Eddy-Current Sensors FAQ

1. Does my target have to be a minimum thickness?

2. Which sensor type is better, capacitive or eddy-current?

3. What materials work best with eddy-current sensors?

4. Can I use my eddy-current sensor with aluminum AND steel?

5. Can I recalibrate my sensor in the field?

6. How is linearity calculated?

7. Can I change the cable length?

 

1. Does my target have to be a minimum thickness?

Yes. The magnetic field from an eddy-current sensor penetrates into the target material. The targets must be thick enough to allow sufficient penetration. Minimum thickness is dependent on material and other factors. It can range from 0.01mm to 2mm. For more information, please see the Minimum Thickness TechNote.

2. Which sensor type is better, capacitive or eddy-current?

Each sensor type has advantages and disadvantages. Please see our Capacitive and Eddy-Current Comparison page to help determine the best solution for your application, or contact us and we'll be happy to help.

3. What materials work best with eddy-current sensors?

Systems are calibrated for maximum performance to specific materials when ordered. Performance is slightly higher with nonferrous materials, but the difference is often negligible.

4. Can I use my eddy-current sensor with aluminum AND steel?

No. Nonferrous materials (aluminum, brass, zinc) produce different reactions from eddy-current sensors than ferrous materials (iron, magnetic steel). A sensor calibrated for one nonferrous material (aluminum) can be used with a different nonferrous material (brass) with only small losses in performance. Sensors calibrated to a ferrous material may change significantly if used with a different ferrous material.

5. Can I recalibrate my sensor in the field?

Yes, if the material type is the same. Sensors have internal factory calibration which is material dependent. A sensor ordered for nonferrous material cannot be recalibrated for ferrous material without being returned to the factory. Nor can a ferrous calibration be recalibrated to nonferrous materials without being returned to the factory.

To recalibrate to the same type of material, see our Eddy-Current Sensor Calibration Technote.

6. How is linearity calculated?

The linearity specification is the measurement of how far the output varies from a straight line.


Linearity Error -
Measurement data is not on a straight line.

To calculate the linearity error, calibration data is compared to the straight line that would best fit the points. This straight reference line is calculated from the calibration data using a technique called least squares fitting.

The amount of error at the point on the calibration curve that is furthest away from this ideal line is the linearity error. Linearity error is usually expressed in terms of percent of full scale. If the error at the worst point was 0.001mm and the full scale range of the calibration was 1mm, the linearity error would be 0.1%.
Note that linearity error does not account for errors in sensitivity. It is only a measure of the straightness of the line and not the slope of the line. A system with gross sensitivity errors can be very linear.

7. Can I change the cable length?

Changing cable length after you receive the sensor will alter the calibration or render the sensor nonfunctional. You can order your sensors with custom cable lengths to match your installation needs.

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