According to the application background of a project, a strapdown inertial measurement unit (FOG Inertial Measurement Unit) is designed and implemented with open-loop fiber optic gyro and silicon micro-accelerometer as inertial sensing components and high-speed DSP as signal processor. The system implements the basic function of sending out angular velocity information and specific force information every 10 ms. Considering the operating characteristics of the system, corresponding measures are taken in the design of software and hardware of the system to ensure the accuracy of the system, improve the real-time performance of the system, and expand the system function. Finally, the system is tested, and the results show that the system has reached the expected design goal.

The inertial navigation system can measure the carrier's heading, attitude and position in real time. Compared with the platform inertial navigation system, the strapdown inertial navigation system replaces the electromechanical physical platform with the "mathematical platform" stored in the computer. The measurement data of the gyroscope and accelerometer are collected by the computer, and the information such as the position, attitude and heading of the carrier is obtained through solving, which is used for the control and navigation of the carrier.

Compared with the traditional flexible gyro, the optical fiber gyro has the advantages of anti-impact and anti-acceleration, short start-up time, high sensitivity and resolution, wide dynamic range, low price, etc., which is suitable for the use in harsh environment, because it is more suitable for the construction of strapdown inertial measurement unit.
Fiber optic gyro strapdown inertial navigation system has become one of the most important development directions in many fields such as aerospace, aviation, maritime and land navigation. At present, fiber optic gyroscopes have obvious advantages in the application range of medium and low precision (0.01 ~ 30 ° / h). Mems-based silicon micro-accelerometers have also been able to achieve 10-3 g or even higher accuracy, and the volume is very small, easy to integrate the system. The strapdown inertial measurement unit using fiber optic gyroscope(FOG Inertial Measurement Unit) and silicon microaccelerometer has the advantages of low cost and small size, and has broad application prospects in both military and civil fields.

1 Overall design of the system
According to the overall requirements of the system, the inertial device selection and system structure design are carried out. Through the error transfer equation of strapdown inertial navigation system, the error analysis and computer simulation results show that the open-loop fiber optic gyro and silicon micro-accelerometer with low precision can meet the requirements of the system index.
The system consists of mechanical structure, three fiber optic gyroscopes, accelerometer components and processing circuit. In the structural design, the sensitive axes of the tourmala components are mutually orthogonal; The accelerometer component composed of 3 circuit boards ensures that the 3 sensitive axes are vertically intersected with the space point during PCB design; The non-orthogonal error of the system can be compensated by software through calibration.

2 Data acquisition module
The data acquisition module mainly completes the functions of sampling, analog filtering, amplifying and modulo conversion of the output signals of 3 doloris and 3 accelerometers. In order to improve the acquisition accuracy of the inertial measurement unit, the pre-processing circuit of the inertial device is designed. The gyro and accelerometer outputs are converted into single-ended and unipolar voltages by two-stage op amp and analog filter, and then A /D conversion is performed. The module collects 8 analog signals, in addition to 3 gyro signals and 3 accelerometer signals, accelerometer chip temperature and ambient temperature are also collected for temperature compensation.

FOG Inertial Measurement Unit Data Acquisition System A D convert

3 Summary
In this paper, the open loop optical fiber toralon and silicon micro-accelerometer are used as inertial devices to design and implement the inertial measurement unit which is applied to the medium and low precision and short time operating system. It can be seen that the data acquisition system has reached the performance index specified in the medium-precision strapdown inertial navigation system. At present, the system has been used in some prototypes of strapdown inertial navigation system and runs well. Ericco has several cost-effective, low-cost FOG inertial measurement units ER-FIMU-50, ER-FIMU-60, ER-FIMU-70, if you want to get more technical data of FOG inertial measurement units, please feel free to contact us.