Propagation time measurement machine, gas concentration measurement device, propagation time measurement program, and propagation time measurement method

A propagation time measurement program to be read by a propagation time measurement machine including;

• a reception unit that receives ultrasonic waves;
• and a computation unit that obtains a time required for the ultrasonic waves to propagate in a predetermined measurement space, based on a first reception signal output from the reception unit based on first ultrasonic waves received by the reception unit, and a second reception signal output subsequent to the first ultrasonic waves from the reception unit based on second ultrasonic waves received by the reception unit, the propagation time measurement program causing the computation unit to execute processing of:
• correlation object determination processing for obtaining a first correlation object signal obtained based on a first upper-limit rate of change, which is a rate of change of an upper-limit envelope of the first reception signal, and a first lower-limit rate of change, which is a rate of change of a lower-limit envelope of the first reception signal, and a second correlation object signal obtained based on a second upper-limit rate of change, which is a rate of change of an upper-limit envelope of the second reception signal, and a second lower-limit rate of change, which is a rate of change of a lower-limit envelope of the second reception signal;
• correlation processing for obtaining a correlation value between the first correlation object signal and a signal obtained by moving the second correlation object signal on a time axis;
• and
• propagation time measurement processing for obtaining a time difference between the first correlation object signal and the second correlation object signal based on the correlation value, and obtaining the time required for the ultrasonic waves to propagate in the measurement space, based on the time difference.

A propagation time measurement method to be executed by a propagation time measurement machine including;

• a reception unit that receives ultrasonic waves;
• and a computation unit that obtains a time required for the ultrasonic waves to propagate in a predetermined measurement space, based on a first reception signal output from the reception unit based on first ultrasonic waves received by the reception unit, and a second reception signal output subsequent to the first ultrasonic waves from the reception unit based on second ultrasonic waves received by the reception unit, the propagation time measurement method causing the computation unit to execute processing of:
• correlation object determination processing for obtaining a first correlation object signal obtained based on a first upper-limit rate of change, which is a rate of change of an upper-limit envelope of the first reception signal, and a first lower-limit rate of change, which is a rate of change of a lower-limit envelope of the first reception signal, and a second correlation object signal obtained based on a second upper-limit rate of change, which is a rate of change of an upper-limit envelope of the second reception signal, and a second lower-limit rate of change, which is a rate of change of a lower-limit envelope of the second reception signal;
• correlation processing for obtaining a correlation value between the first correlation object signal and a signal obtained by moving the second correlation object signal on a time axis;
• and
• propagation time measurement processing for obtaining a time difference between the first correlation object signal and the second correlation object signal based on the correlation value, and obtaining the time required for the ultrasonic waves to propagate in the measurement space, based on the time difference.