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## ADXL05 Datasheet(HTML) 6 Page - Analog Devices

 6 / 20 pageADXL05REV. B–6–package. Figure 2c describes a three dimensional accelerationvector (AXYZ) which might act on the sensor, where AX is thecomponent of interest. To determine AX, first, the componentof acceleration in the XY plane (AXY) is found using the cosinelaw:AXY = AXYZ (cosθXY) thenAX = AXY (cosθX)Therefore: Nominal VPR = 200 mV/g (AXYZ) (cosθXY) cosθXAxyz–Z AXISX AXISY AXISAxyAxθxyθxFigure 2c. A Vector Analysis of an Acceleration ActingUpon the ADXL05 in Three DimensionsNote that an ideal sensor will react to forces along or at anglesto its sensitive axis but will reject signals from its various trans-verse axes, i.e., those exactly 90° from the sensitive “X” axis.But even an ideal sensor will produce output signals if the trans-verse signals are not exactly 90° to the sensitive axis. An accel-eration that is acting on the sensor from a direction differentfrom the sensitive axis will show up at the ADXL05 output at areduced amplitude.Table I shows the percentage signals resulting from variousθXangles. Note that small errors in alignment have a negligibleeffect on the output signal. A 1° error will only cause a 0.02%error in the signal. Note, however, that a signal coming 1° off ofthe transverse axis (i.e., 89° off the sensitive axis) will still con-tribute 1.7% of its signal to the output. Thus large transversesignals could cause output signals as large as the signals ofinterest. Table I may also be used to approximate the effect ofthe ADXL05’s internal errors due to misalignment of the die tothe package. For example: a 1 degree sensor alignment error willallow 1.7% of a transverse signal to appear at the output.Table I. Ideal Output Signals for Off Axis AppliedAccelerations Disregarding Device Alignment andTransverse Sensitivity Errors% of Signal AppearingOutput in gs for a 5 gθXat OutputApplied Acceleration0100%5.000 (On Axis)1°99.98%4.9992°99.94%4.9973°99.86%4.9935°99.62%4.98110°98.48%4.92430°86.60%4.33045°70.71%3.53660°50.00%2.50080°17.36%0.86885°8.72%0.43687°5.25%0.26388°3.49%0.17589°1.7%0.08590°0%0.000 (Transverse Axis)Mounting Fixture ResonancesA common source of error in acceleration sensing is resonanceof the mounting fixture. For example, the circuit board that theADXL05 mounts to may have resonant frequencies in the samerange as the signals of interest. This could cause the signalsmeasured to be larger than they really are. A common solutionto this problem is to dampen these resonances by mounting theADXL05 near a mounting post or by adding extra screws tohold the board more securely in place.When testing the accelerometer in your end application, it isrecommended that you test the application at a variety of fre-quencies in order to ensure that no major resonance problemsexist (refer to Analog Devices Application Note AN-379).10901000%0.5msFigure 3. 500 g Shock Overload Recovery. Top Trace, PCBReference Accelerometer Output: 500 g/Vertical Division.Bottom Trace, ADXL05 Output at VPROBSOLETE