CONCENTRATION MEASURING APPARATUS WITH ZERO-POINT CALIBRATION

摘要

PURPOSE:To always detect the concentration of powder accurately without frequenty manual zero-point calibration by performing the zero-point compensation based on the average concentration of the powder obtained when the start of pneumatic conveyance thereof is detected depending on variation range in the average concentration thereof. CONSTITUTION:Signals which are changing sharply generating at the start of pneumatic conveyance of powder are processed with a coupling condenser C, a rectifier 14 and the like separately from those corresponding to the concentration of the powder pneumatically conveyed through a conduit 2 through an electrostatic capacitance detection circuit 6 and a signal sampling circuit 17 is controlled according to the results as variation range in the concentration thereof. The average concentration of the powder from a d.c. amplifier 11 including LPE during the detection of the start of the pneumatic conveyance thereof is sampled and stored in a memory 19 to constitute a drift value due to powder or the like attached to the wall of a tube 2. This enables the zero- point calibration to be performed automatically through a differential amplifier 21 each time the concentration of the powder is detected. Thus, the detection of the concentration of the powder can be always performed accurately without any frequent manual zero-point calibration.