Ground velocity sensor with drop-out detection

A radar or sonic velocity sensor for sensing the velocity of an object moving relative to the sensor, the velocity sensor comprising:

• first means for determining velocity data from a velocity dependent frequency derived from a variable magnitude signal reflected from the object and from a predetermined fixed frequency, the first means operating without mixing the variable magnitude signal with the fixed frequency;
• and
• second means for limiting the effect of reflected signal degradation upon derivation of the velocity data, the variable magnitude reflected signal being received by an input of the second means and the second means having an output coupled to an input of the first means;
• the second means comprising a drop-out detector for sensing fluctuations in the average magnitude of the reflected signal and for generating a drop-out signal only when the average magnitude is below a predetermined threshold, the drop-out detector comprising a rectifier for rectifying the reflected signal, an averaging circuit for generating an average signal representing an average amplitude of the rectified signal, and a comparator having a first input coupled to receive said threshold, a second input coupled to receive the average signal and an output which is coupled to the hold means;
• the first means comprising a phase-locked-loop circuit responsive to the velocity dependent frequency for generating an output signal which varies in response to changes in the velocity dependent frequency and thus, to changes in object velocity, the phase-locked-loop circuit including hold means responsive to the drop-out detector for preventing variations of the output signal when the drop-out detector is generating the first signal.

A radar or ultrasonic velocity sensor for sensing the velocity of an object moving relative to the sensor, the velocity sensor comprising:

• first means for determining velocity data from a velocity dependent frequency derived from a variable magnitude signal reflected from the object and from a predetermined fixed frequency;
• and
• second means for limiting the effect of reflected signal degradation upon derivation of the velocity data, the variable magnitude reflected signal being received by an input of the second means and the second means having an output coupled to an input of the first means;
• the second means comprising a drop-out detector for sensing fluctuations in the average magnitude of the reflected signal and for generating a drop-out signal only when the average magnitude is below a predetermined threshold;
• the first means comprising a phase-locked-loop circuit responsive to the velocity dependent frequency for generating an output signal which varies in response to changes in the velocity dependent frequency and thus, to changes in object velocity, the phase-locked-loop circuit including hold means responsive to the drop-out detector for preventing variations of the output signal when the drop-out detector is generating the first signal;
• the phase-locked-loop circuit comprising:
• a phase comparator with one input coupled to receive the velocity dependent frequency, an output and another input;
• a voltage controlled oscillator with an output coupled to the other input of the phase comparator and an input;
• a switch having a first terminal coupled to the output of the phase comparator, a second terminal, and a third terminal coupled to receive the drop-out signal, the switch being operable to connect and disconnect the first and second terminals as a function of the drop-out signal which is applied to its third terminal;
• an integrator having an input coupled to the second terminal of the switch and having an output;
• and
• a summing amplifier having a first input coupled to receive the output of the phase comparator, a second input coupled to receive the output of the integrating amplifier and an output coupled to the input of the voltage controlled oscillator.

A radar or sonic velocity sensor for sensing the velocity of an object moving relative to the sensor, the velocity sensor being of the type having a single transmitter for directing a transmit frequency signal towards the object and having a single receiver for receiving a variable magnitude unmixed signal reflected from the object, the velocity sensor comprising:

• first means for determining velocity data from a velocity dependent frequency derived from the variable magnitude signal reflected from the object and from a predetermined fixed frequency signal, the first means operating without mixing the variable magnitude signal with the fixed frequency signal;
• and
• second means for limiting the effect of reflected signal degradation upon derivation of the velocity data, the variable magnitude refected signal being received by an input of the second means and the second means having an output coupled to an input of the first means;
• the velocity sensor further comprising:
• a first circuit responsive to the fixed frequency signal for generating a first signal proportional to the fixed frequency signal;
• a drop-out detector for sensing fluctuations in the average magnitude of the reflected signal and for generating a drop-out signal only when the sensed magnitude is below a predetermined threshold;
• a second circuit responsive to the velocity dependent frequency for generating a second signal which varies in response to changes in the velocity dependent frequency, the second circuit including a hold circuit for preventing variation of the second signal in response to generation of the drop-out signal;
• and
• a third circuit for generating an output signal with a magnitude which is proportional to the object velocity and which is a function of the first and second signals.

A radar or sonic velocity sensor for sensing the velocity of an object moving relative to the sensor, the velocity sensor comprising:

• first means for determining velocity data from a velocity dependent frequency derived from a variable magnitude signal reflected from the object and from a predetermined fixed frequency, the first means operating without mixing the variable magnitude signal with the fixed frequency;
• and
• second means for limiting the effect of reflected signal degradation upon derivation of the velocity data, the variable magnitude reflected signal being received by an input of the second means and the second means having an output coupled to an input of the first means;
• the first means comprising first and second counters, the first counter receiving the velocity dependent frequency and establishing a variable length time period corresponding to a predetermined number of cycles of the velocity dependent frequency, the second counter receiving the fixed frequency and counting at said fixed frequency for said established time period, the contents of said second counter at the end of said time period being indicative of the object velocity;
• and the second means comprising a drop-out circuit for inhibiting the first and second counters when a magnitude of the reflected signal drops below a predetermined threshold.

A radar or sonic velocity sensor for sensing the velocity of an object moving relative to the sensor, the velocity sensor comprising:

• first means for determining velocity data from a velocity dependent frequency derived from a variable magnitude signal reflected from the object and from a predetermined fixed frequency, the first means operating without mixing the variable magnitude signal with the fixed frequency;
• and
• second means for limiting the effect of reflected signal degradation upon derivation of the velocity data, the variable magnitude reflected signal being received by an input of the second means and the second means having an output coupled to an input of the first means;
• the first means comprising period measuring means for measuring the period of a predetermined number of cycles of said velocity dependent frequency, the period measuring means comprising a first counter counting said predetermined number of cycles at a rate equal to the velocity dependent frequency, and a second counter counting at a constant rate for said period;
• and
• the second means including means for preventing the measured period from being influenced when the reflected signal has a magnitude which falls below a threshold.