Servo System for Automatic Dose Control

Circuitry has been designed and constructed such that conveyor motion past a scanned Linear Accelerator beam is automatically regulated as a function of average beam current. Using this, the ratio of average current to conveyor speed can be held constant, thereby eliminating beam current variation as a source of error in irradiation processing. In the system, the ratio of current to conveyor speed is computed, multiplied by a factor inversely proportional to the scan height, and displayed on a digital voltmeter. The current signal is derived from a secondary emission monitor within the accelerator, while the conveyor speed is sensed by a tachometer coupled with the conveyor drive assembly. The beam scan is detected by a pair of adjustable sensor bars which are perpendicular to the plane of scan.