Operation of a computer-controlled equi-inclination X-ray diffractometer

The control program for a Buerger–Supper equi-inclination diffractometer on-line to a PDP-8/S computer is described. The computer calculates the angular settings, scan-range and optimum scan-speed for each reflexion, pulses stepping motors to provide the crystal and counter motions, inserts attenuators or balanced filters, and activates and interrogates the scaler which is part of the standard counting circuitry. A careful choice of counter apertures, and the re-measurement of reflexions whose precision or background imbalance fails to meet pre-set criteria, appear to overcome the major systematic errors to which diffractometer data recorded in the equi-inclination ω-scan mode are subject.