Deviating from thumb rules
Some applications do not allow enough room for an appropriately sized target. If the ideal target diameter is not possible, measurement can still be achieved with reduced performance. Contact the manufacturer’s applications engineering group to determine how the performance will be affected.
Sensor mounting considerations
The electromagnetic field produced by eddy current sensors extends in front of the sensor face, radially from the sensor OD, and, to a small degree, behind the sensor face. Any electrically conductive material in the sensor field can affect the system output. Because of this, care must be taken when installing sensors to ensure that maximum sensitivity of the system is achieved.
Shielded and unshielded sensors
The stainless steel housing of shielded sensors typically extends to the face of the sensor. This results in the electromagnetic field from a shielded sensor being somewhat smaller than that of an unshielded sensor.
In unshielded sensors, the sensor face containing the coil protrudes in front of the stainless steel housing. This allows for a larger electromagnetic field and the larger calibrated ranges typical of unshielded sensors.
Deviating from typical mounting
In some applications, it is impossible to maintain the clearances specified in the drawings. This does not mean that a precise measurement is impossible to make. Conductive material other than the target that engages the field is called side loading. In-situ calibration or bench calibration with simulated side loading can, in most cases, eliminate the concern.
Dan Spohn is regional sales manager for Kaman Precision Products/Measuring, a division of Kaman Aerospace Corp.