Understanding Smart Sensors - Nomads.usp

Mechatronics and Sensing Systems 269control with ground loops and other EMI paths [19]. Sensors easily can beaffected, depending on the wiring. Isolating the wiring, avoiding ground loops,and in some cases using shielded wiring may be necessary to avoid problems.In automotive applications, some manufacturers require the sensor towithstand electric fields of magnitude up to 200 V/m in the engine compartmentand up to 50 V/m in the passenger compartment [20]. Performance levelsand measurement methods are defined in a number of SAE documents, includingSAE J551, SAE J1816, SAE J1113, SAE J1407, and SAE J1338. Classificationsof failure-mode severity are provided in SAE J1812.An example of automotive testing for EMI is demonstrated by the qualificationtesting for a plastic-packaged integrated pressure sensor. The testingrequired performance at 200 V/m radiated immunity from 10 kHz to 1 GHz.That is one of the higher signal strength levels specified in automotive standards.However, required performance depends on the customer specification.Over 30 EMI specifications have been reported for engine control applicationsaround the world; there is no common standard [21]. The following field characteristicswere defined:• Field strength = 200 V/m;• Frequency range = 1 kHz to 1 GHz;• Modulation = AM, 30% with 1-kHz sine wave;• Polarity = vertical and horizontal;• Criteria for acceptable performance of device under test (DUT): alternatingcurrent (AC) ripple = ≤ ±50 mV.Testing results included (1) passing the test and (2) finding that the testsetup played a significant role in defining the device response and real susceptibility.Furthermore, due to the number of specifications that exist and to verifyacceptable performance of product in the plastic package for two specific applications,additional tests were conducted. An extreme amount of EMI isencountered in a direct RF injection test. Direct RF injection is performed bysoldering the harness to an impedance network. A 100-V/m signal was injecteddirectly into the leads of the plastic packaged sensor. To pass the test, a filtertechnique was developed that greatly improved the performance of a plasticpackagedintegrated pressure sensor even under the toughest testing, includingthe direct RF injection test.