I. Angle Sensor and its Installation
An angle sensor, as the name suggests, is used to detect angles. It has a hole in its body that allows it to engage with a LEGO axle. When connected to an RCX, the angle sensor counts once for every 1/16th of a revolution of the axle. The count increases when rotating in one direction and decreases when the direction of rotation changes. The count is related to the initial position of the angle sensor. When the angle sensor is initialized, its count is set to 0; you can reset it programmatically if needed.
Wiring method and principle of angle displacement sensor: The three terminals or three wires (red, yellow, and blue) are labeled 1, 2, and 3, respectively, indicating: 1 is the input terminal; 2 is the output terminal; and 3 is ground. (Note: If the wire at terminal 2 is connected incorrectly, the sensor will be burned out.) When the shaft rotates or moves linearly from terminal 1 to terminal 3, the resistance changes. The resistance is output with high precision from terminal 2 according to a linear law. At the same time, the resistance change is converted into a signal display through a conversion circuit.
The installation steps for the angle sensor are as follows:
1. Position the sensor using the mounting boss and secure it to the metal plate with screws, nuts, or clamping plates. During sensor installation, do not machine or drill the shaft or housing. Avoid subjecting the shaft or housing to external impacts or pressures. The axial and radial directions of the shaft must not be subjected to impacts or pressures (static pressure should be less than 300N). Do not loosen the screws on the sensor or rotate the retaining ring.
2. When connecting the sensor output shaft to other components, ensure that the shaft centerline is in a straight line (including during operation). If there is any deviation in the shaft centerline, it is recommended to use universal joints or bellows or other adapters to prevent the sensor output shaft from bending or deforming, which could damage other components and affect its use.
3. Prevent water droplets, vapor, solvents and corrosive gases from attacking the sensor, and prevent metal shavings or other powders from entering the sensor.
4. The external wiring of the sensor should be soldered to the groove at the lead-out end, and should not be soldered to the top of the lead-out end as much as possible. When soldering, a soldering iron with a power of no more than 45W should be used, and the soldering time should be less than 5 seconds. Do not pull the wire while soldering or before it has cooled completely, so as to prevent the brush filament or the entire lead-out end from being pulled out or even falling off.
II. How to Select an Angle Sensor
1. Sensitivity Selection
Generally, within the linear range of an angle sensor, higher sensitivity is desirable. This is because higher sensitivity results in a larger output signal corresponding to changes in the measured quantity, which is beneficial for signal processing. However, it's important to note that high sensor sensitivity also makes it easier for external noise unrelated to the measured quantity to enter the sensor and be amplified by the amplification system, affecting measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio to minimize interference signals introduced from the outside.
Sensor sensitivity is directional. When the measured quantity is a single vector and its directionality is critical, a sensor with low sensitivity in other directions should be selected; if the measured quantity is a multi-dimensional vector, the lower the cross-sensitivity of the sensor, the better.
2. Frequency response characteristics
The frequency response characteristics of an angle sensor determine the frequency range of the measurement. It is necessary to maintain distortion-free measurement conditions within the allowable frequency range. In reality, the sensor response always has a certain delay, and it is desirable to minimize the delay time.
A sensor with a high frequency response can measure a wide range of signal frequencies. However, due to the influence of structural characteristics, mechanical systems have greater inertia, resulting in sensors with low frequencies being able to measure signals with lower frequencies.
Selection of Angle Sensor
In dynamic measurements, the response characteristics of the signal (steady-state, transient, random, etc.) should be considered to avoid excessive errors.
3. Linear range
The linear range of an angle sensor refers to the range within which the output is proportional to the input. Theoretically, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger its measurement range and the better it guarantees a certain level of measurement accuracy. When selecting a pressure sensor, once the type of sensor is determined, the first thing to check is whether its measurement range meets the requirements.
However, in reality, no sensor can guarantee perfect linearity; its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, a sensor with small nonlinear errors can be approximated as linear, which greatly simplifies the measurement process.
4. Stability
The ability of a sensor to maintain its performance unchanged after a period of use is called stability. Besides the sensor's own structure, the main factor affecting the long-term stability of a sensor is its operating environment. Therefore, for a sensor to have good stability, it must have strong environmental adaptability.
In addition, before selecting an angle sensor, its operating environment should be investigated, and a suitable sensor should be selected based on the specific operating environment, or appropriate measures should be taken to reduce the impact of the environment.
