JPS6421325A - Displacement detector for balance - Google Patents

Abstract

PURPOSE:To achieve a higher detection sensitivity, by increasing the quantity of light incident into one of two photodetectors when a balance scale is displaced while the quantity of light incident on the other detector decreases to determine a output difference between the two photodetectors. CONSTITUTION:First and second shutters 17 and 18 increase or decrease the quantity of light incident into a first photodetector 23 separately by causing animbalance in balance scales 2 and 4 while decreasing or increasing the quantity of light incident on a second photodetector 24 reversely. With such an arrangement, it is assumed that the quantity of light incident on the first photodetector 23 increases by DELTAI with the displacement of the first shutter 17. The quantity of light incident on the first photodetector 23 further increases by DELTAI with the displacement of the second shutter 18, eventually by 2DELTAI. On the other hand, the quantity of light incident on the second photodetector 24 decreases by 2DELTAI reversely. Thus, difference between outputs of the photodetectors 23 and 24 gives 4DELTAI thereby achieving a higher detection sensitivity.