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IEC 62323: Dimensions of Half Pot-Cores Made of Ferrite for Inductive Proximity Switches
💡 Standard Snapshot: IEC 62323 (First edition, 2005) specifies the important dimensions for mechanical interchangeability of a preferred series of half pot-cores made of ferrite, intended for use in inductive proximity switches. It covers 11 core types from PS 3.3 to PS 68, with complete dimensional specifications and tolerances.
1. Scope and Application
IEC 62323, prepared by IEC Technical Committee 51 (Magnetic components and ferrite materials), defines the critical dimensions for half pot-cores used in inductive proximity switches. These ferrite cores are key components in non-contact sensing applications where the presence of metallic objects is detected through changes in the oscillator circuit’s inductance. The standard replaces the earlier IEC/PAS 62323 published in 2002 and constitutes a technical revision.
Inductive proximity switches operate by generating a high-frequency electromagnetic field from a coil wound on the ferrite core. When a metallic target enters this field, eddy currents are induced, absorbing energy and changing the oscillator’s amplitude. The ferrite core concentrates and directs the magnetic field, significantly enhancing the sensor’s sensitivity and detection range. The standardized dimensions ensure that cores from different manufacturers are mechanically interchangeable, simplifying sensor design and enabling consistent performance.
⚠️ Engineering Insight: The half pot-core geometry is specifically optimized for proximity sensor applications. Unlike full pot-cores that completely enclose the winding, the half pot-core design leaves one side open, allowing the magnetic field to project outward toward the target. The cup shape helps focus the magnetic flux into a concentrated beam, improving detection range and spatial resolution. The ferrite material selected must have high permeability at the operating frequency (typically 50-500 kHz for proximity sensors) while maintaining low core losses.
2. Core Dimensions and Tolerances
2.1 Core Series Overview
The standard defines 11 core types spanning a wide range of sizes suitable for different proximity switch diameters:
| Core Type | Dimensions A x B (mm) | A (mm) | B (mm) | D (mm) | E (mm) | F (mm) |
|---|---|---|---|---|---|---|
| PS 3.3 | 3.3 x 1.3 | 3.35 ± 0.15 | 1.3 ± 0.2 | 0.85 +0.2 | 2.5 +0.1 | 1.20 ± 0.1 |
| PS 5.6 | 5.6 x 1.7 | 5.6 ± 0.25 | 1.7 ± 0.2 | 1.1 +0.2 | 4.5 +0.15 | 2.5 ± 0.1 |
| PS 7.35 | 7.35 x 3.6 | 7.35 ± 0.25 | 3.6 ± 0.2 | 2.8 +0.2 | 5.8 +0.2 | 3.0 ± 0.15 |
| PS 9.0 | 9.0 x 3.5 | 9.0 ± 0.4 | 3.5 ± 0.2 | 2.6 +0.2 | 7.3 +0.3 | 3.9 ± 0.25 |
| PS 14 | 14.3 x 4.25 | 14.3 ± 0.5 | 4.25 ± 0.15 | 2.8 +0.2 | 11.6 +0.4 | 6.0 ± 0.2 |
| PS 25 | 24.8 x 8.9 | 24.8 ± 1.0 | 8.9 ± 0.2 | 5.9 +0.3 | 20.5 +0.8 | 11.3 ± 0.5 |
| PS 35 | 35 x 10.8 | 35 ± 1.0 | 10.8 ± 0.35 | 7.2 +0.4 | 29.4 +0.8 | 15.7 ± 0.5 |
| PS 47 | 47 x 14 | 47 ± 1.3 | 14 ± 0.5 | 9.5 +0.5 | 39 +1.1 | 20 ± 0.6 |
| PS 68 | 68 x 14.5 | 68 ± 2.2 | 14.5 ± 0.6 | 9.0 +0.6 | 57.5 +1.8 | 29.5 ± 1.0 |
2.2 Dimensional Nomenclature
The standard defines five critical dimensions for each core type:
- A (Outer Diameter): The overall outer dimension of the half pot-core, determining the sensor housing diameter required.
- B (Height): The overall height of the core, which affects the coil winding space and the sensor’s profile.
- D (Center Hole Diameter): The diameter of the center hole, if present (optional). This can be used for mounting or for the wire connection feed-through.
- E (Inner Cavity Diameter): The diameter of the internal cavity that accommodates the coil winding. A larger E allows more winding turns or thicker wire.
- F (Outer Groove/Step Diameter): The diameter of the outer groove or step used for positioning the core within the sensor housing.
✅ Design Application: When designing an inductive proximity switch, the core type selection should consider: (a) the sensor housing diameter (dimension A determines the minimum housing size), (b) the required sensing distance (larger cores generally provide greater sensing range), (c) the winding requirements (dimension E and B determine the available winding volume), and (d) the operating frequency (smaller cores typically operate at higher frequencies). For an M12 tubular proximity sensor, the PS 9.0 or PS 11 core would be appropriate, while an M30 sensor would typically use PS 25 or PS 30.5.
3. Quality Requirements and Marking
3.1 Surface Irregularity Limits
The standard mandates that cores be delivered without burrs to avoid damage to the coil and its interconnection wires. Flashes (thin protrusions of material at the mold parting line) are not permitted on the winding area limiting surfaces, including edges and wire connection feed-through holes. This requirement references IEC 60424-1 for guidance on the limits of surface irregularities. The strict surface quality requirements are essential because even small burrs or flashes can:
- Damage the thin enamel insulation of magnet wire during coil winding
- Create stress concentration points that may lead to core cracking during assembly or thermal cycling
- Interfere with the precise positioning of the core within the sensor housing
- Affect the magnetic circuit’s uniformity, potentially causing variations in sensor performance
3.2 Marking Requirements
Manufacturer-specific marking is mandatory for cores of size PS 7.35 and larger, preferably on the bottom of the core. This marking enables traceability and quality assurance throughout the manufacturing and supply chain. The standard notes that the core may have up to two slots for wire connection feed-through holes, and a center hole (H) is allowable if needed for the application.
3.3 Design Flexibility
The standard allows certain design flexibility while maintaining interchangeability:
- Wire Connection Slots: The core may have up to two slots for wire connection feed-through, enabling various winding termination configurations.
- Center Hole: A center hole (dimension H) is allowable but not mandatory, giving designers flexibility in mounting and assembly methods.
- Chamfers: Chamfers are allowable as long as they do not limit the winding space, enabling slight edge modifications without compromising performance.
💡 Proximity Switch Design Considerations: The half pot-core’s open face design creates a directional magnetic field that is essential for proximity sensing. When designing the sensor, the core should be positioned so that the open face faces the detection direction. The coil winding should fill the available cavity space (dimensions E and B) to maximize the magnetic field strength. The choice of ferrite material grade (per IEC 61332 classification) should match the intended operating frequency range, with higher frequency operation requiring materials with lower initial permeability but lower core losses.
4. Frequently Asked Questions
Q: What is the difference between a half pot-core and a full pot-core?
A: A full pot-core completely encloses the winding within two matching halves, providing excellent magnetic shielding but limiting the external magnetic field. A half pot-core uses only one half of the pot-core geometry, leaving one side open. This open face allows the magnetic field to project outward, which is essential for proximity sensing applications. The half pot-core design sacrifices some shielding effectiveness for directional field projection.
Q: How do I select the correct PS core size for my proximity switch design?
A: Consider these factors: (1) the sensor housing diameter must accommodate dimension A; (2) larger cores (PS 25, PS 35, PS 47) provide longer sensing distances but require larger sensor bodies; (3) the winding requirements (number of turns and wire gauge) must fit within the cavity defined by dimensions E and B; (4) the core’s ferrite material must be suitable for the intended operating frequency — typically 50-500 kHz for inductive proximity switches.
Q: Why does the standard specify a center hole as optional rather than mandatory?
A: The center hole is optional because different proximity switch designs may use different mounting methods. Some sensors use a center screw for mounting, requiring the hole, while others use adhesive bonding or press-fitting into the housing, where a center hole is unnecessary. The standard provides flexibility while maintaining outer dimensional interchangeability.
Q: What ferrite material classifications are suitable for half pot-cores in proximity switches?
A: The standard references IEC 61332 for soft ferrite material classification. For inductive proximity switches operating in the typical 50-500 kHz range, materials from classes such as H (power applications, 100-300 kHz), W (wideband, 300 kHz-1 MHz), or M (high permeability, up to 100 kHz) may be appropriate. The specific material choice depends on the operating frequency, required sensitivity, and temperature stability requirements of the application.
