Determining the gravitational constant with the gravitation torsion balance after Cavendish
- Recording the excursion and evaluating the measurement with the IR position detector and PC

The IR position detector (IRPD) enables automatic measurement of the motion of the lead balls in the gravitation torsion balance. The four IR diodes of the IRPD emit an infrared beam; the concave mirror on the torsion pendulum of the balance reflects this beam onto a row of 32 adjacent phototransistors. A microcontroller switches the four IR diodes on in sequence and then determines which phototransistor is illuminated each time. The primary S range of illumination is determined from the individual measurements.
The IRPD is supplied complete with the demo version of CASSY Lab, for direct measurement and evaluation of the experiment P1.1.3.2 using a computer with Windows XP or higher. The system offers a choice of either the end-deflection or the acceleration method for measuring and evaluating.