The displacer rod, made from a stainless steel pipe, is guided by two brass bushings placed inside the displacer rod guide house. Leakage through these bushings is prevented by two rubber seals. Both ends of the power-piston and displacer connecting rod which are made from steel, are fitted with two ball bearings. Details of the testing facilities are shown in Fig. 2. The intensity placed on the absorber plate (or displacer head) is measured by a pyranometer (Lambert model 00.16103.000000 CM3, calibrated constant
of which is 23.66 lV/Wm2). The sensitivity of the intensity measurement obtained from the pyranometer is ±0.05%.