What can Fiber Optic Gyroscopes be Used for?

 

1.What is a fiber optic gyroscope?

A fiber optic gyroscope (FOG) is a device used to measure angular velocity and direction. It provides extremely accurate rotational speed information with low maintenance costs and long service life.
Fiber optic gyroscopes are becoming more affordable, and the technology has proven beneficial for an ever-expanding array of different high-performance inertial navigation systems (INS). As a result, FOG has become the default choice for strategic and tactical level applications that require long-term navigation in environments where GNSS (Global Navigation Satellite System) is not available.

2.How does a fiber optic gyroscope work?

Fiber optic gyroscopes use the properties of light in closed circuits to estimate changes in direction. Two beams of light are sent in opposite directions in the fiber coil.
As the vehicle rotates, the beam traveling against the rotation experiences a slightly shorter path delay than the other beams, a phenomenon known as the Sagnac effect. The phase shift difference between the two beams is then used to estimate the rotation rate.

3.What is the difference between a ring laser gyroscope and a fiber optic gyroscope?

Similar to the FOG, the ring Laser gyroscope (RLG) is an optical gyroscope that utilizes the Sagnac effect. The main difference between the two is the way they are constructed, because a ring laser gyroscope uses a laser passing through a system of mirrors to determine the rotation of the vehicle, rather than a simple fiber optic coil.
In addition to requiring extremely high manufacturing precision and special mirrors, the RLG is also filled with gas, and the laser needs to be "dithered," or mechanically vibrated, to prevent laser locking to eliminate small rotations.
While both types of gyroscopes work similarly and are very accurate, the older toroidal laser gyroscope technology is more sophisticated due to its construction, requires more maintenance, and is generally more expensive. In contrast, the fiber optic gyroscope is a solid-state device that does not use a jitter mechanism, which means it does not produce any acoustic vibrations, making it more durable and reliable than the RLG. In addition, the application of fiber optic gyroscopes can be extended by changing the length and diameter of the fiber optic coils.

4.What is the difference between a fiber optic gyroscope and a MEMS gyroscope?

A MEMS (Micro-electro-mechanical System) gyroscope is a smaller, lighter gyroscope made from tiny devices. MEMS gyroscopes have significantly reduced SWaP-C, which means they are preferred for applications requiring small payloads.
FOG has higher inertial performance and lower deviation, making it the preferred solution for high-precision applications such as GNSS rejection environments or antenna pointing.

5.What can fiber optic gyroscopes be used for?

Fiber optic gyroscope technology facilitates a growing number of applications where accurate heading and navigation are critical. This includes both manned and driverless vehicles.
Surface Ocean Vehicles: Ocean survey vessels use fiber optic gyroscopes to determine pitch, roll, and heading in real time and build accurate position data for unmanned underwater vehicles (UUV). They are particularly useful for side-scan sonar and similar applications.
Undersea vessels: Manned vehicles (such as submarines) and UUVs (unmanned underwater vehicles), including autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs), rely on fiber-optic gyroscopes for precise navigation in extremely challenging and dangerous environments at minimal cost. Or an unreliable source of absolute location. Rovs and AUVs for hydrology in particular benefit from FOG's precision.
Aviation: Helicopters can be subject to electromagnetic interference and can benefit greatly from FOG-based INS. Unmanned aerial vehicles (UAVs) and commercial aircraft typically require FOG-level performance to reduce the risk of losing GNSS locations while in flight. The accuracy of roll, pitch and yaw data is critical to the safe operation of the aircraft.
Defense: Ground-based defense vehicles must not rely on GPS/GNSS because of the risk of local interference or spoofing of these signals, or simply the risk of terrain blocking or altering satellite positioning data. Fibre-based INS allows these vehicles to operate seamlessly, preventing adversaries from gaining an advantage from these tactics.
Space exploration: Fiber optic gyroscopes are ideal for space applications due to their long service life, virtually maintenance-free, extremely low power consumption, and accurate navigation data.
Robotics: Directional data from the fiber optic gyroscope is used to navigate the robot, ensuring safe operation when adjusting for any changes in speed, position or acceleration.
Ericco's ER-FOG-50, ER-FOG-60 small size, light weight, the use of digital closed loop mode, no wear parts, long service life, a wide range of applications, is our good choice, if you are interested in our products, please feel free to contact us.

Who Makes Fiber Optic Gyroscopes?

 

1.The use of gyroscopic technology

For more than 100 years, gyroscopic technology has been used to aid navigation in a variety of applications. Mechanical gyroscopes were relied upon for about 60 years until the invention of the ring laser gyroscope in the 1960s. However, it wasn't until the 1970s that fiber optic gyroscopes were developed, implemented, and became popular in a wide range of applications from submarines to spacecraft.
The goal of any gyroscope is to measure the angular rotation rate on any single axis. This is critical for determining the pitch, roll, and yaw angles in a system that requires reliable navigation information to function properly. Imagine a plane taking off, a NASA rocket diving, or a missile finding its target. Gyroscopes for such applications measure the angular rotation rate of each vehicle. This critical information is sent downstream to control and stabilize the vehicle. Each gyroscope provides this information with varying degrees of reliability and accuracy, so how does a fiber optic gyroscope differ from other gyroscopes?

2.Optical fiber technology

As the name suggests, fiber optic gyroscopes use fiber optics to perform their work. Fiber optics are made of glass and are used in many applications to transmit light from one point to another. Fiber optic cables are commonly used in telecommunications such as telephones and the Internet, and are extremely fast and reliable.

In a fiber optic gyroscope, this method of light transmission is not used to transmit information elsewhere, but is tightly wound in an independent closed loop within the gyroscope. This allows the fiber optic gyroscope to take advantage of the "Sagnac effect."

3.Sagnac effect

This phenomenon, discovered by French physicist Georges Sagnac, is at the heart of how every fiber optic gyroscope works.
Inside the gyroscope, the laser is used to send two separate beams of light through an optical fiber. Each beam travels in the opposite direction, propagating the entire length of the fiber, up to 5 kilometers. Each beam then returns to the light detector, recording its travel time.
Take an international flight at cruising altitude. The aircraft is stable, flying straight, level, with no rotation changes.
When there is no rotation change in the aircraft, the beam returns to the detector at the same time. In this case, there is no delay or "phase shift" between each beam. The aircraft was detected as stable and did not undergo any rotation rate around any given axis.
However, when the plane turns, Sagnac will come into full play. When the aircraft turns to the right, the fiber optic gyroscope dedicated to the rolling shaft will experience an arrival delay between the two beams. As it rotates, the distance each beam must travel changes.
When the detector is slightly closer to the traveling beam, the light traveling against the direction of rotation will return first. In this example, the beam propagating to the left will return first. Similarly, a beam traveling to the right will take longer. The phase shift between each beam is detected as a rotational change. This critical information can then be sent downstream to an aircraft, spacecraft, submarine or missile to stabilize it. This happens at a rate of hundreds of times per second, providing very precise measurements.

4.Fiber optic gyroscope calibration

As with any gyroscope, error sources, deviations, and noise must be carefully considered and corrected. During manufacturing, fiber optic gyroscopes are calibrated to correct for several potential sources of error that can be introduced by the gyroscope itself or the environment. When calibrated, fiber optic gyroscopes provide a very high level of performance.
Why use fiber optic gyroscopes?
Fiber optic gyroscopes have become ubiquitous in many applications, with several attractive properties. They remain reliable in harsh environments with intense vibration, have no moving parts, strike a good balance between price and high performance, and can last a long run.

5.Summary

Ericco developed fiber optic gyroscope ER-FOG-851, ER-FOG-910, low cost, good performance, can be widely used in optical pod/flight control level, INS/IMU, platform stabilization device, positioning system, north finder, high precision measurement/navigation system and servo system, if you are interested in learning more, Please feel free to contact us.

IMU Calibration Using 12-position Method

 

Introduce

The 12-point calibration is a method used for the calibration of the Inertial Measurement Unit (IMU). IMU is a device that can measure the acceleration and angular velocity of an object and is widely used in aerospace, navigation, robotics and other fields. In practical applications, the accuracy of IMU is crucial to the accuracy and reliability of measurement results. Therefore, it is essential to correct the IMU error through calibration.

 

The 12-position method is a calibration method based on position changes. Its principle is to use mathematical models to calculate the error parameters of the IMU by recording the output data of the IMU at different positions and postures. Specific steps are as follows:

 

The first step is to determine the position: During the calibration process, a series of different positions and postures need to be selected. These positions should cover the entire measurement space as much as possible, and it is necessary to ensure that the output data of the IMU at these positions is reliable and accurate.

 

The second step is to collect data: At each position and attitude, fix the IMU on the object and collect the output data of the IMU. These data include accelerometer and gyroscope measurements. In order to improve the measurement accuracy, it is usually necessary to repeat the measurement multiple times and average it.

 

The third step is to establish a mathematical model: use the collected data to establish an IMU error model. This model can be solved through mathematical methods such as linear regression and least squares method. According to the parameters solved by the model, the output data of the IMU can be corrected.

 

The fourth step is to calculate the error parameters: According to the mathematical model, calculate the error parameters of the IMU. These parameters include zero bias, scale factor, non-orthogonality, etc. These parameters can be used to correct the output data of the IMU and improve the accuracy and precision of the measurement.

 

The fifth step is to verify the calibration results: The accuracy and reliability of the calibration results need to be verified. Some known accurate measurements can be used to compare the calibrated measurement results to ensure the validity of the calibration.

 

IMU calibration method using 12-position method

 

As a commonly used IMU calibration method, the 12-position method has the following advantages:

1.High accuracy: By performing calibration at different positions and postures, the error characteristics of the IMU can be more comprehensively considered and the accuracy and precision of the measurement can be improved.

 

2.Strong reliability: By repeating measurements multiple times and averaging, the impact of random errors can be reduced and the reliability of the calibration results can be improved.

 

3.Wide scope of application: The 12-position method is suitable for various types of IMUs, whether it is MEMS (Micro-Electro-Mechanical Systems) or fiber optic gyroscopes, etc.

 

4.Simple operation: The 12-position method does not require complex equipment and experimental conditions. It only needs to fix the IMU in different positions and postures for measurement.

 

However, the 12-position method also has some limitations:

 

1.It takes a long time: Since measurements need to be performed at multiple positions and postures, the calibration process is cumbersome and takes a long time.

 

2.High requirements for the test environment: Since the output of the IMU is affected by environmental factors, such as temperature, humidity, etc., the calibration process needs to be carried out in a well-controlled experimental environment.

 

Summarize

As a commonly used IMU calibration method, the 12-position method can effectively improve the accuracy and reliability of IMU measurement results. In practical applications, it is very important to select a suitable calibration method for IMU calibration based on specific needs and experimental conditions. Through calibration, the error of the IMU can be corrected and the accuracy of measurement can be improved to better meet the needs of practical applications. The MEMS IMU independently developed by Ericco has built-in gyroscopes and accelerometers. They have relatively high accuracy and can be used in many fields. For example, ER-MIMU-01 and ER-MIMU-05, welcome to learn more.

Why and Where are Tilt Sensors Used

 

1. Why do people monitor tilt angles?

The world is constantly changing, and the tendencies of different objects and machines can provide insight into worrying trends and potential future problems. There are many reasons why people need to monitor the Angle or degree of inclination.

Avoid accidents and injuries
One reason is that it can help prevent injuries and avoid accidents. When people work on the slope, they need to pay attention to the Angle of the slope to ensure that they do not slip. If the Angle is too steep, it can cause an avalanche, which is very dangerous.

Ensure the normal operation of the device
Another reason to monitor the tilt Angle, or tilt, is to make sure the equipment is working properly. For example, if a machine is not level, it may not work properly. This can be dangerous for the person using the device and the people around it.

2. Where can the tilt sensor be used?

Tilt sensors can be used in many applications, such as the Marine industry, construction industry, infrastructure monitoring, etc.

Marine industry
Tilt sensors can be used on ships to measure ship roll and pitch. This information can be used to improve the stability of the ship and avoid capsizing.
Construction industry
In many construction machines, such as excavators and bulldozers, tilt sensors can be used to measure the Angle of the machine blade or bucket. This information can be used to automatically adjust the position of the blade or bucket, or to provide feedback to the operator.
Infrastructure monitoring
Tilt sensors can be used to monitor the status of infrastructure such as Bridges and buildings and alert authorities to potential hazards, such as leaning towers. By continuously monitoring the tilt of the structure, the sensors can detect even the smallest changes that could indicate a problem. In the event of a potential accident, sensors can provide critical information that can be used to evacuate people and take other safety measures.
Tree bend monitoring
Some trees may fall after storms, typhoons or other natural disasters. Tilt sensors can be installed at a certain height on these trees to monitor their x, y, and z values in real time. This can provide insights into tree tilt and movement and help make timely, effective decisions to protect trees and people.
Gate monitoring
In car parking lots and parking garages, the normal operation of road gates is crucial to the normal toll collection. The tilt sensor can be installed in the guardrail housing, especially suitable for the guardrail Angle measurement and movement detection, to determine whether the guardrail is dropped, bent or broken, if there is a trigger alarm, so that maintenance personnel can take measures in time. Ensure regular charges.

3. Summary

Ericco's ER-TS-12200-Modbus precision up to 0.001°, the use of advanced Internet of Things technology Bluetooth and ZigBee(optional) wireless transmission technology, all internal circuits are optimized design, using industrial MCU, three-proof PCB board, imported cables, wide temperature metal shell and other measures, Improve the industrial level of products. Good long-term stability, zero drift small, can automatically enter low-power sleep mode, get rid of the dependence on the use of the environment, equipped with IP67-rated housing, so that it can withstand harsh conditions and still work normally. The optimized internal design of multi-layer structure, sealing ring, and three anti-coating further enhances the waterproof and dustproof capability.

The ER-TS-3160VO voltage uniaxial tilt sensor is an analog voltage uniaxial tilt sensor. The user only needs to collect the sensor voltage value to calculate the tilt Angle of the current object. The built-in (MEMS) solid pendulum measures changes in the static gravity field, converts them into changes in inclination, and outputs them via voltage (0~10V, 0.5~4.5V, 0~5V optional). The product adopts the non-contact measurement principle and can output the current attitude and inclination Angle in real time. If you would like more technical data, please feel free to contact us.

IMU calibration method and calibration process

 https://www.ericcointernational.com/application/imu-calibration-method-and-calibration-process.html

1.Introduction and importance of IMU

IMU (Inertial Measurement Unit) is an inertial measurement unit, which is a device used to measure the angular velocity and acceleration of objects in three-dimensional space. The IMU consists of three gyroscopes and three accelerometers, which are used to measure the angular velocity and acceleration of an object on three orthogonal axes. Because IMU can provide continuous attitude and position information, it is widely used in many fields, such as navigation, drones, robots, augmented reality, etc.

 

Accurate calibration of the IMU is of great significance for improving the navigation and positioning accuracy of the system. The calibration process can help us understand the error characteristics of the IMU, and then compensate for it through algorithms to improve measurement accuracy.

 

2.Calibration methods and classification

The calibration methods of IMU are mainly divided into two categories: static calibration and dynamic calibration. Static calibration is mainly used to evaluate the zero bias and scale factor error of the IMU, while dynamic calibration is mainly used to evaluate the nonlinear error and coupling error of the IMU.

 

3.Static calibration method

The static calibration method is usually carried out in a static state. By collecting the static data of the IMU in different directions, its zero bias and scale factor error are calculated. This method is simple and easy to implement, but it cannot evaluate the nonlinear error and coupling error of the IMU.

The main steps of the static calibration method:

 

3.1 Zero offset calibration

3.1.1 Place the IMU on a horizontal platform and keep it stationary to ensure that the IMU is free from external forces.

3.1.2 Record accelerometer and gyroscope output data for a period of time. For three-axis accelerometers and three-axis gyroscopes, the output data on each axis needs to be recorded separately.

3.1.3 For the accelerometer and gyroscope data on each axis, calculate the average. This average value is the zero offset parameter on this axis. The zero offset parameter reflects the output offset of the IMU without external force.

 

3.2 Scaling factor calibration

3.2.1 Place the IMU in a reference system with known acceleration and angular velocity. This reference system can provide accurate acceleration and angular velocity data for comparison with the IMU output data.

3.2.2 Record the output data of the IMU and reference system. These data should include values for acceleration and angular velocity.

3.2.3 Calculate the scale factor parameters based on the known acceleration and angular velocity and the output data of the IMU. The scale factor parameter reflects the proportional relationship between the IMU output value and the actual value.

 

4.Dynamic calibration method

The dynamic calibration method needs to be carried out in a dynamic environment. By collecting the data of the IMU in a moving state, its nonlinear error and coupling error can be evaluated. This method can more comprehensively evaluate the error characteristics of the IMU, but the operation is relatively complex.

 

5.Calibration data processing

Calibration data processing is an important part of the calibration process, which mainly includes data preprocessing, error model establishment, parameter estimation and other steps. Data preprocessing mainly involves filtering and smoothing the original data to reduce the impact of noise. The establishment of the error model is based on the error characteristics of the IMU and selecting an appropriate error model to describe its error behavior. Parameter estimation uses optimization algorithms to solve the parameters in the error model.

 

6.Evaluation of calibration results

The evaluation of calibration results mainly evaluates the calibration effect by comparing the data before and after calibration. Evaluation indicators usually include the root mean square value of error, maximum error, minimum error, etc. If the error after calibration is significantly reduced, it means the calibration is effective.

7.Precautions and Tips

 

When performing IMU calibration, you need to pay attention to the following points:

1. Ensure the calibration environment is stable and avoid external interference.
2. Choose an appropriate calibration method and select an appropriate error model according to actual needs.
3. During the calibration process, keep the IMU in a fixed posture to prevent it from moving or rotating.
4. Calibration data must be sufficient to improve the accuracy of parameter estimation.

Summarize

IMU calibration is widely used in many fields, such as drone navigation, robot positioning, augmented reality, etc. With the development of technology, the accuracy and stability of IMUs continue to improve, and its application scope continues to expand. In the future, with the emergence of new IMU sensors and calibration methods, IMU calibration will be more accurate and efficient, providing strong support for the development of related fields. ERICCO's independently developed product MEMS IMU, such as ER-MIMU-01, accurately calibrates the IMU and improves the navigation and positioning accuracy of the system. If you want to learn about or purchase MEMS IMU, please contact us.

What is the Difference Between MEMS and FOG IMU?

 The IMU (Inertial Measurement Unit) combines accelerometers, gyroscopes, and other sensors such as magnetometers to provide information on the direction, rotation, and motion of objects ranging from smartphones to spacecraft.

The two most common types of IMUs are built around microelectromechanical systems (MEMS) technology and fiber optic gyroscope (FOG) technology. Let's take a look at these two.

1. Fiber Optic Gyroscope (FOG) IMU

As the name suggests, FOG is a type of IMU that uses optical fibers to measure the angular speed or rotation rate of any object.
Due to the low noise of fiber optic gyroscopes, this technology has been widely used in demanding navigation applications.
Fogs are inherently more accurate and stable than MEMS-based systems, which makes them preferred for scenarios where GNSS signals are not available (such as mining and underwater applications) or where GNSS rejection may occur. Another notable feature of FOG is its fast north finding capability. Even if the IMU itself is moving, the FOG IMU can measure the angular rotation of the Earth and achieve a heading in just a few minutes.
FOG gyro compasses have no moving parts, which makes them better able to withstand vibration and shock than MEMS gyro compasses. This means they are well suited for applications that may experience strong vibration levels, such as mining, defense, surface ships and aerospace.

2. Microelectromechanical System (MEMS) IMU

MEMS accelerometers detect linear acceleration and can then be used to calculate speed and distance. MEMS gyroscopes detect rotational motion and are typically used to determine heading and/or attitude (roll and pitch). When the data from the accelerometer and gyroscope are combined over time, the position of the object relative to its starting point can be calculated.
Due to their small size, mainstream manufacturing processes, common materials, and widespread adoption, MEMS IMUs are, on average, smaller, lighter, lower power, and more affordable than their FOG counterparts. However, because MEMS IMUs contain more micromechanical components and are more sensitive to temperature fluctuations, they tend to be less accurate and noisier than their fiber optic counterparts. If accurate location data is needed over an extended period of time, MEMS IMUs are often used in conjunction with GNSS receivers or other sensor technologies that provide supplementary location information.
MEMS IMUs are ideal for situations of low size, weight, power consumption and cost. Applications include mobile phones, vehicle navigation systems, autonomous ground vehicles, flying drones and robotic systems.

3. Here are the main differences between FOG IMU and MEMS IMU:

Technology:
FOG IMU uses a fiber optic gyroscope, using the principle of light interference in the fiber.
MEMS IMU uses MEMS systems with accelerometers and gyroscopes based on micromachining technology.

Working criteria:
FOG IMU measures motion by detecting the phase shift of light in the fiber coil due to rotation.
MEMS IMU utilizes the deflection of microstructure due to acceleration or rotation to measure motion.

Accuracy:
FOG IMU offers higher accuracy and precision than MEMS IMU. This makes them especially useful in cases where users rely on IMUs for long periods of time: accurate systems can calculate a location close to the real one even after a few hours.

Size and shape:
FOG IMUs are typically larger and heavier and are typically used in large systems such as aerospace and defense applications.
MEMS IMUs are smaller and more compact, making them suitable for integration into smaller devices such as consumer electronics.

Cost:
FOG IMU is more expensive due to its higher accuracy, highly specialized internal components, and sophisticated advanced manufacturing processes.
MEMS IMUs are generally more cost effective than FOG IMUs, making them widely used in consumer products.

Energy consumption:
FOG IMU consumes more power, which is less important in applications such as land vehicles and aircraft with readily available power supplies.
MEMS IMUs typically have low power consumption, making them suitable for portable and battery-powered devices.

Applications:
FOG IMU is commonly used in aerospace, defense, Marine navigation, and other high-precision applications, especially in situations where GNSS is not available or reliable, such as underground mining or military environments.
MEMS IMUs can be used in smartphones, gaming devices, drones, and a variety of consumer electronics that require motion sensing.

Robustness:
FOG IMU is more robust and stable, making it better suited for particularly harsh and demanding environments.
MEMS IMUs can be susceptible to environmental factors such as extreme temperatures and high vibration, which can affect their accuracy.

Calibration and automatic north finding:
FOG IMUs have better long-term stability and generally require less calibration frequency to maintain accurate heading or position. The most accurate fiber optic gyro systems are so sensitive that they can determine where north is by detecting the Earth's rotation.
Due to the potential for drift over time, MEMS IMUs may require more frequent calibration to maintain accuracy. They are not sensitive enough to automatically find the exact heading unless connected to a GNSS receiver.

Integration:
FOG IMUs are typically used in larger systems that can accommodate their size and weight and meet their higher power needs.
Due to their smaller size and lower power requirements, MEMS IMUs are easier to integrate into compact devices.

Summary
The choice between a MEMS-based IMU and a FOG-based IMU will depend on the customer's specific requirements for size, weight, power and cost (SWaP-C) as well as accuracy and stability needs.
For example, Ericco's FOG IMU ER-FIMU-50 is small in size, ER-FIMU-70 is high in precision, they have a very competitive price, very hot in the market, if you want to get more technical data, please feel free to contact us.

Analysis of strapdown north finder data acquisition technology

 With the development of inertial technology, strap-down north finder has become the main trend of development because of its speed, high reliability, no need to provide geographical location information and simple structure. North finder plays an important role in military applications such as missile launching and artillery aiming. In practical engineering applications, the operating latitude of the north finder is from 53° South to 53° north. In the range of Earth latitude 0° ~ 53°, the north component of the earth's rotation angular velocity varies greatly, and the amplitude of the gyroscope output signal will have a large difference. When the sampling resistance of the signal acquisition system is fixed, the gyro data fitting curves are different in different geographical latitudes, and some geographical latitude data fitting curves will lead to data loss, which will have a certain impact on north finding.

 

1.The overall design of strap-downnorth finding system

 

The strap-down north seeking system is composed of data acquisition and processing system, turntable leveling system (inclinometer), rotation control system (servo unit), inertial measurement system (fiber optic gyro and accelerometer), temperature control system (temperature control unit), etc. The data acquisition and processing system is composed of signal acquisition module, signal processing module, data display module and data communication module, which is the central processing core of the north finder, mainly realizing the function of data acquisition and processing and calculating the north seeking angle. The signal acquisition module converts the current signal output by the gyro into voltage signal, and then converts it into digital signal through A/D. The signal processing module performs digital filtering on the gyro data, processes the gyro data and encoder data of multiple transposition positions, and calculates the north seeking angle. The data display module displays the working state and north seeking angle data of the north finder; Data communication module communicates with servo control unit, temperature control unit, electronic inclinometer, encoder and host computer through serial port, and sends and receives data.

 

2.Fiber optic gyroscope data acquisition

 

The fiber optic gyro adopts differential pulse output mode. The output of each gyro consists of positive and negative pulses. The pulse frequency varies with the carrier's angular velocity. The range is 0~2MHZ and the pulse width is 250ns. How to ensure that the pulse is not lost is very important, so the design of high frequency and reliable pulse counting to count the output pulse of the gyroscope, in order to prevent the interference of the peak jitter pulse, the gyro pulse is firstly filtered and shaped in the front end of the pulse counter module, and then the level frequency doubling sampling is adopted, because the sampling triggered by the pulse rising edge or falling edge will produce false triggering, and the reliability is low.

 

The update frequency of IMU data in the north finder is 100 Hz, that is, the gyroscope data sampling period is 10ms. When the 10ms interrupt signal rises, the positive and negative counters will be subtraction to obtain the gyroscope data. The result will be temporarily stored in the register, and the counter will be cleared to zero to start the next count. The gyro data in the register is sent to the data RAM for DSP reading when the 10ms interrupt signal falls along the edge. In addition, in order to improve sampling accuracy of the system, oversampling technology is adopted during sampling, that is, a large number of gyro data are collected within each sampling period, and then used for azimuth solution after smoothing and filtering.

 

In order to verify the correctness and reliability of the design of the pulse counter, a signal generator is used to generate pulse signals, which are connected to the pulse acquisition port of the data acquisition unit, the number of pulses generated by the signal generator is collected in a fixed period of time, and sent to the computer through the serial port. The experimental results are shown in Table 1, where the pulse width is 80ns, the amplitude is 3.3V, and the sampling time is 10ms.

It can be seen from the measurement diagram that the number of pulses sent by the signal generator and the number of pulses collected 1 verify the correctness of the design of the pulse counter. The output of the accelerometer is converted into A pulse signal after A/D conversion, which is similar to the gyroscope data acquisition, and will not be repeated.

 

3.Serial port expansion

 

The IMU and attitude data need to be sent to the upper control microcomputer through the serial port. The DSP chip in this system has only one synchronous serial port, so it is necessary to design an asynchronous serial port. For the extension of DSP synchronous to asynchronous serial port, the traditional method is to use special asynchronous communication devices to achieve. Based on the abundant I/O resources of FPGA, this paper uses Verilog language to describe UART and realize the conversion of synchronous and asynchronous protocols, which not only simplifies the hardware circuit but also reduces the burden of DSP. At the same time, using FPGA to design the serial port can reduce the cost and volume of the system and has the advantages of easy transplantation and upgrading.

 

Conclusion

 

From the perspective of practical application, this paper introduces the system design in detail, aiming at the requirement of real-time, reliability and precision, multi-channel data acquisition unit of north seeker. Based on the data acquisition technology of north seeker, Ericco continues to improve its own technology, if you are interested, welcome to check our specific products, among which ER-FNS-03 solves the expensive characteristics of traditional FOG north finder with the advantage of low cost, ER-MNS-05 and ER-MNS-06 combine with MEMS technology, manufacture a small medium and high precision north finder, welcome to your understanding.

The full article can be seen: https://www.ericcointernational.com/application/analysis-of-strapdown-north-finder-data-acquisition-technology.html