| Summary: | The non-linear characteristic of a non-contacting Inductive Proximity Sensor (IPS) with the temperature affects the computation accuracy when measuring the target distance in real time. The linear model based method for distance estimation shows a large deviation at a low temperature. Accordingly, this paper presents a non-linear measurement model, which computes the target distance accurately in real time within a wide temperature range from <inline-formula><math display="inline"><semantics><mrow><mo>−</mo><mn>55</mn><mo> </mo><mo>°</mo><mi mathvariant="normal">C</mi></mrow></semantics></math></inline-formula> to <inline-formula><math display="inline"><semantics><mrow><mn>125</mn><mo> </mo><mo>°</mo><mi mathvariant="normal">C</mi></mrow></semantics></math></inline-formula>. By revisiting the temperature effect on the IPS system, this paper considers the non-linear characteristic of the IPS measurement system due to the change of temperature. The proposed model adopts a non-linear polynomial algorithm rather than the simple linear Look-Up Table (LUT) method, which provides more accurate distance estimation compared to the previous work. The introduced model is fabricated in a 0.18 <inline-formula><math display="inline"><semantics><mi mathvariant="sans-serif">μ</mi></semantics></math></inline-formula>m Complementary Metal Oxide Semiconductor (CMOS) process and packaged in a CQFN40. For the most commonly used sensing distance of 4 mm, the computed distance deviation of the Application-Specific Integrated Circuit (ASIC) chips falls within the range of <inline-formula><math display="inline"><semantics><mrow><mo>[</mo><mo>−</mo><mn>0.2</mn><mo>,</mo><mn>0.2</mn><mo>]</mo></mrow></semantics></math></inline-formula> mm. According to the test results of the ASIC chips, this non-linear temperature compensation model successfully achieves real-time and high-accuracy computation within a wide temperature range with low hardware resource consumption.
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