GT-1A aviation gravimeter gravity sensor is shown in Figure 4-4-2. The heavy load is connected to the base with two 50?m wide springs. Under the action of magnetic fields in two opposite directions , the heavy load is in a suspended state.
In the factory, a stable current I is set to generate a balancing force supporting a 37 g load through the compensation coil, so that the load is at the zero position (rest point). Due to the influence of factors such as drift, static measurements need to be performed at fixed reference points before and after flight measurement for drift correction.
The calculation formula of stable current I is:
Figure 4-4-2 GT-1A gravity sensor (GSE) working principle diagram
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In the formula: I is the stable current; m is the heavy load mass; g0 is the gravity constant; k is a constant (depends on the compensation coil).
When the gravity field acting on the heavy load changes, the LED and photosensitive sensor provide an electrical signal proportional to the offset of the heavy load. This signal is converted into a current and added to the measuring coil, so that The weight returns to the zero position (resting point). In this way, a current proportional to the vertical apparent acceleration Wz flows through the measurement coil of the gravity sensor (the first coil) and the reference resistor in series with the coil. The voltage signal generated on the reference resistor is input to the microprocessor through the ADC. , and converted into vertical gravity value Wz.
Another reference current generated by the microprocessor to balance gravity is loaded on the second coil (compensation coil) of the gravity sensor force sensor, and the magnetic force generated by the energized coil is used to adjust the offset heavy load. Return it to the zero position.
This measurement is still analog control, with a response speed of approximately 100 Hz. Constant temperature is crucial for gravity sensors.
Compensation factors for sensor deflection due to vibration are obtained through vibration testing in the factory. Different vibration frequencies were set for testing, ranging from a few Hz to nearly 100 Hz.
Figure 4-4-3 shows the vibration test results of gravity sensors at different frequencies, with vibration frequencies ranging from 5 to 70 Hz. Through vibration tests at different frequencies, the offsets of the gravity sensor at different frequencies are obtained. The blue line in the figure represents the readings of the gravity sensor at different vibration frequencies. It can be seen from the figure that when the vibration frequency is 60 Hz, the gravity sensor reading deviation due to vibration is close to 100×10-5m·s-2. The red line in the figure represents the load position offset measured at different vibration frequencies (unit: m2). The compensation coefficient is obtained by the following formula:
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The green line in the figure is the measurement result obtained after correction using the compensation coefficient, and the influence of vibration is reduced. 20 times.