Sensor suitability: Selection matters

As the range and capabilities of industrial sensors expands to meet the growing needs of industry, selecting the most appropriate sensor for the individual project becomes increasingly important.Phil Dyas, sensor specialist, SICK (UK), comments

Modern manufacturing facilities, warehousing and process environments rely on sensors and sensing systems for everything from quality control and presence detection to ensuring operator safety. Selecting the right sensor can have a significant impact on a business, enabling immediate benefits in terms of quality improvement, energy savings and manufacturing speed and volume.

It's surprising how many manufacturers voice concerns about sensors in-situ on for example, production or packaging lines, only to find the machine design has actually been modified to suit the sensor limitations. The range of sensing systems on the market is vast. This, combined with the sensor manufacturers' ability to modify a sensor to meet the exact application needs, means the sensor can and should be specified to meet individual project requirements rather than the other way around.

Off the shelf solutions may, of course, suit exactly, and being able to call on the resources of a comprehensive product range is advantageous. But very often simple modifications can achieve a best practice solution at little or even no cost.

Sensors can control critical points of production, and an unsuitable solution can allow faulty products through, cause line outages, and affect timing and phasing, resulting in poor margins. In these creditsqueezed times, product and energy waste is unforgivable. Knowing the environment in which the sensor will operate and how this could affect its operation is key to ensuring optimal performance.

External influences The environmental conditions of each production facility, which might include exposure to high frequency lighting or EMC, for example, can have an impact on the type of sensor specified. It's important to examine how such factors might affect the performance of certain sensor types. For example, sensors deployed on a logistics site, where mobile phones or two way radios are in use, must be able to eliminate errors and false operation caused by radio frequency emissions. High frequency lighting and even flashing beacons on forklift trucks can also cause spurious triggering of optical sensors.

Low temperatures Sensors used in cold store environments can be exposed to temperatures as low as -40°C.

If located near a door, where the temperature is likely to rise periodically, condensation may occur on the lens, which could also freeze and ice over when the temperature drops again. To counteract this, sensors with heated lenses and heated reflectors should be considered. The type of cabling must also be considered; PVC cabling is commonly used on sensors, however, it turns brittle at low temperatures.

High temperatures Specifying sensors for high temperature environments, such as the steel and glass industry, also poses unique issues.Most sensors have an operating temperature limit of 70°C, which is far exceeded in such environments. Specifying a sensor with cooling plates and high temperature reflectors can extend the operating envelope to around 100°C. Specifying a metal housing and glass lenses as opposed to plastic will also combat any issues with melting.

Vibration In environments where conveyor belts are in operation, excessive vibration can cause sensor misalignment and where forklifts are used the likelihood of knocking a sensor is increased. Specification for such environments should include a high-strength wrap around bracket providing protection against physical damage and protecting the electrical supply connection.

Given the variety and complexity of sensors available, it is not uncommon for engineers and manufacturers to simply specify sensors within their comfort zone rather than those that are right for the job. Selecting a sensor which is not fit-for-purpose will have an impact on productivity, maintenance, quality, and inventory, as well as cost. An indepth understanding of the range of sensors available, and the impact of operational conditions, is essential when specifying sensors.