Feature Sensing Technology
Keeping control & taking measure
Holger Morgenstern at Conrad Electronics explores the importance of sourcing the right sensors for the rapidly growing market for ever smarter systems
ense and Control must surely be two of the most important key- words for human beings today, as we seek to further improve quality of life while managing our increasing demands on dwindling natural resources. Control is vital to maintain efficient production and manage resources. Without sensing, there can be no control.
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The value of sensors to modern life is already recognised; the total global market for these tiny devices is esti- mated to be significantly more than
€50 billion, and there is strong annual growth in sectors such as gas sensors,
distance sensors and humidity sensors. Choosing the right sensor for a given task may seem straightforward, but in practice can sometimes be quite com- plex. Often, engineers must choose between several different sensing tech- niques, each offering various strengths and presenting a variety of engineering challenges. An example is whether to use position or ultrasound sensing to detect movement. In some instances, a capaci- tive, inductive optical, radar, infrared or even ultrasonic proximity sensor may be better suited to the target application. When the optimum sensor technology has been chosen, factors such as the range and resolution of the sensor must be considered. This can be particu- larly important for movement or position sensing in industrial processes, or for temperature sensing.
Even when these issues are resolved, a voice of experience is often needed. It is important, for example, to select a sensor that will generate the most suit- able output signal, either analogue or digital, and providing an acceptable full-scale analogue voltage range or conforming to a particular transmis- sion standard or protocol. Some indus- trial sensors, such as Panasonic laser distance sensors, for example, are offered with an analogue interface based on voltage or current deviation.
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Mechanical aspects such as physical size or package style also directly influence suitability for use in a given piece of equipment or application. Silicon temperature sensors provide one example: the Infineon KT series for applications between -50°C and 150°C is available in standard or mini TO-92 leaded, SOT-23 surface-mount, or custom panel-mount package options. Platinum temperature sensors, which are available in a variety of package styles and form factors, have a wider sensing range typically -70°C to 500°C and offer specified temperature stability better than 4000ppm/K. The type of mounting, such as bolt- down or clip-mount, can also influence the cost and complexity of the design and the time needed to assemble units in production. Biotech, for example, produces a wide range of flowmeters for various applications, flow-rates or media’s like gas, liquid or aggressive substances. Of course, designers must also take into account any price premi- ums associated with sensors offering the greatest ease of use.
Choosing the right sensor When choosing position or movement sensors, the range, resolution and repeatability are the dominant selec- tion criteria, and typically are more important than absolute accuracy for most applications. At one end of the resolution spectrum, the Sharp GP2Y0AH01 infrared distance meas- urement sensor, which was originally designed to measure the thickness of paper in printers and copiers, can be used for a variety of industrial purposes such as measuring thickness, displace- ment or proximity.
It is capable of measuring displace- ments between 4.5mm and 6.0mm with minimum resolution of 0.1mm, and generates an analogue output voltage proportional to the absolute displacement measurement.
Holger Morgenstern is Product Manager at Conrad Electronics
Figure 1: Moisture and temperature sensor
Figure 2: Radar motion detector
Figure 3:
Inductive proximity switch
On the other hand, the Sharp GP2Y0D02YK long-distance measur- ing sensor provides a digital output which is logically high if the distance to the detected object is between 20cm and the sensor’s fixed threshold of 80cm. If the distance detected is between 80cm and 150cm, the output is held low.
In some types of mechanisms, par- ticularly those that are subject to wear capable of causing inaccuracy – such as when an angular encoder is used to monitor revolutions of a wheel whose circumference progressively dimin- ishes with wear – an auxiliary non- contact sensor such as an optical sensor may be designed-in to enable the system to self-recalibrate. This approach may be taken where equipment is to be used in dusty envi- ronments or in other situations where the risk of obscuring the sensor window could preclude the use of optical sensing as the main position monitoring technique.
Humidity and temperature sensors are among the fastest growing cate- gories, and are widely used to improve the performance, reduce the energy consumption, and enhance the safety of equipment ranging from home appliances and HVAC systems to auto- motive controls and medical devices. Humidity sensors for example are available in a variety of types and form factors, ranging from miniature PCB- mount devices to complete adjustable modules such as the Hygrosens TW2001-C Humidistat. Another option is a combination with humidity and temperature sensor in one solution such as the Sensirion SHT-series. These give high-precision measuring of both values and a digital output for the direct input to a microprocessing unit. Gas sensors, another strongly growing sector of the sensors market, are used for a wide variety of safety, surveil- lance and monitoring applications. Dedicated carbon monoxide detectors may use a single type of sensor, such as the Applied Sensor AS-MLC, which is packaged in a standard TO-39 4-pin header. The Applied Sensor AS-MLx range also includes sensors for nitrogen dioxide and natural gas.
Sensors for ammonia, sulphur diox- ide, methane, butane, hydrogen, ethanol and fuel vapour are available in through-hole PCB-mount packages from a variety of manufacturers. The Figaro TGS2600, on the other hand, is optimised for air-quality and pollution sensing, and has applica- tions in smart-building controls as well as environmental monitoring equipment for purposes ranging from healthcare to town planning. Conrad Electronics
www.conrad-uk.com Enter 211
SEPTEMBER 2013 Electronics
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