwave ovens, kettles and cookers, even the most primitive type rely on data input to operate correctly and safely.

The more critical the application, the more expensive the sensor. So we go with the normal train of thought but yet interestingly enough, from GPS co-ordinates, re-routing of traffic and climatic conditions, smartphone data is playing a vital role in this. Smartphones are becoming more equipped with sensors which allow the user to get direction, g-force, SPL and a host of combinations which are not lost in the scientific world. Already car manufacturers have apps which connect to the smart phone for monitoring the dozens of computers on board the vehicle. TomTom and Garmin not to be outdone by the Smartphone GPS receiver are directing their resources into health.  Data can be sent to a central medical call-center which can detect problems in blood pressure and breathing of listed patients, the IoT will make this easier.

All because of sensors.