Sensors for industrial control

Sensors come in all shapes, sizes and variants. Sensing for industrial control and manufacturing combines many different technologies. Today sensors must relay precise information back to the control base for clear indication of live the process.

Choosing the correct sensor or combination of sensors is a factor that the design engineers need to consider carefully. The basic understanding of how and what each sensor is capable of measuring is paramount to ensuring that optimal and cost effective solutions are employed to monitor operation and key critical processes within industrial environments.

Two of the most commonly used sensing options in industry are presence sensing and temperature sensing. Below we talk only of sensing options, monitoring and measurement also need careful consideration.

Presence sensing

Inductive Sensor - Detects metallic material, can be used in dirty and wet environments,  has limited sensing distances.

Capacitive Sensor - Detects solids or liquid, can be used in dirty and wet environments, and has limited sensing distances

Photoelectric Sensor - Detects solid objects, suitable for a wide range of targets, has different sensing versions such as; thru-beam, retro reflective and diffuse, good sensing range if the right version is used

Ultrasonic Sensor - Detects solid or liquid, has good sensing distance and can ignore targets in dead band zone.

Fibre Optic sensor – Uses photoelectric principle to detect solids, usually for smaller machinery.

Temperature Sensing

Thermocouples - use the principle of two dissimilar conductors forming a junction which when heated produces a voltage. The temperature scale is dependent on the alloys used to form the junction. Common types of thermocouples include Type J, Type K, Type N and Type T.

PT100 - Platinum resistance thermometers are more precise and usually more expensive than thermocouples. Consisting of a probe which houses a fine platinum coiled, the material changes in resistance as the temperature changes, this resistance change is used to determine the temperature.

Infra red temperature sensors and Thermographic cameras- convert thermal radiation to an electrical signal which can be displayed as units of measure. These sensors are ideal for measuring the temperature of inaccessible or moving objects. Thermographic cameras form an image of the thermal radiation; these are really useful for fault finding and preventative maintenance within industry.

Thermostats-For temperature regulation within equipment, provide feedback or used to open and close circuits outside of temperature parameters.