Ampere Turn Selection

For any application, it is important to select the correct Ampere Turn (AT) or magnetic sensitivity of a Reed Switch, Reed Sensor or Magnet Sensor. This is because for a given actuating distance requirement, there will be multiple combinations of magnetic sensitivity and strength of magnet that may match the required ON/OFF distance band. Selecting the right combination ensures long life in the field and also does away with problems such as intermittent operations.

A higher AT band would be require if there needs to be more resistance to shock and vibration, or when there are stray magnetic fields in the vicinity, or there is a need to switch higher currents or loads. In some cases altering the design of a magnet may not be possible as it has already been designed in, and in such cases where strong magnets are used, higher AT bands will be suitable. A flip side to using higher AT bands is that the operate time will be slightly longer and in critical time driven applications, this may not be acceptable.

A lower AT band would be required, where sensing requirement may be required for very low magnetic fields, or when there is a cost implication and in such cases smaller magnet can be used. As most applications use rare earth magnet these days, the cost is based on the actual volume of rare earth metals used in the magnet. Another advantage is that for very low sensing times, where milliseconds of switching time matter, lower AT bands work. A flip side in using Reed products in lower AT bands is that external shock or vibration could cause intermittent unwanted closures, and the contact resistance could be higher than 150 milliohms.

This is why correct Ampere Turn selection matters.