Technical Notes

Technical Notes

Magnetic Reed Switch Technology and Protection

Magnetic reed switch technology has been a proven technology for more than 50 years to dependably and safely sense a wide range of liquids and positioning. The internal switches are hermetically sealed and capable of switching 1/8" accuracy and 1/32" repeatability for standard vertical switches. Magnetic reed switches, when used to electrical specification, can switch reliably for millions of cycles unaffected by everyday shock and vibration for years of dependable operation.

Magnetic reed switch operation is simple but reliable. The float moves a sealed permanent magnet along the stem as the fluid rises and falls. As the magnets pass over the switch, the reeds are pulled together to create a highly reliable contact. The sealed stem encapsulates the hermetically sealed reed switch and its wires from the liquid environment.

Float Switch Cross Section
Cross Section View 

Most SMD Float Switches can be configured for either Normally Open (NO) or Normally Closed (NC) switching by changing the float orientation. NO and NC refer to the switches position at rest in a "DRY" tank!  Single Pole Double Through (SPDT) contacts are also available. Each SMD Float switch is tested 100% before shipment for guaranteed performance!

Reed Switch Protection

One of the greatest failures of reed switches is caused by over current conditions. Most electrically listed products are rated for the "Steady State" operating power. This is the time when normal operation occurs and does not take into account the "turn-on" or "shut-down" loads associated with capacitive or inductive devices. The power created by these devices at "turn-on" or "shut-down" can be 5 to 10 times the "Steady State" current given as part of the power rating. The power spikes created at these moments can cause arcing which can weld or completely burn open the reed contacts. SMD reed switches list the UL resistive power ratings for the reed switches, and maximum currents and voltages to be switched. In most high power applications an inexpensive relay can be used to isolate you switch from heavier loads.  Improper wiring is often the cause of switch failure.  When wiring you switch and relay combination (as shown in figure 6) remember to tie the load and the switch as close as possible to the ground source to reduce any load spikes from traveling through the switch. 

Listed below are a few protection methods to insure many years of dependable service.

Figure 1
DC Load Protection

Figure 4
AC Load Protection

Cable Float Switches

Proximity Switches

  • Magnetic Proximity Switches
  • Inductive Proximity Switches
  • Capacitive Proximity Switches
  • Photoelectric Proximity Switches

Accessories for Alarm Systems

  • Magnetic Proximity Switches
  • Inductive Proximity Switches
  • Capacitive Proximity Switches
  • Photoelectric Proximity Switches

PIR Sensors

  • Pet-immune Passive Infrared Detector IR-580P
  • Pet-immune Infrared Detector RX-40PI, Optex Make
  • PIR Immune Dual Technology Detector, DP-550P
  • 360° Ceiling Mount PIR Detector, SR - 613W
  • Outdoor PIR Motion Sensor, OPTEX LX-402
  • Passive Infrared Detector

Energy Saving Sensors

  • EnergySaving Smart Switch, HC-7C
  • PIR MOTION Sensor For Light Control With Manual Override, HC-7D
  • PIR Motion Sensor For Lights, HC-7E
  • Ceiling Mount PIR Motion Sensor With Light,HC-25A
  • Halogen Lamps PIR Sensors HC-150W / 500W
  • 200° Passive Infrared SenSwitch LC-200 / 200HD / 200LV

Contact Us

Hamilton Electronics Pvt. Ltd.

B- 36/5, G.T. Karnal Road
Industrial Area
New Delhi - 110 033, India

Ph. No. 91-11-27245389,
27249931, 27451984
Fax No. 91-11-27461984
Email :