Inductive proximity switch parameters

Inductive proximity switch common parameter introduction: (Recently updated content as of 2023-07-29)

1: Standard detection object

As a detection object to measure basic performance, its material, shape, and size are specified.

International standard: Iron material, the shape is a square similar in size to the detection surface diameter of the proximity switch or a circle with a diameter three times the sensing distance.

The detection object of Dipole Technology is a standard detection body, made of iron, with a square shape, smooth surface, and size related to the product outer diameter. For example, M12 uses a square with a side length of 12mm and a thickness of 1mm. M18 uses a square with a side length of 18mm and a thickness of 1mm, and so on.

2: Distance-related parameters

2.1 Detection distance Sn (also known as set distance)

Move the standard detection object using the specified method, and measure the distance from the sensor-detected reference position (reference plane) to the sensor action.

The proximity switch distance is related to the diameter and also to the installation method. The installation method here mainly refers to "flush-type" and "non-flush-type" for products. Generally, the sensing distance of the non-flush type is nearly twice that of the flush type. For example, the flush type of M18 is 5mm, and the non-flush type is 8mm. For general-purpose proximity switches, there are several diameters. Due to different technologies used by various manufacturers, especially some special products made by foreign manufacturers with ultra-long distances, it is difficult to describe. The following examples are all for normal situations:

M3 sensing distance is 0.5~1mm (split type)

M4 sensing distance is 0.5~0.8mm

M5 sensing distance is 0.5~1mm

M6.5 sensing distance is 0.8~1.5mm

M8 sensing distance is 0.8~1.5mm

M12 sensing distance is 2~4mm

M18 sensing distance is 5~8mm

M30 sensing distance is 10~15mm

M40 sensing distance is 15~20mm

M50 sensing distance is 20~25mm

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2.2: Reliable distance

Including the influence of temperature and voltage, the stable interval between the sensor detection surface and the (standard) detected object through position is measured. The recommended value is typically 70% to 80% of the set detection distance. For example, if the manufacturer's set distance is 20mm, then a distance below 16mm is a very reliable distance.

2.3: Reset distance

When the detected object is in the detection area and triggers the sensor, as the detected object slowly moves away from the detection area, there is a critical point at which the sensor has no action. At this point, the distance between the detected object plane and the sensor detection surface is the reset distance.

2.4: Deviation distance (also known as hysteresis distance, referring to the differential distance, with its value known as the hysteresis value or differential value)

Detailed description: When the detected object slowly approaches the detection area until the proximity switch is triggered (i.e., the action distance indicator lights up or goes off), and then slowly moves the object out of the detection area until the switch resets (the indicator light goes off or lights up). The distance between these points is called the hysteresis distance.

Brief introduction: Reset distance - Detection distance = Hysteresis distance

The differential distance should be less than 10% of the detection distance. It is worth noting that too large a hysteresis distance can lead to poor sensitivity, while too short can lead to interference. In general, the hysteresis distance chosen by the manufacturer is around 1% to 3% to balance the overall performance of the switch.

3: Calibration coefficient

Also known as attenuation coefficient, different metal materials have different magnetic permeabilities, so the sensing distance varies. Therefore, different metal materials will experience attenuation based on the set distance. The values for common metals are as follows.

Material attenuation coefficient (reference)

4: Operating mode

4.1: Shielding type (also known as flush type, embedded type)

The shielding proximity switch mainly refers to embedding the internal detection object of the switch in a metal shell, concentrating the magnetic field signal in one area. Therefore, the shielding-type proximity switch does not produce side interference and can be embedded in metal, flush with the outer surface.

During installation, the sensing surface can be flush with the metal surface. The distance from the switch surface to the opposite metal object must be > D Sn, indicating the set distance. The distance between two adjacent switches must be > D (switch diameter).

4.2: Non-shielded (also known as non-flush, non-embedded type)

The non-shielded proximity switch mainly refers to exposing the detection magnetic core inside the switch outside the metal shell, causing the magnetic field to spread to a certain extent. This can achieve an extended distance. However, it also brings problems such as side induction, thus there are installation restrictions.

The distance of the non-shielded sensing head usually refers to the distance between the sensing surface and the closest shell, which is the distance the sensing head is exposed. There must be no magnetic materials around this distance. If there are magnetic materials around, the surface of the magnetic material must be kept at a distance 3 times the Sn from the proximity switch.

5: Response frequency

The maximum number of switchings detected per second.

The higher the response frequency, the better. Different diameters have different frequency response speeds. The smaller the outer diameter, the higher the frequency. For example, the response frequency of a good M18 switch is 600Hz/second, and it can actually reach over 1K, or even as high as 1.5K. Ordinary domestic switches are generally around 300Hz, while foreign ones are generally between 400Hz and 700Hz. The output waveform must be a standard square wave, and the period must be fixed within a very small range of variation, generally only a few tens of microseconds. Otherwise, it is considered a distorted waveform, which is not allowed in industrial control.

6: Temperature Range

This refers to the temperature range of general-purpose inductive proximity switches, which must be within -20 to +70°C for stable operation. Due to temperature drift in electronic components, high-quality proximity switches come from strict requirements for components, such as the precision and temperature coefficient of resistors, strict requirements for manufacturing processes, strict requirements for circuit principles, and other comprehensive factors. The temperature drift range must be controlled within: Change distance / set distance<10%<>

Temperature Deviation Standard:

Product temperature deviations are generally within the above range. For example, let's take the M18 inductive proximity switch. After being placed in a constant temperature box at -20°C for 3 hours, the distance shortens by 0.2mm. After being placed at 80°C for 3 hours, the temperature increases by 0.1mm.

7: Power Supply Voltage

Each product has detailed specifications. For fixed-pole products, the DC series is generally 10V~30V, and the industrial control voltage is usually 12V or 24V. The AC series products are generally 90V~220V, and industrial control is typically 220V. The dual-use of AC/DC is generally 20V~270V, covering a wide voltage range. The commonly used voltages in the industry are mostly 24V and 220V.

8: Rated Voltage

In general, as long as it is within the voltage range, it can operate stably. The so-called rated voltage here is usually the commonly used voltage in industrial control.

9: Voltage Drop

Voltage drop refers to the voltage at the two ends of the proximity switch after it works with the load. For example, in the case of a PNP-NO three-wire proximity switch, the brown wire is connected to 24V, the blue wire is connected to 0V, and the black wire is connected to the load. One end of the load is connected to the black wire, and the other end is connected to the blue wire. When the switch is operating, the voltage at the two ends of the brown and black wires is the voltage drop of the switch. The smaller the voltage drop, the better, as a smaller voltage drop means a larger voltage obtained by the load. If the voltage drop is too large, the power supply to the load may be insufficient, leading to unstable operation. Therefore, in some cases, the voltage drop is used as an important parameter. Generally, the voltage drop of the two-wire DC and two-wire AC is much higher relative to the three-wire DC, especially after adding some protection circuits, the voltage drop is increased. Fixed-pole products have advantages in voltage drop. For example, the voltage drop of the two-wire DC is less than 2.7V without protection. After adding all protection and functions, the voltage drop can still be controlled below 5V. The AC can be controlled below 6.5V at 270V, which is a relatively good level. Other manufacturers generally have a voltage drop of 8V~10V or even higher.

10: Maximum Output Current (max)

Each product has detailed specifications, generally outputting 200mA, which basically meets the requirements of various control fields. For AC/DC, it is usually 500mA, and the current can be customized and sometimes selected according to special customer needs. For fixed-pole products, when the output load is too small and the current exceeds the maximum current, the output current will be maintained at around 10mA, serving as overload protection.

11: Minimum Operating Current (Imin)

The minimum operating current that can meet stable operation of the product. In most cases, the minimum current for stable operation is 1mA, but it may actually be smaller. However, in order to work stably, it generally must be greater than this value.

12: Leakage Current (Ir)

It is the residual current in the load when the proximity switch is not turned on. The smaller this current, the better, as lower power consumption indicates better driving capacity for the load. Simply put, for example, for a 220V AC switch with a relatively large load resistance, the required current to be provided must meet 1mA. If the leakage current is too large, say 3mA, it means the minimum operating current is only 5mA, and the load cannot be driven. Therefore, the smaller the leakage current, the better. The leakage current of fixed-pole products is generally around 0.5mA.

13: IPxx Dust and Water Protection Level