JPS6488145A - Humidity measuring instrument - Google Patents

Abstract

PURPOSE:To accurately measure the humidity of the periphery of a developing device by providing a temperature measuring circuit which has a temperature sensor and finding relative or absolute humidity or a mixing ratio by a controller according to its measurement information and the information of a humidity sensor. CONSTITUTION:The secondary output of a transformer T1 is supplied to the controller 18 through a rectifier D1 and a stabilizing circuit Q1 and also supplied to a humidity measuring circuit 21 through a rectifier D2, so that it is connected to a temperature and humidity sensor 19. The circuit 21 applies a bias by a power circuit 37, the output of a temperature sensor 19b is put within a specific voltage range by an operational amplifier 32, and the output of a terminal P3 is supplied to the A/D converter of the controller 18. A humidity sensor 19a is supplied with an oscillation output whose amplitude and frequency are constant through the circuit 31, and the output is rectified by a detecting circuit 34 through a capacitor C2, smoothed by an integrating circuit 35, and inputted to the A/D converter of the controller 18 through an operational amplifier 36. The controller controls a primary high voltage power source 4a, a grid bias 4b, and a developing bias power source 1a to accurately measure variation at the periphery of a developing device 1, thereby compensating variation in development characteristics.