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Proximity Sensor Operation

Author : KJT Date : 2015-6-8 17:15:10
Proximity Sensor Operation
A proximity sensor is activated by a magnetic field or ferrous material component. There are 
numerous possibilities for sensor orientation within a given magnetic field. The following information 
outlines several key factors to consider when determining proximity sensor operation.
Operate and Release
Operate distance (D) is the dimension between the proximity sensor and the actuator where the 
sensor must operate. Release distance is the dimension between the proximity sensor and the 
actuator where the sensor must release. See Figure 1 for illustrations of proper proximity sensor and 
actuator alignment.
Magnetic Overdrive
Magnetic overdrive is a critical parameter in the operation of proximity sensors providing low and 
stable contact resistance as well as outstanding performance. This is achieved by employing the 
sensor at the recommended must-operate distance or closer.
Milli-Tesla and Gauss
Surface-mounted sensors and small proximity sensors can be conveniently tested for magnetic 
sensitivity using a Helmholtz Coil. This device is a relatively large assembly consisting of two sets of 
windings. The windings are arranged to produce a “zone” or volume of space with uniform magnetic 
field strength. The field strength in the “zone” is directly related to the current in the windings. The 
field strength is measured in milli-Tesla (mT) or Gauss (G).
1mT = 10G
Placing a proximity sensor in the test “zone” of a Helmholtz Coil is an excellent way to test magnetic 
sensitivity. The sensor under test can be subjected to various predetermined fields to verify response 
or non-response to each field. The test system can also determine the exact field strength required 
to operate the sensor. This scheme of testing complies with international standards for implantable 
medical devices, which requires that the devices not respond to certain ambient stray fields.