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Abstract

The oscillation of an oscillator is automatically stopped during gas sampling, and the gas sampling is automatically stopped during the measurement of the frequency of the oscillator before and after the gas sampling, thereby making it possible to avoid the measurement error due to a change in resonance frequency by the effect of dynamic and static pressures applied to a filter paper holder mounted at the free end of the oscillator in the gas sampling, and to prevent the dislodgement and reentrainment of suspended particulates collected in the filter paper due to the oscillation acceleration. Accordingly, it is possible to accurately measure the mass of suspended particulates deposited on a filter paper compared with the conventional method in which the gas sampling and the measurement of the frequency are simultaneously and continuously performed while oscillating an oscillator. Concretely, a gas switching valve is provided between an oscillator and a pump, and a signal switch is provided between a sensor and an automatic gain control amplifier. With this construction, the oscillation of the oscillator is stopped during the gas sampling, and the gas sampling is stopped during the measurement of the frequency of the oscillator before and after the gas sampling on the basis of a synchronous control signal from a control processor.

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