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An accurate air temperature measurement system based on an envelope pulsed ultrasonic time-of-flight technique
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Image of FIG. 1.
FIG. 1.

The emission and the echo waveform from a pair of ultrasonic transducers. Accurate TOF is hard to predict because inertia delay is included and the measured TOF is dependent on the echo waveform’s detection threshold level.

Image of FIG. 2.
FIG. 2.

The proposed APESW wave has three components. First it transmits ten low-amplitude pulses. Second, it transmits two high-amplitude pulses. Lastly, the APESW transmits another ten low-amplitude pulses. Pulse train 2, which is the measurement pulse and the following ten low-amplitude pulses, has a phase difference of when compared to pulse train 1.

Image of FIG. 3.
FIG. 3.

The APESW signal generation, transmission, and processing system block diagram.

Image of FIG. 4.
FIG. 4.

APESW waves are supplied to an ultrasonic transmitter. The corresponding receiver generates echo waves . Echo waves are transformed from an analog signal to received digital signal . Two phase modulation detectors (PM detectors 1 and 2) are used to sense the transmitted measurement pulse and the received relative pulse. The measurement of TOF is derived from the time difference between the outputs of PM detectors 1 and 2.

Image of FIG. 5.
FIG. 5.

The TOF calculation is the sum of the counter clock integer and the last incomplete cycle’s phase shift quantity. The transmitted signal is aligned with the counter clock’s rising edge.

Image of FIG. 6.
FIG. 6.

The phase shift quantity is counted by the original system clock . The counter clock is activated when the system senses the phase inversion of the received signal (the rising edge of PM detector 2). The counter clock is deactivated once the next falling edge of the counter clock is detected. The phase shift quantity between the transmitted and received signals can be obtained by calculating the phase quantity from the equation .

Image of FIG. 7.
FIG. 7.

The effect of humidity on sound velocity ratio for six temperature values.

Image of FIG. 8.
FIG. 8.

The system’s hardware circuit, including the driving circuit for the ultrasonic transmitter and the amplifier circuit for the ultrasonic receiver.

Image of FIG. 9.
FIG. 9.

The amplitude modulation (AM) is achieved by modulating the supplied power for the output amplifier CD4069. After amplitude modulation, the APESW has two signal levels, and . Additionally, the phase modulation can be achieved by controlling the pulse width of the transmitted signal from the CPLD (PM signal).

Image of FIG. 10.
FIG. 10.

The CPLD programed circuit block diagram.

Image of FIG. 11.
FIG. 11.

The system’s software block diagram.

Image of FIG. 12.
FIG. 12.

The block diagram of the experiment system.

Image of FIG. 13.
FIG. 13.

(a) The actual temperature vs the derived temperature measurements from TOF at . (b) The plot of temperature deviations vs actual temperature. (c) Humidity effect on fixed temperature measurements. (d) Measured distance effect on fixed temperature measurements.


Generic image for table
Table I.

Experimental conditions of three separate experiments.

Generic image for table
Table II.

Experimental uncertainty budget.


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Scitation: An accurate air temperature measurement system based on an envelope pulsed ultrasonic time-of-flight technique