MPXM2102AS datasheet(349/670 Pages) MOTOROLA

349 / 670 page

3–203

Motorola Sensor Device Data

www.motorola.com/semiconductors

AN1097

Calibration-Free Pressure Sensor System

Prepared by: Michel Burri, Senior System Engineer

Geneva, Switzerland

INTRODUCTION

The

MPX2000

series

pressure

transducers

are

semiconductor devices which give an electrical output signal

proportional to the applied pressure. The sensors are a single

monolithic silicon diaphragm with strain gauge and thin–film

resistor networks on the chip. Each chip is laser trimmed for

full scale output, offset, and temperature compensation.

The purpose of this document is to describe another method

of measurement which should facilitate the life of the designer.

The MPX2000 series sensors are available both as unported

elements and as ported assemblies suitable for pressure,

vacuum and differential pressure measurements in the range

of 10 kPa through 200 kPa.

The use of the on–chip A/D converter of Motorola’s

MC68HC05B6 HCMOS MCU makes possible the design of

an accurate and reliable pressure measurement system.

SYSTEM ANALYSIS

The measurement system is made up of the pressure

sensor, the amplifiers, and the MCU. Each element in the

chain

has

its

own

device–to–device

variations

and

temperature effects which should be analyzed separately. For

instance, the 8–bit A/D converter has a quantization error of

about

±0.2%. This error should be subtracted from the

maximum error specified for the system to find the available

error for the rest of elements in the chain. The MPX2000 series

pressure sensors are designed to provide an output sensitivity

of 4.0 mV/V excitation voltage with full–scale pressure applied

or 20 mV at the excitation voltage of 5.0 Vdc.

An interesting property must be considered to define the

configuration of the system: the ratiometric function of both the

A/D converter and the pressure sensor device. The

ratiometric function of these elements makes all voltage

variations from the power supply rejected by the system. With

this advantage, it is possible to design a chain of amplification

where the signal is conditioned in a different way.

+ Vs

PIN 3

Rs1

PIN 2

–

PIN 4

Vout

Rin

Rs2

PIN 1

GND

THERMISTOR

LASER

TRIMMED

ON–CHIP

Figure 1. Seven Laser–Trimmed Resistors and Two

Thermistors Calibrate the Sensor for Offset, Span,

Symmetry and Temperature Compensation

The

amp

configuration

should

have

good

common–mode rejection ratio to cancel the DC component

voltage of the pressure sensor element which is about half the

excitation voltage value VS. Also, the op amp configuration is

important when the designer’s objective is to minimize the

calibration procedures which cost time and money and often

don’t allow the unit–to–unit replacement of devices or modules.

One other aspect is that most of the applications are not

affected by inaccuracy in the region 0 kPa thru 40 kPa.

Therefore, the goal is to obtain an acceptable tolerance of the

system from 40 kPa through 100 kPa, thus minimizing the

inherent offset voltage of the pressure sensor.

MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

REV 1

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MPXM2102AS датащи(PDF) 349 Page - Motorola, Inc

MPXM2102AS датащи(HTML) 349 Page - Motorola, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL