Proximity Sensor

• Capacitive proximity sensors

Capacitive proximity sensors can detect metal and non-metal targets in the form of powders, granules, liquids, and solids. This device is similar to an inductive sensor, except that the inductive sensor's inductive coil is replaced by a capacitive sensing plate. The sensing plate in the sensor forms a capacitor with the target object, and when the object approaches the sensing surface, it enters the electrostatic field of the electrode and changes the capacitance in the oscillator circuit. The oscillator begins to oscillate, and the trigger circuit reads the oscillator amplitude. When it reaches a certain amplitude, it changes the state of the sensor output. As the object moves away from the sensor, the oscillator amplitude decreases, and it switches the state of the sensor output to its original state.

Capacitive is slower than inductive, and can usually detect 1~25 mm, and some sensors can detect 2 inches. Since capacitive sensors are able to detect most types of materials, they must be kept away from non-target materials to avoid false triggering. Therefore, if the target contains ferrous materials, inductive sensors are a more reliable choice.

• Inductive proximity sensors

Unlike other proximity sensing technologies, they can only work on metal objects because they use magnetic fields for detection. Inductive proximity sensors work in two ways.

In the first way, when a target approaches the sensor, the induced current increases, which increases the load on the oscillation circuit, causing its oscillation to be damped or stopped. The sensor detects this change in oscillation state with an amplitude detection circuit and outputs a detection signal.

In the other way, the frequency change caused by the presence of a conductive target is used instead of the amplitude change. Non-ferrous metal targets such as aluminum or copper approaching the sensor cause the oscillation frequency to increase, while ferrous metal targets such as iron or steel cause the oscillation frequency to decrease. The change in oscillation frequency relative to the reference frequency causes the output state of the sensor to change.

As a proximity sensor, inductive proximity sensors are often used in shorter distance applications and can provide extremely fast refresh rates because they are based on the principle of detecting differences in electromagnetic fields. This sensor performs better on ferrous metal materials such as iron and steel.

Under normal circumstances, the signal indicator is a way of reflecting the working status signal of the switch, namely:

In the normally open (NO) state, it is "off"; in the normally closed (NC) state, it is "on".

When the signal indicator is inconsistent with the feedback signal, it indicates that there is an abnormality or bad phenomenon. There are many possible reasons:

1. The sensor and the equipment are wired incorrectly, the working voltage is incorrect, the equipment is short-circuited, etc., which leads to direct badness such as burning, damage, and breakdown of the internal circuit of the sensor.

2. The equipment circuit has poor contact or an unstable short circuit, which causes non-destructive damage to the inside of the sensor.

3. The sensor itself has no protection function. Once the connection is wrong or short circuit occurs, the switch cannot be used directly.

(It is impossible to distinguish whether it is bad or poor operability.)

4. The working voltage is too high, the instantaneous short-circuit current voltage is too high, and the output tube is broken down due to long-term short circuit. The signal light changes, but there is no signal output.

The signal light flashes, there is no signal change, there is a short circuit in the equipment and the connection, and the switch may be directly damaged or saturated if it is not handled for a long time.

It refers to the installation method of the sensor. Flush installation can be buried in metal, while non-flush installation cannot be buried in metal, but the action distance is longer than that of flush installation. Flush installation: The sensor is buried in a metallic base, and its effective sensing working surface is flush with the base surface. Non-flush installation: The sensor is not buried in a metallic base, and its effective sensing working surface must maintain a certain size with its base. For proximity sensors of the same specification, non-flush installation can obtain the maximum sensing distance. The advantages of flush-mounted sensors are: they have better mechanical protection performance and stronger anti-interference ability compared to non-flush-mounted sensors. Compared with non-flush-mounted sensors, the action distance of flush-mounted sensors is about 69% of the latter.

The working principle of capacitive proximity sensors is similar to that of inductive sensors. A capacitor located on the main side of the sensor generates an electromagnetic field. The nearby parts change the intensity and frequency of the oscillation. Unlike inductive sensors, capacitive sensors can detect not only metal parts, but also parts of various shapes and materials (solid, liquid, viscous, powdered, etc.).

The main features of capacitive sensors are:

1.Low range: less than 60 mm

2.Somewhat more expensive than inductive sensors

3.Used for a wide range of parts made of all different materials

4.Can detect objects through non-metallic walls

5.Sensitive to moisture and concentrated vapors

6.Widely used for level detection (i.e. through plastic bottles) and for transparent material detection at short distances

7.No mechanical wear, long stand-alone service life

8.Adapted to industrial environments (polluted atmospheres)

9.High throughput

Inductive proximity sensors are the most popular. They have an oscillating circuit that generates an electromagnetic field. Any metal part that approaches it is detected because it is the source of the induced current, which then reduces the oscillations sensed by the detector.

The main characteristics of inductive sensors are:

1.Can only be used for metal parts

2.Relatively limited range: maximum 80 mm, depending on the nature of the alloy

3.Low cost: half the price of photoelectric sensors

4.Robust, resistant to harsh environments, insensitive to shocks, vibrations, dust, etc.

5.High switching frequency (several kHz), allowing the detection of parts passing at high speeds even when rotating.

6.No moving parts subject to wear

1. Magnetic field interference: Since inductive proximity switches detect whether an object is approaching by detecting changes in the magnetic field, there should be no strong magnetic field around the installation, which will interfere with its normal operation.

2. Unstable power supply voltage: A normal and stable working voltage can ensure the normal operation of the proximity switch. Unstable voltage or short circuit of the power line will cause the proximity switch to fail to work properly.

3. The detected object is not a metal material: The inductive proximity switch can only detect metal materials.

4. Equipment aging: After long-term use, the internal components of the proximity switch will also age or be damaged, which will cause it to fail and need to be checked and repaired.

5. Loose wiring: If the site where the proximity switch is installed vibrates for a long time, this will cause its wiring to loosen, resulting in poor or loose signal transmission, which is reflected in the failure of the proximity switch.

Environmental issues: Generally speaking, the protection level of many imported brands, such as Autonics' proximity switches, is IP66 and above. However, for inductive proximity switches, if there is thick dust on the surface of the detected object, this will inevitably lead to low detection accuracy and have a greater impact on the response speed and sensitivity of the proximity switch.

Inductive proximity sensors will encounter some common faults during use. Understanding the causes of these faults and the corresponding troubleshooting methods can help solve the problems quickly and ensure the normal operation of the production line.

The following are some common faults and their troubleshooting methods:

No output signal

Reason: power supply problem, wiring error, sensor damage or target object is not within the detection range.

Troubleshooting method:

Check whether the power supply voltage meets the requirements and confirm that the power supply is connected correctly.

Check whether the wiring is loose or disconnected.

Confirm whether the target object is within the effective detection range of the sensor.

If the above checks are normal, the sensor itself may be damaged and a new sensor needs to be replaced.

Unstable output signal

Reason: Environmental interference (such as electromagnetic interference), unstable movement of the target object, improper sensor installation or excessive sensitivity.

Troubleshooting method:

Check whether there are strong electromagnetic fields or other interference sources around, and take shielding measures.

Ensure that the object being measured is stable and keeps a proper distance from the sensor.

Check whether the sensor is firmly installed and adjusted to the appropriate angle and position.

Adjust the sensitivity setting of the sensor to adapt it to the current application environment.

False trigger

Reason: sensor sensitivity is too high, environmental factors (such as temperature changes), interference from other metal objects nearby.

Troubleshooting method:

Reduce the sensitivity setting of the sensor.

Check and optimize the working environment to avoid excessive temperature fluctuations.

Clean up metal debris around the sensor to ensure that no unnecessary metal objects affect detection.

Response time is too long

Reason: sensor aging, internal circuit problems or improper load matching.

Troubleshooting method:

Check the working status of the sensor. If the performance is significantly degraded, you may need to replace the new sensor.

Confirm that the load matches the sensor output, and add an isolation circuit or use an intermediate relay if necessary.

If the response delay is caused by a load problem, you can consider optimizing the load configuration.

Shortened detection distance

Reason: sensor is dirty, the material of the target object has changed, or the sensor has aged.

Troubleshooting method:

Clean the sensor surface to remove impurities such as dust and oil.

Check whether the material of the target object has changed, and adjust the sensor parameters to adapt to the new material.

If the sensor has been used for a long time and has aged, it is recommended to replace it with a new sensor.

Frequent damage

Causes: Mechanical shock, overload or harsh environmental conditions.

Troubleshooting:

Re-evaluate the installation location to ensure that the sensor is not subject to direct mechanical shock.

Check the electrical connections to ensure that no overload occurs.

Improve the working environment, such as adding a protective cover or increasing the protection level.

The failure rate of inductive proximity sensors can be greatly reduced through regular maintenance and correct use. If you encounter a problem that is difficult to solve, it is recommended to contact our Garantta Sensor Company technical support department for help. In addition, detailed records of each failure and the process of handling will help to better prevent and deal with similar problems in the future.

Common Problems and Failure Phenomena

1. The proximity sensor cannot confirm the distance range of the detected object.

2. The switch is installed within the detection distance range, and the signal is sometimes detected and sometimes not (sometimes it can be detected, sometimes it cannot be detected).

3. The actual detection distance is different from the standard detection distance indicated by the sensor. (Or less than the detection distance, or greater than the detection distance).

4. The indicator light has a signal prompt, but no signal output; or the signal indicator light is always on without signal change; or the signal keeps flashing, etc.

5. There is no action response after the power is turned on, or there is no signal feedback.

6. Can multiple sensors be connected at the same time, etc. (The device can distinguish the feedback signals of different sensors, so multiple sensors can be connected at the same time).

How to solve various problems in actual applications?

You should understand what type of switch you purchased belongs to, its unique product characteristics and basic application principles, installation methods, precautions, etc. The information about the inductor proximity switch sensor produced by our company is as follows.

1. Inspection method of inductive proximity switch

Inductive proximity switch is a contactless switch (i.e. switch type sensor), which is generally used in mechanical automatic control equipment with high positioning accuracy, long service life, fast response speed and convenient installation. It is mainly used for limit, reset, stroke positioning, counting, automatic protection, and micro switch replacement. The object to be detected by the inductive proximity switch sensor must be a metal object. For non-metallic objects, the inductive proximity switch will not work. It has the characteristics of waterproof, shockproof, oil-proof, dustproof, corrosion-resistant, etc., and has strong applicability to harsh environments.

2. Output signal of inductive proximity sensor switch

Proximity switch is a general term for contactless sensors, and its types include: inductive, capacitive, and Hall. The output signal of the inductive proximity switch described this time is mainly: the switch quantity signal of open or closed (that is, if there is a metal object at any position within the maximum range detected by the proximity switch sensor head to the product, a switch signal will be given. When the object is not within the detection distance range, the sensor switch signal is opposite to the action).