Inertial navigation principle (VII) -imu error classification (II) -allan variance analysis method +imu test + calibration introduction

List of articles

• Allan Analysis of variance method
• Allan variance – Error model identification case
• Testing and calibration
• • test
  • calibration
  • Other tests and calibrations
  • Classic description
• IMU Calibration of
• • Available reference sources
  • Method :
  • Equipment required :

Allan Analysis of variance method

according to Allan The shape recognition of standard deviation curve is mainly random error , meter
Calculate the model parameters of random error

1. Above picture , The horizontal axis is the time scale , The vertical axis is Allan The square root of variance , Referred to as Allan The standard deviation is also OK ; For the sake of graphic expressiveness , Is a double logarithm curve
2. The white noise is the slope in the figure is -1/2 The straight line of ; The first-order Gaussian Markov process consists of Correlated Noise and Sinusoidal Place performance .Correlated Noise A curve in the shape of a hill , If there is something periodic in the signal , Then it must be from Sinusoidal Reflect the sequence of peaks one after another , It means it's a periodic term ; The flat part is flicker noise , Zero bias instability ; If there is divergence error , It's like random walk , Then it is shown in the figure +1/2 Curve of slope ; Suppose there is a problem with the sensor , The sensor has a linear divergence with zero bias over time , So there's one +1 A straight line with a slope ; If there is quantization noise , Then it shows a slope of -1 The straight line of , But in terms of current sensors , This part will be very few

Allan variance – Error model identification case

1. There is a curve on the left with a downward trend （ Normally , If there is quantization noise , The curve should rise to the left ）, The more you go to the left, the more you respond to short-term and high-frequency information , Because when testing , A large low-pass filter is added to the output , It attenuates the high-frequency part , So the curve goes down
2.Allan Variance in practical application can only see the main contradiction , Secondary factors may not be seen , This is possible

Testing and calibration

test

test , Is to measure indicators , Check the quality of the sensor

calibration

For systematic errors / Constant error measurement , Then compensate

Other tests and calibrations

Test content

• The static test
• Turntable test
• Temperature test
• Magnetic sensitivity
• Centrifugation test
• Impact test
• Vibration test
• Comprehensive test
• Aging and storage test

calibration

• Zero bias
• The scaling factor
• Quadrature coupling
• Temperature drift
• Acceleration sensitivity *( Additional error of gyro , The gyro should only have diagonal velocity ( Angular motion ) sensitive , But it also affects the acceleration ( Linear velocity ) Also sensitive , This is an error coefficient ), Repeatability can compensate
• Power on process （ start-up 、 preheating ）*

Be careful ： As long as the system error / Constant error , calibration （ compensate ) It makes sense

Classic description

1. All systematic errors can be compensated . But only the main errors are considered . Some random errors can be estimated by navigation algorithm and compensated online .
2. Calibration is the comparison of the instrument output with known reference information , And determine the process output value range of the coefficient that makes the output consistent with the reference information (Chatfield 1997).

IMU Calibration of

1. The initial roll and pitch angles are determined by using accelerometers to sense the earth's gravity , So the zero bias becomes smaller , The accuracy will be higher
2. Gyro bias will affect the determination of the initial heading , So the zero bias becomes smaller , The accuracy will be higher
3. The specific effects can be explained according to the formula

Available reference sources

• Accelerometer : Gravity of the earth
• gyroscope : The earth rotates or the turntable rotates

Method :

• Two positions 、 Six position static test
• Angular rate test

Equipment required :

• Turntable
• Cube