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      No AvatarKelly01

      MEMS gyroscope is a kind of inertial sensor for measuring angular velocity or angular displacement. It has a wide application prospect in oil logging, weapon guidance, aerospace, mining, surveying and mapping, industrial robot and consumer electronics. Due to the different accuracy requirements in various fields, MEMS gyroscopes are divided into three levels in the market: navigation level, tactical level and consumer level.

      This paper will introduce the navigation MEMS gyroscope in detail and compare their parameters. The following will be elaborated from the technical indicators of MEMS gyro, the drift analysis of gyro and the comparison of three navigation-grade MEMS gyro.

      Technical specifications of MEMS gyroscope

      The ideal MEMS gyroscope is that the output of its sensitive axis is proportional to the input angular parameters (Angle, angular rate) of the corresponding axis of the carrier under any conditions, and is not sensitive to the angular parameters of its cross axis, nor is it sensitive to any axial non-angular parameters (such as vibration acceleration and linear acceleration). The main technical indicators of MEMS gyroscope are shown in Table 1.

      Technical indicator Unit Meaning
      Measuring range (°)/s Effectively sensitive to the range of input angular velocity
      Zero bias (°)/h The output of a gyroscope when the input rate in the gyroscope is zero. Because the output is different, the equivalent input rate is usually used to represent the same type of product, and the smaller the zero bias, the better; Different models of products, not the smaller the zero bias, the better.
      Bias repeatability (°)/h(1σ) Under the same conditions and at specified intervals (successive, daily, every other day…) The degree of agreement between the partial values of repeated measurements. Expressed as the standard deviation of each measured offset. Smaller is better for all gyroscopes (evaluate how easy it is to compensate for zero)
      Zero drift (°)/s The rate of time change of the deviation of the gyroscope output from the ideal output. It contains both stochastic and systematic components and is expressed in terms of the corresponding input angular displacement relative to inertial space in unit time.
      Scale factor V/(°)/s、mA/(°)/s The ratio of the change in the output to the change in the input to be measured.
      Bandwidth Hz In the frequency characteristic test of gyroscope, it is stipulated that the frequency range corresponding to the amplitude of the measured amplitude is reduced by 3dB, and the precision of the gyroscope can be improved by sacrificing the bandwidth of the gyroscope.
      Table 1 Main technical indexes of MEMS gyroscope

      Drift analysis of gyroscope

      If there is interference torque in the gyroscope, the rotor shaft will deviate from the original stable reference azimuth and form an error. The deviation Angle of rotor axis relative to inertial space azimuth (or reference azimuth) in unit time is called gyro drift rate. The main index to measure the accuracy of gyroscope is the drift rate.

      Gyroscopic drift is divided into two categories: one is systematic, the law is known, it causes regular drift, so it can be compensated by computer; The other kind is caused by random factors, which causes random drift. The systematic drift rate is expressed by the angular displacement per unit time, and the random drift rate is expressed by the root mean square value of the angular displacement per unit time or the standard deviation. The approximate range of random drift rates of various types of gyroscopes can be reached at present is shown in Table 2.

      Gyroscope type Random drift rate/(°)·h-1
      Ball bearing gyroscope 10-1
      Rotary bearing gyroscope 1-0.1
      Liquid float gyroscope 0.01-0.001
      Air float gyroscope 0.01-0.001
      Dynamically tuned gyroscope 0.01-0.001
      Electrostatic gyroscope 0.01-0.0001
      Hemispherical resonant gyroscope 0.1-0.01
      Ring laser gyroscope 0.01-0.001
      Fiber optic gyroscope 1-0.1
      Table 2 Random drift rates of various types of gyroscopes

      The approximate range of random drift rate of gyro required by various applications is shown in Table 3. The typical index of positioning accuracy of inertial navigation system is 1n mile/h(1n mile=1852m), which requires the gyroscope random drift rate should reach 0.01(°)/h, so the gyroscope with random drift rate of 0.01(°)/h is usually called inertial navigation gyroscope.

      Application Requirements for random drift rate of gyro/(°)·h-1
      Rate gyroscope in flight control system 150-10
      Vertical gyroscope in flight control system 30-10
      Directional gyroscope in the flight control system 10-1
      Tactical missile inertial guidance system 1-0.1
      Marine gyro compass, strapdown heading attitude system artillery lateral position, ground vehicle inertial navigation system 0.1-0.01
      Inertial navigation systems for aircraft and ships 0.01-0.001
      Strategic missile, cruise missile inertial guidance system 0.01-0.0005
      Table 3 Requirements for random drift rate of gyro in various applications

      Comparison of three navigation-grade MEMS gyroscopes

      Ericco’s MG2 series is a navigation-grade MEMS gyroscope with a high level of accuracy to meet the needs of various fields. The following table compares range, bias instability, angular random walk, bias stability, scale factor, bandwidth, and noise.

      ER-MG2-50/100 ER-MG2-200 ER-MG2-300/400
      Measuring range(deg/s) 50-100 200 300-400
      Bias instability(deg/hr) 0.01-0.02 0.02 0.03-0.05
      Angular Random Walk(°/√h) 0.0025-0.005 0.005 0.01-0.025
      Bias stability(1σ 10s)(deg/hr) 0.05-0.1 0.1 0.15-0.5
      Bias stability(1σ 1s)(deg/hr) 0.15-0.3 0.3 0.5-1.5
      Scale factor(lsb/deg/s) 160000-80000 40000 28000-20000
      Bandwidth(-3dB)(Hz) 12 50 50-100
      Noise peak to peak(deg/s) ±0.002~±0.003 0.04 ±0.01~±0.05
      Table 4 Parameter comparison table of three navigation-grade MEMS gyroscopes

      As can be seen from Table 4, the biggest difference between the three gyroscopes lies in their different ranges. Compared with ER-MG2-100, the accuracy level remains unchanged, but the range is expanded to 200deg/s, which makes the measurement range larger, can meet higher requirements, and is more applicable. The first two are MEMS North finding gyroscopes, while the ER-MG2-300/400 is a MEMS navigation gyroscope for air and sea navigation.

      I hope that through this article, you can understand the technical indicators of navigation-grade MEMS gyroscope and the comparative relationship between them. If you are interested in more knowledge about MEMS gyro, please discuss with us.

      Comparison Of Technical Specifications Of Navigation Grade MEMS Gyroscope

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