LIS302DL

Mechanical and electrical specifications

9/29

2.4

Terminology

2.4.1

Sensitivity

Sensitivity describes the gain of the sensor and can be determined e.g. by applying 1g

acceleration to it. As the sensor can measure DC accelerations this can be done easily by

pointing the axis of interest towards the center of the earth, noting the output value, rotating

the sensor by 180 degrees (point to the sky) and noting the output value again. By doing so,

±1g acceleration is applied to the sensor. Subtracting the larger output value from the

smaller one and dividing the result by 2 leads to the actual sensitivity of the sensor. This

value changes very little over temperature and also very little over time. The Sensitivity

Tolerance describes the range of Sensitivities of a large population of sensor.

2.4.2

Zero-g level

Zero-g level Offset (Off) describes the deviation of an actual output signal from the ideal

output signal if there is no acceleration present. A sensor in a steady state on a horizontal

surface will measure 0g in X axis and 0g in Y axis whereas the Z axis will measure 1g. The

output is ideally in the middle of the dynamic range of the sensor (content of OUT registers

00h, data expressed as 2’s complement number). A deviation from ideal value in this case is

called Zero-g offset. Offset is to some extent a result of stress to a precise MEMS sensor

and therefore the offset can slightly change after mounting the sensor onto a printed circuit

board or exposing it to extensive mechanical stress. Offset changes little over temperature,

see “Zero-g level change vs. temperature”. The Zero-g level of an individual sensor is stable

over lifetime. The Zero-g level tolerance describes the range of Zero-g levels of a population

of sensors.

2.4.3

Self Test

Self Test allows to check the sensor functionality without moving it. The Self Test function is

off when the self-test bit of ctrl_reg1 (control register 1) is programmed to ‘0‘. When the self-

test bit of ctrl_reg1 is programmed to ‘1‘ an actuation force is applied to the sensor,

simulating a definite input acceleration. In this case the sensor outputs will exhibit a change

in their DC levels which is related to the selected full scale through the device sensitivity.

When Self Test is activated, the device output level is given by the algebraic sum of the

signals produced by the acceleration acting on the sensor and by the electrostatic test-force.

If the output signals change within the amplitude specified inside Table 2, than the sensor is

working properly and the parameters of the interface chip are within the defined

specification.