SM9233/SM9235/SM9236 Series www.si-micro.com27
13. Functional Description45 131
13.1 OverviewThe SM9x3x series is a high precision, factory calibrated Gauge pressure sensor for ultra low pressure measurements. It combines a low pressure MEMS die with a 16 bit ASIC, utilizing DSP for multi dimensional polynomial error correction. The calibrated pressure output data 167 is available via digital data interface (I2C). Status information on the sensor integrity and unique serial number are accessible via this 170 digital interface. 175
13.2 Global Sensor Parameters169
13.2.1 Digital Pressure Transfer Function0 In general digital output data is available with a word length of 16 bit. The numeric representation is always as 2's complement, which 61 results in a range of: 0 ... +32767 counts (positive range, or 0000h ... 7FFFh) -32768 ... -1 counts (negative range, or 8000h ... FFFFh) The pressure sensor device is calibrated in the end-of-line production test over the specified Pmin to Pmax pressure range (see Section 4). The output code at Pmin is nominally -26,215 and at Pmax it is nominally 26,214. This allows the sensor to still operate monotically outside its nominal range till the maximum (or minimum) counts are reached. An example for a 250 Gauge SM9233-BCE-S-250-000 is given in the graph below
Green:Accuracy per specification
Redand
Blue: Outside specification, but expect monotonic behavior till maximum (or minimum) code is reached
13.2.2 Conversion from counts to pressureThe digital output count gives a signed 16 bit value for pressure and to convert the count to a pressure percent reading, p%FS, (in % full scale pressure) the following equation can be used The equation below converts p%FS to actual calibrated pressure units pp-unit with pmin and pmax as specified in section 4 Silicon Microstructures, Inc. 2001-2019. All rights reserved +1-(408) 577-0100 |
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