Measuring Angular Displacement
Angular displacement is movement around an axis, such as the angular motion of the shaft of a motor. An angular displacement sensor is a device whose output signal represents the rotation of the shaft; it cannot measure the physical displacement of the whole shaft. One type of sensor used to measure angular displacement is a rotary variable differential transformer (RVDT). Another type of sensor used to measure angular displacement is a resolver, which is a rotating transformer that can measure 360° of rotation.
On M Series devices, C Series devices, and NI-TIO-based devices, you can use the counters to perform displacement measurements with quadrature encoders, or angular encoders. You can measure angular position with X1, X2, and X4 angular encoders. You can choose to do either a single-point or a buffered sample clock displacement measurement.
You also can measure velocity with angular encoders, but you need to use a sample clock with a fixed frequency. To measure velocity, use the following formula:
V = D/T
where V is the average velocity, D is the distance, and T is time.
The counter measures the position of the encoder using the A and B signals, which are offset by 90°. The counter also supports the Z index, which provides a precise reference point and is available on some encoders.
Creating a Program