| 摘要 |
PURPOSE:To measure a frequency change even with a counter having a small number of bits by subtracting new measured value from preceding new measured value by (n) and dividing the cumulative difference by (n). CONSTITUTION:A sensor 1 which sucks smells, etc., and the resonance frequency of which changes is set in a gas to be measured and resonates when an oscillation circuit 2 is driven. A counter 11 inputs the resonance frequency signal of the sensor 1 and measures the frequency of the signal. A storage circuit 13 and subtracting circuit 14 input the measured value of the counter 11. The circuit 13 stores past (n) measured values and, when a new measured value is inputted, outputs the oldest value among the storing measured values, namely, the measured value preceding the new measured value by (n) measured values to the circuit 14. The circuit 14 subtracts the oldest measured value from the new measured value and outputs the difference to an adding circuit 15 and the circuit 15 adds the output signal of the circuit 14 to a cumulative value stored in a storage circuit 16 and stores the new cumulative value in the circuit 16. Then a dividing circuit 8 divides the output signal of the circuit 16 by (n) and a frequency converting circuit 9 converts the output of the circuit 8 into a frequency value from the count value and outputs a signal 100a. |
