What Is a Sensor? Industrial Sensor Types and Selection
An industrial sensor detects the presence or position of an object and signals a control device; inductive, capacitive and photoelectric types are available.
What is an industrial sensor and where is it used
An industrial sensor is a device that detects the presence, position or level of an object on a machine or process line and converts it into an electrical output signal that a control device such as a PLC, relay or counter can read. Counting products on a conveyor, monitoring press or cylinder position and seeing the fill level in a tank are typical applications.
Proximity sensors detect without touching the target; on the other hand, each sensor type detects only certain target materials. The correct selection is therefore made by first looking at the material to be detected.
Types of industrial sensors
| Sensor Family | Detected Material | Typical Sensing Range | Catalog Link |
|---|---|---|---|
| Inductive Sensor | Metals only (steel, stainless steel, aluminum, brass, copper) | 1 mm – 40 mm (depends on barrel size and flush/non-flush mounting) | Inductive Sensors |
| Capacitive Sensor | Metals + non-metallic solids and liquids (plastic, glass, wood, grain, water) | 2 mm – 25 mm (adjustable sensitivity) | Capacitive Sensors |
| Photoelectric Sensor | Opaque or translucent objects (boxes, bottles, labels, pallets) | 10 mm – 30 m+ (diffuse, retro-reflective, through-beam) | Photoelectric Sensors |
| Temperature Probe (PT100 / TC) | Process, mold, liquid or flue gas temperature | -200 °C to +1200 °C | Temperature Probes · PT100 vs Thermocouple |
The main groups in the store are divided by sensing principle.
- Inductive sensor: Detects only metal targets; with non-ferrous metals such as aluminum, copper and brass, the sensing distance is generally shorter. Models with cylindrical housings (M8, M12, M18, M30), square and rectangular housings, and the AC 2-wire, DC 2-wire and DC 3/4-wire varieties are grouped under Inductive Sensors.
- Capacitive sensor: Can detect metal and non-metal targets; in the form of powder, granules, liquid and solid. It is considered for plastic targets and for granule or liquid fill applications. The products are in the Capacitive Sensors category.
- Photoelectric sensor (photocell): Works by interruption of a light beam or by reflection from the target; materials other than metal can also be detected. The products are divided into cylindrical and rectangular housing groups under Photoelectric Sensors.
In addition to these, Fiber Optic Sensors, Light Barriers, Magnetic and Piston Sensors and Special-Purpose Sensors are in separate categories.
Sensing methods in photocells
Three methods are common in photoelectric sensors, and each requires a different layout.
- Through-beam: The emitter and receiver are in separate housings and are placed facing each other; the object is detected when it interrupts the beam. Examples of through-beam photocells are in the category.
- Retro-reflective: The emitter and receiver are in the same housing, a reflector is placed on the opposite side and the object is detected when it interrupts this light path. Reflectors are found separately in the Photoelectric Sensor Reflectors category.
- Diffuse: The emitter and receiver are in the same housing and there is no reflector; the target itself reflects the light back. For this reason the sensing distance is strongly affected by the reflectivity of the target.
What to look at when choosing an industrial sensor
- Target material: If it is metal, an inductive sensor; for non-metallic materials such as plastic, a capacitive or photoelectric sensor is considered; for liquid or granule fill applications, a capacitive sensor is taken up.
- Sensing distance and method: It is given in mm or cm in the product names; the clearance at the mounting location and the position of the target determine the distance. For a photocell, the reflectivity of the target is also taken into account.
- Housing and mounting: The diameter such as M8, M12, M18 and M30, a square housing, or a plastic or stainless metal housing is chosen according to the place on the machine. There are flush and non-flush head types; mounting limits close to the surrounding material are determined according to manufacturer data.
- Supply and number of wires: There are AC 2-wire, DC 2-wire and DC 3- or 4-wire varieties; connection and supply are made according to the project and manufacturer data.
- Output type: NPN or PNP with NO, NC or NO+NC output must match the structure expected by the PLC input module or relay it will be connected to.
- Connection type: In contrast to cable output, models with connectors such as M12 need a suitable plug and cable; for these, see the Sensor Connectors and Cables category.
For the input side that will read the sensor output, the PLC Input and Output Modules category can also be reviewed.
Brands in this category
- Lanbao: Diffuse and through-beam photocells and DC 3-wire inductive sensors in diameters such as M8 are listed.
- Isıso: M8 and M18 inductive sensors, diffuse and retro-reflective photocells and connector models are available.
- ABB: Contactless safety sensors named Adam, Eva and M12-C61HE are listed.
Order notes
Products are sold per piece. Some products are listed as made to order; for these, the lead time is verified separately. If the exact model is known, you can search by stock code or model code.
Frequently asked questions
What is a capacitive sensor?
A capacitive sensor is a contactless sensor that detects the change in the electrical capacitance of the sensing surface as a target approaches. Because it can detect metal and non-metal targets, in the form of powder, granules, liquid and solid, it is considered for plastic targets and for granule or liquid level applications. Sensing distance and sensitivity are determined according to manufacturer data.
What is the difference between a capacitive sensor and an inductive sensor?
An inductive sensor detects only metal targets. A capacitive sensor can also detect non-metallic materials, for example plastic, liquid and granules. For this reason, if the target is metal, an inductive sensor is considered, and if it is a non-metallic material, a capacitive sensor; sensing distance, mounting location and sensitivity setting are determined according to manufacturer data.
Which sensor detects a plastic object?
An inductive sensor detects only metal targets and does not detect plastic. For plastic targets, a capacitive sensor or a photoelectric sensor is considered. Because the range of the diffuse method in a photocell is affected by the reflectivity of the target, the choice of method and sensitivity should be made according to manufacturer data and application conditions.
What is the difference between NPN and PNP output?
When a sensor with a PNP (sourcing) output detects an object, it supplies the positive supply voltage to the output line. In a sensor with an NPN (sinking) output, the output line is pulled to the 0 V side on detection. To ensure the sensor output is compatible with the PLC input module it will be connected to, the manufacturer data of both should be compared.
What do NO, NC and NO+NC mean on a sensor output?
An NO (normally open) output stays inactive when the target is not detected and becomes active on detection. An NC (normally closed) output is the opposite. NO+NC models have outputs providing both states together. Which one is required is determined from the project data according to the PLC program and control logic.