A transport apparatus includes a speaker and a mike disposed at respective positions between which a transport path of a medium is interposed, where the speaker and the mike face each other, a drive circuit that outputs a drive signal to the speaker, an amplifier circuit formed by coupling a plurality of amplifiers in series, where the amplifier circuit amplifies and outputs an output signal of the mike, a processor to which the output signal of the amplifier circuit is input, an attenuation circuit disposed in a stage preceding a predetermined amplifier, where the attenuation circuit attenuates an input signal and outputs the input signal to the predetermined amplifier, and a switch that switches an attenuation factor by the attenuation circuit.

An image processing apparatus includes a transmitter, a receiver, a comparison circuit, and a control unit. The transmitter transmits an ultrasonic wave to a conveyance path through which a sheet is conveyed. The receiver faces the transmitter with the conveyance path in between, and receives the ultrasonic wave transmitted by the transmitter. The comparison circuit compares a level signal indicating a reception level of the ultrasonic wave received by the receiver with a threshold signal for determining whether or not the sheet is double-fed in the conveyance path, and outputs a comparison result signal according to the comparison result. The control unit determines whether or not there is a possibility of a defect in the double feed detection function of detecting double feed based on the comparison result signal and the level signal.

An image processing apparatus includes a transmitter, a receiver, a comparison circuit, and a control unit. The transmitter transmits an ultrasonic wave to a conveyance path through which a sheet is conveyed. The receiver faces the transmitter with the conveyance path in between, and receives the ultrasonic wave transmitted by the transmitter. The comparison circuit compares a level signal indicating a reception level of the ultrasonic wave received by the receiver with a threshold signal for determining whether or not the sheet is double-fed in the conveyance path, and outputs a comparison result signal according to the comparison result. The control unit determines whether or not there is a possibility of a defect in the double feed detection function of detecting double feed based on the comparison result signal and the level signal.

A conveyor conveys a sheet along a conveyance path provided with an ultrasonic sensor, and includes: an updating member that successively updates a parameter indicating aged deterioration of the conveyor; a searcher that searches a look-up table storing pieces of noise data of noises predicted to be superimposed on a detection signal of the ultrasonic sensor in accordance with a degree of the aged deterioration, and obtains a piece of noise data corresponding to a current parameter value of the conveyor; and a signal processor that uses, for signal processing, a remaining portion of the detection signal of the ultrasonic sensor excluding a portion corresponding to the piece of noise data obtained by the searcher.

A transport apparatus includes a speaker and a mike disposed at respective positions between which a transport path of a medium is interposed, where the speaker and the mike face each other, a drive circuit that outputs a drive signal to the speaker, an amplifier circuit formed by coupling a plurality of amplifiers in series, where the amplifier circuit amplifies and outputs an output signal of the mike, a processor to which the output signal of the amplifier circuit is input, an attenuation circuit disposed in a stage preceding a predetermined amplifier, where the attenuation circuit attenuates an input signal and outputs the input signal to the predetermined amplifier, and a switch that switches an attenuation factor by the attenuation circuit.

A medium thickness detection device includes: a light emitting element; a constant-current control circuit controlling, in a constant-current manner, the light emitting element to output light passing through a medium for an irradiation time; a light-receiving element receiving the light passing through the medium to obtain an analog signal; a receiver circuit receiving the analog signal; a maximum holding circuit holding a maximum of the analog signal; an analog-to-digital converter circuit reading the maximum of the analog signal and converting the maximum of the analog signal into a digital signal; a reset circuit resetting the maximum holding circuit; and a processor controlling operations of the constant-current control circuit, the reset circuit and the analog-to-digital converter circuit, and determining a thickness of the medium according to the digital signal when a specification of the medium is unknown.

A paper warping detection device includes an input tray, a processor, a first emitting element, a first receiving element and a first analog-to-digital converter. A first critical value is stored in the processor. The first emitting element is electrically connected with the processor. The first receiving element is disposed to the other side of the input tray. The first receiving element and the first emitting element face each other. When the first emitting element is switched on, the first emitting element emits first ultrasonic wave signals towards the first receiving element. The first analog-to-digital converter is electrically connected with the first receiving element and the processor for converting the first ultrasonic wave signals into first digital signals and outputting the first digital signals to the processor. The processor reads the first digital signals and compares the first digital signals with the first critical value.

A paper warping detection device includes an input tray, a processor, a first emitting element, a first receiving element and a first analog-to-digital converter. A first critical value is stored in the processor. The first emitting element is electrically connected with the processor. The first receiving element is disposed to the other side of the input tray. The first receiving element and the first emitting element face each other. When the first emitting element is switched on, the first emitting element emits first ultrasonic wave signals towards the first receiving element. The first analog-to-digital converter is electrically connected with the first receiving element and the processor for converting the first ultrasonic wave signals into first digital signals and outputting the first digital signals to the processor. The processor reads the first digital signals and compares the first digital signals with the first critical value.