Non-Contact (Reed) Proximity Switches

Non-Contact Hermetically Sealed (Proximity) Switches are magnetically operated SPST or SPDT “reed” switches with contacts hermetically sealed in a glass capsule. Positioning a magnet next to the switch causes the contact “reeds” inside the switch to flex and touch, completing the circuit. Sealed within the capsule are protective inert gases or a vacuum that prevents the contacts from corroding, keeps the contacts clean and protects the contacts for the life of the device.

Operation of the Switch

In order to trip proximity type switches, magnets are utilized with their magnetic fields to operate the switches. These magnets are placed and sealed in plastic cams that are located on the rotating shaft inside of the limit switch. When the shaft rotates and the cams with the embedded magnets rotate to a position that is proximal to the reed switch, the magnet will trip the switch.

Key Features of the Switch System

A well-designed limit switch secures the vertical alignment of the shaft and cam assembly so that during operation vertical shaft motion is prevented, even under severe conditions. Moniteur utilizes a Loc-Ring that permanently fixes the shaft vertical position in the limit switches and thus prevents any large vertical movements that are found in other designs. One design to avoid is using c-clips to secure the shaft position on the exterior of the unit. Over time and under certain loads the c-clip corrodes or can snap off during rough treatment and loads. The Loc-Ring design prevents the  cam magnet assemblies from moving vertically and possibly tripping other switches.

Common Applications

• Corrosive or humid environments – Non-contact switches eliminate the potential corrosion of exposed contacts found in the design of mechanical switches
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  SPDT or SPST circuit configurations – From an application standpoint, Non-Contact switch configurations are similar and interchangeable with mechanical switches. With a similar configuration, no rewiring or reprogramming is required to upgrade to these non-contact switches.
• Nonincendive (Class 1, Division 2) Applications – Article 501-3 (b) of the NEC (National Electric Code) permits the use of general-purpose enclosures in Class 1, Division 2 locations when the current interrupting contacts are sealed within a hermetically sealed chamber.
• Intrinsically Safe Applications – Non-Contact Proximity switches are passive devices and can be used in intrinsically safe systems with an appropriate voltage and current limiting barrier.
  

Contact Materials

• Tungsten – The choice for high power AC and DC switching applications. Tungsten contacts can handle up to 3A at 120VAC and 2A – 24VDC. These contacts are also available for 220V applications. Tungsten is not recommended for low power DC signals.
• Rhodium – The choice for reliable low power 24 VDC switching applications. Rhodium contacts have 80% less contact resistance than Tungsten, making it the ideal material for DC. These contacts are rated to 1A – 24VDC and are stable down to 1mA at 1V.