RFCapacitive Sensor vs. Inductive Sensor: Key Differences
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This article compares capacitive and inductive sensors, highlighting their differences across various parameters.
Introduction:
Both capacitive and inductive sensors offer non-contact sensing solutions. These sensors rely on changes in physical properties to detect objects. Capacitive sensors measure changes in capacitance, while inductive sensors measure changes in electromagnetic fields. These sensors are widely used in industries such as industrial automation, robotics, consumer electronics, manufacturing, and automotive.
It’s important to note that both sensor types require an external power supply to operate.
Capacitive Sensors
A capacitive sensor detects changes in capacitance to determine the presence or proximity of objects. These sensors offer non-contact sensing and are generally unaffected by the material of the detected object. They’re commonly found in consumer electronics for applications like proximity sensing, liquid level sensing, touch sensing, and moisture detection.
However, it’s worth noting that capacitive sensors can be sensitive to environmental factors like temperature and humidity.
Capacitive level sensing operational diagram.
The figure above illustrates the operational diagram of capacitive level sensing. It consists of two conductive plates (electrodes) separated by a dielectric material. When the liquid level changes, the capacitance between the plates changes due to the change in the dielectric. This change in capacitance is detected by the sensor’s electronics, which then triggers an output signal or response.
Inductive Sensors
An inductive sensor detects electromagnetic (EM) induction to determine the presence or proximity of metallic objects. They also offer non-contact sensing and are well-suited for applications where physical contact is undesirable. Common uses include proximity detection, metal sorting, speed sensing, and level sensing.
Keep in mind that inductive sensors are sensitive to the distance and size of the object being detected, as well as the conductivity of the material.
Inductive sensor (proximity sensor) operational diagram.
The figure above shows the operational diagram of a proximity sensor based on inductive sensing. It consists of a coil of wire, an oscillator circuit, and a current sensor. When alternating current (AC) passes through the coil, it generates an electromagnetic field. When a metallic object enters the sensor’s sensing range, it interacts with the electromagnetic field, causing a change in the coil’s inductance. This change is detected by the oscillator circuit, which then triggers an output signal or response.
Capacitive Sensor vs. Inductive Sensor: Key Differences
The following table compares capacitive and inductive sensors based on various specifications:
| Specifications | Capacitive sensor | Inductive sensor |
|---|---|---|
| Typical sensing range | 0.01 mm to 10 mm | 0.1 mm to 15 mm |
| Sensing area (required) | 130 % of probe diameter | 300 % probe diameter |
| Resolution | 2 nm | 2 nm |
| Probe size (typical) | 800 % of range | 300 % of range |
| Rotating targets | Unaffected | Small errors on ferrous targets |
| Gap material | Senses changes in non-conductive gap material | Ignores non-conductive gap materials |
| Target material | Not affected by material differences | Affected by conductive material differences |
| Non-conductor measurement | Measures non-conductors (plastics) | Does not measure non-conductors |
| Cost | More | Less |
| Major applications | - Touch sensing in consumer electronics - Liquid level sensing - Moisture detection | - Speed sensing in machinery - Metal sorting - Level detection in tanks (detecting metal floats) |
