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There’s a lot to do before taking measurements, including selecting a suitable sensor for the application.
There’s an endless choice of sensors out there, which means picking the right one can be a daunting task. If you don’t work with sensors routinely, things can become even more confusing.
Choosing the right sensor is important, as it will likely impact the performance, production cost, calibration and service of the entire system. Accurate selection will depend on knowledge of the application type, the variable of product and the operating environment conditions.
Sometimes, it’s not so much about selecting the right sensor but about eliminating all the wrong ones.
To help you navigate the world of sensors, we’ve created a guide for determining the right sensor for each job.
Generally speaking, there are two methods for selecting an industrial sensor:
1. Selection by product classification – choosing a product based on characteristics such as sensing method, configuration, installation and other requirements. This requires a more in-depth understanding of the sensor market and how the chosen sensor needs to operate.
2. Selection by application – this object-oriented method requires a thorough understanding of the intended application. If you understand your application needs in general terms such as heat or weight, you’ll already know which sensor types are irrelevant in your search.
Regardless of the method of selection, you can find an appropriate sensor for nearly any application from within these seven common classes of sensor.
Each class of sensor defines a group of devices, and each group has individual species and members. These all have unique operational characteristics and optimal use scenarios. Let’s take a look at each type:
4. Vibration & Inertia
5. Position & Displacement
The most common sensors for temperature measurement are thermocouples, thermistors, non-contact pyrometers and resistance temperature detectors (RTDs). Fibre-optic sensors, while more specialised, are growing in popularity for temperature measurements.
Strain is typically measured using a resistive strain gauge or even with optical camera systems. Strain gauges can measure very small twists, bends, and pulls on surfaces. To put the typical strain gauge sensitivity into context, if you had a 25.39km long rope and stretched it 25mm, that’s equivalent to 1 microstrain or 1ppm change in length. Similar to temperature systems, fibre-optic sensors can be used to measure strain in hazardous environments.
Tilt sensors (also known as inclinometers) measure the slope/angle or tilt of objects based on gravity within various applications. The sensor produces an electrical signal which is proportional to the degree of tilt in multiple axes. Tilt sensor types include single axis with single output, dual axis with dual output, and dual axis with single output. Digital tilt sensors can be combined with GPS for simultaneous measurement of displacement and tilt.
Ceramic piezoelectric vibration sensors (also known as accelerometers) are most commonly used to detect vibration because of their versatility. Inertial measurement units (IMU) measure both linear and angular motion. The two main technologies used in these sensors are MEMS and force-balance. Accelerometers may be single, biaxial or triaxial in type, depending on the specific application and vibration generated. Triaxial accelerometers are used in mobile systems, cars, turbines and aircraft to provide vibration information and position data. Sensor signals can be amplified or non-amplified to cater to measurement requirements.
There is no universally preferred sensor type for position. In this case, the position you could be measuring may be linear position, rotary position or tilt using a combination of contact or non-contact sensing technologies. It has been measured with sensors for a long time, so both preference and application play a role in making this decision. Factors in selecting a position sensor are environment, excitation, filtering, environment, and whether a line of sight or a physical connection is required to measure distance.
Types include Hall Effect Sensors, Potentiometers, Optical Encoders, Linear Variable Differential Transformers (LVDTs), Eddy-Current Sensors and Reflective Light Proximity Sensors.
There are five common pressure measurement sensor types: absolute, gauge, vacuum, differential, and sealed. Each type is relative to a different reference pressure and could alter your pressure values, so you’ll need to understand which type of measurement your sensor is acquiring. Bridge-based (strain gauges), or piezoresistive sensors, are the most commonly used pressure sensors.
Strain gauge-based load cells are most common for measuring force because they don’t require the same amount of calibration and maintenance as mechanical lever scales. Load cells have many forms, from tension and compression through to torque transducers. They also have many configurations for all purposes, including custom integrated load cells for all forms of force/load sensing.
Whether your application requires a pressure sensor, temperature sensor or load cell, selecting the correct sensor requires you to answer a number of questions.
The nine criteria below provide a framework for how to correctly pair sensors with their specific application:
1. What is being measured? – Are you striving to sense a process parameter, an object’s presence, the position of a mechanism, or the distance to the target?
2. What is the measurement range? What is the measurement limit of the sensor required? Will the target sit within range? How far away from the object should the sensor be?
3. What are the environmental conditions? Is the sensor suitable for the environment it will inhabit? Are there unique conditions, such as high temperatures or winds? Is a specific industrial certification required for your unique application, such as explosion-proof or intrinsic ratings?
4. What type of interface is needed? What type of controller interface or switching logic is required? Does it need to be a digital display, or do you need data acquisition to store/view your measurements?
5. What are the resolution requirements? What is the most granular increment detected by the sensor, and what accuracy specification does the sensor need to satisfy your measurement requirement?
6. What is the target composition? What is the material composition of the substance that will be sensed? Is it metal, plastic or something else entirely?
7. What are the repeatability requirements? Is the variable consistently measured under the same environment? Will the environments change?
8. What is the form factor? How much physical space is available for the sensor, and what form best fits the application? Should the sensor be low-profile, or is there room for tubular housing?
9. How will the electrical connection be made? There are three typical electrical connections for sensors: pre-wired cable with flying leads, integrated quick-disconnect connector, and a pre-wired cable with a moulded-on connector. The choice of each option typically depends on the environment or protection of the sensor.
The use of sensors can enhance our capacity to observe and report on the world around us. There are sensors integrated into just about everything we use these days from smartphones and smartwatches to home and workplace automation products.
With this guide, you’ll now have enough information to know what to look for when selecting the correct sensor. Of course, Applied Measurement is always here to help with this process.
As experienced measurement equipment suppliers since 1976, our sensor solutions at Applied Measurement Australia are unprecedented and have experience in all forms of industry such as Defence, Oil and Gas, Transport, R&D, Maritime, Manufacturing, Process and Control and many more.
Our sensor portfolio includes pressure transducers, liquid level sensors, accelerometers, LVDT/RVDTs, inclinometers, string and linear/rotary potentiometers, load cells, temperature, torque sensors, accelerometers, IMUs and specialty sensors, just to name a few, plus a full range of interface electronics.
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