Position sensor key terms

Incremental sensors

Only the bearing change information is provided so that the practice bearing is unknown at startup. Each time the index/symbol signal is used to say the zero or zero bit of the device. Detected in the homing procedure. For commutation of brushless motors, the motor typically has three magnetic Hall sensors that provide rough positive orientation information for the start of the magnetic field. Incremental sensors are typically small, accurate, and cost-effective.

Absolute sensors

Provides a practical physical orientation within one revolution or on the scale of a linear stroke. The motor does not need Hall, as long as the scale of movement exceeds one revolution, it needs to be used for rotation homing. Sensors are typically larger and more valuable than incremental devices.

Multi-turn

Rotating equipment, sensors can provide multi-rotation practice orientation. It is possible to completely eliminate homing. Multi-reverse equipment with internal gear equipment is the largest and most valuable solution.

Position sensor key terms

resolution

The boundary is the smallest azimuth increment that can be moved or measured, usually expressed as a "count". High-performance servo systems require high resolution. The positioning system "flutters" between the two counts, so the higher the resolution, the less flutter. Resolution also has a significant impact on speed fluctuations at low speeds. Since velocity is derived from the azimuth reaction, the data in the sample may not be sufficient to accurately determine the velocity if the resolution is low. At high speeds, high-resolution devices are capable of generating data rates that exceed the ability of controllers or servo drives to track.

interpolation

It can be seen that many sensors have sine and cosine signals. The period of these signals is determined by the "pitch" inherent to the device. Using the sin/cos information, it is theoretically possible to calculate the signal ratio to obtain infinite resolution. This skill is called interpolation. In practice, the fidelity and signal-to-noise ratio of the sin/cos signal limit the achievable resolution.

accuracy

The boundary says the interval between each measured bearing and the physical orientation being practiced. Accuracy is largely a system problem and can be affected by mechanical errors such as eccentricity, straightness and flatness. Sensor errors include non-cumulative random changes in fundamental tones (linearity), accumulation of fundamental errors (slope), and changes in the fidelity of internal sin/cos signals. Precision machine builders often calibrate for errors with offset lookup tables.

repeatability

The world says that when the system repeatedly returns to the same physical orientation, the scale of the measurement of the orientation. Repeatability is more important than affirmation of accuracy. In order to effectively calibrate for system errors, it is important to keep each azimuth reading consistent. Sensor hysteresis (different readings depending on the approach direction of the measured bearing) is an important factor in repeatability.

modularization

The most common form of rotational reaction equipment is encapsulated in a housing with internal bearings and a shaft connected to a motor by a flexible coupling. Enclosures are available in a range of sealing levels, and bulky modular devices have no housings or bearings, and need to be built into the mechanical system. They are significantly more compact, but perhaps require a friendlier environment, depending on skills.

On/off shaft

For rotary use, the sensor is typically located off-axis on the circumference of the scale around the axis of rotation. When the radial space is constrained, some finishes position the sensor on the size of the axis minimization.

potentiometer

Despite the trend towards non-touch sensors, potentiometers ("potentiometers") are still widely used in low-end applications. A potentiometer measures the voltage drop when a contact slides along a resistive track. They are available in rotary, linear or curvilinear form and are usually compact and simple. A simple device will cost a few cents, while a more precise device may cost more than $200. The resistance trajectory is laser-trimmed to achieve a linearity of less than 0.01%.

Potentiometers are best used in low-function use with a low duty cycle in a benign environment. They are susceptible to abrasion and foreign objects such as dust or sand particles. Potentiometers theoretically have infinite resolution, but in practice the resolution is limited to the analog-to-digital converter (ADC) interface and the entire noise environment.

Advantages: low cost; Briefly; Compact; Simple. Be precise

Weaknesses: Wear and tear; Vibration; Pollution, extreme temperatures.

Position sensor key terms

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