NXP TPMS Sensitivity Difference between FXTH87 and FXTH87E Sensors
FXTH87E sensor modifications impact sensitivity levels compared to the FXTH87 sensor, affecting pressure and acceleration readings. Tolerances and usable ranges vary between the two sensors, requiring adjustments in customer application software for accurate threshold settings. Explore the detailed comparison and adjustments needed for FXTH87E integration.
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NXP TPMS SENSITIVITY DIFFERENCE BETWEEN FXTH87 AND FXTH87E BL SENSORS NOV 2017 CONFIDENTIAL AND PROPRIETARY
FXTH87E: modification of the sensors transfer functions 1/3 FXTH87E FXTH87 Tolerance = Over-flow 510 510 9-bit 9-bit Usable Range Usable Range 1 1 Tolerance = Under-flow Rated max Pressure, Accelerometer Rated max Pressure, Accelerometer Rated min Pressure, Accelerometer Rated min Pressure, Accelerometer Tolerances may fall outside of Usable Range Tolerances contained within the Usable Range 1 CONFIDENTIAL AND PROPRIETARY
FXTH87E: modification of the sensors transfer functions 2/3 Sensitivity difference between 87 and 87E for pressure and acceleration: illustration with 900kPa range pressure, -40 C < Ta < 125 C, typical values Overflow or underflow 87E 87 output of output of Actual pressure [kPa] TPMS_COMP_PRESSURE [counts] TPMS_COMP_PRESSURE [counts] In-range 510 900 510 493 87 sensitivity = 900??? 100??? = 1.572???/????? 510 1 87E sensitivity = 900??? 100??? = 1.684???/????? 493 18 256 256 500 18 1 100 1 2 CONFIDENTIAL AND PROPRIETARY
FXTH87E: modification of the sensors transfer functions 3/3 If the customer application software contains fixed values for thresholds, these fixed values will need to be adjusted for the FXTH87E sensor. For example if the FXTH87 software used 68 counts to represent a desired 8g s in order to determine that the wheel is rolling, the FXTH87E sensor would need 10g s before the same 68 counts would be reached. As a second example, the count value for 140kPa in the FXTH87 sensor would be 64 counts, which might be used to generate a warning that the pressure had dropped below the legislated minimum level. Those same 64 counts in the FXTH87E sensor would equate to 207.5kPa. In both cases, the customer would have to account for the adjusted sensitivities to recalculate the binary count values for any fixed target thresholds, and then everything else is the same. 3 CONFIDENTIAL AND PROPRIETARY
