Servo Concepts
RCP8 provides two independent, nearly identical motion servos for the radar antenna azimuth and elevation axes. The servos are implemented digitally in the RCP8 microprocessor.
The servo software takes as input the digital antenna position and analog tachometer velocity and provides, as output, an analog drive signal for the motor power amplifiers. The interface between the processor and the tachometer and drive signals is made using 12-bit A/D and D/A converters.
The servo software is periodically scheduled at 10 millisecond intervals and, in principal, can control antennas that have a significant response, such as 20 Hz. In practice, most weather radar antennas are much slower. Except for the limit switches in the elevation axis, the servos are identical in configuration and operation.
| Option | Description |
|---|---|
| Open loop |
The open loop is not really a servo. It applies fixed drive levels to the motor to measure the antenna performance. The open loop only runs during installation to measure the antenna's characteristics to set up the actual control parameters. This a manual procedure requires the local TTY. See TTY MONITOR Command. |
| Velocity servo |
The velocity and the position servos are related - each mechanism uses parts of the other during normal operation. The velocity servo always runs when either servo is activated. To achieve a particular velocity, the servo is used directly. To achieve a particular position, a non-linear position error is fed into the velocity servo from the position servo. |
| Position servo |
The position servo is implemented in the following stages:
Theoretically, this 2-stage position servo can always be made stable - the position can always be reached without overshoot or oscillation. The non-linear feedback function can also be tailored to achieve stability and high performance. This means that a requested position is reached in the shortest possible time. |