Accelerometer

Behavioral model of MEMS accelerometer

Library

Sensors

Description

The Accelerometer block implements a behavioral model of a MicroElectroMechanical Systems (MEMS) accelerometer. For the default output type Voltage level, the accelerometer provides an output voltage that is proportional to the acceleration rate presented at the mechanical translational physical port R. The output voltage is limited according to the values that you provide for maximum and minimum output voltage.

The block also has an alternative output type, PWM duty cycle. With this choice, the output of the block is a PWM signal with a duty cycle that is proportional to the measured acceleration. You can limit the variation in duty cycle to a specified range.

Optionally, you can model sensor dynamics by setting the Dynamics parameter to Model sensor bandwidth. Including dynamics adds a first-order lag between the angular rate presented at port R and the corresponding voltage applied to the electrical + and - ports.

If running your simulation with a fixed-step solver, or generating code for hardware-in-the-loop testing, MathWorks recommends that you set the Dynamics parameter to No dynamics — Suitable for HIL, because this avoids the need for a small simulation time step if the sensor bandwidth is high.

Dialog Box and Parameters

Output type

Select one of the following options to define the block output type:

  • Voltage level — The amplitude of the output voltage is proportional to the measured acceleration. This is the default option.

  • PWM duty cycle — The duty cycle (on time divided by the pulse total time) is proportional to the measured acceleration.

Sensitivity

The change in output voltage level per unit change in acceleration when the output is not being limited. This parameter is only visible when you select Voltage level for the Output type parameter. The default value is 1000 mV/gee.

Output voltage for zero acceleration

The output voltage from the sensor when the acceleration is zero. This parameter is only visible when you select Voltage level for the Output type parameter. The default value is 2.5 V.

Maximum output voltage

The maximum output voltage from the sensor, which determines the sensor maximum measured positive acceleration. This parameter is only visible when you select Voltage level for the Output type parameter. The default value is 4 V.

Minimum output voltage

The minimum output voltage from the sensor, which determines the sensor maximum measured negative acceleration. This parameter is only visible when you select Voltage level for the Output type parameter. The default value is 1 V.

Duty cycle sensitivity (percent per unit acceleration)

The change in duty cycle per unit acceleration. Duty cycle is expressed as a percentage of the PWM period. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 10 percent/gee.

Duty cycle for zero acceleration (percent)

The duty cycle output by the sensor when the acceleration is zero. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 50%.

Maximum duty cycle (percent)

The maximum duty cycle output by the sensor. Increasing acceleration levels beyond this point will not register an increase in duty cycle. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 75%.

Minimum duty cycle (percent)

The minimum duty cycle output by the sensor. Decreasing acceleration levels beyond this point will not register a decrease in duty cycle. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 25%.

PWM frequency

The frequency of the output pulse train. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 1 kHz.

Output voltage amplitude

The amplitude of the output pulse train when high. This parameter is only visible when you select PWM duty cycle for the Output type parameter. The default value is 5 V.

Dynamics

Select one of the following options for modeling sensor dynamics:

  • No dynamics — Suitable for HIL — Do not model sensor dynamics. Use this option when running your simulation fixed step or generating code for hardware-in-the-loop testing, because this avoids the need for a small simulation time step if the sensor bandwidth is high. This is the default option.

  • Model sensor bandwidth — Model sensor dynamics with a first-order lag approximation, based on the Bandwidth and the Initial angular rate parameter values.

Bandwidth

Specifies the 3dB bandwidth for the measured acceleration assuming a first-order time constant. This parameter is only visible when you select Model sensor bandwidth for the Dynamics parameter. The default value is 3 kHz.

Initial acceleration

Determines the initial condition for the lag by specifying the initial output for the sensor, expressed in units of acceleration. This parameter is only visible when you select Model sensor bandwidth for the Dynamics parameter. The default value is 0 gee.

Ports

The block has the following ports:

R

Mechanical translational port

+

Positive electrical port

-

Negative electrical port

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