The present invention relates to time-of-flight ranging or pulse-echo ranging systems, and more particularly to a method and apparatus for calibrating operation of the pulse-echo ranging system for level measurement applications.
Pulse-echo acoustic ranging systems, also known as time-of-flight ranging systems, are commonly used in level measurement applications. Pulse-echo acoustic ranging systems determine the distance to a reflector (i.e. reflective surface) by measuring how long after transmission of a burst of energy pulses the echo or reflected pulses are received. Such systems typically use ultrasonic pulses or pulse radar signals.
Pulse-echo acoustic ranging systems generally include a transducer and a signal processor. The transducer serves the dual role of transmitting and receiving the energy pulses. The signal processor is for detecting and calculating the distance or range of the object based on the transmit times of the transmitted and reflected energy pulses.
Since the transmitted energy pulses are converted into distance measurements, any timing errors arising in the circuitry of the device result in distance measurement errors which degrade the accuracy of the level measurements. In most cases, timing errors are a result of temperature drift and drift over time in the operating characteristics of the electronics in the device circuitry. Accordingly, it is necessary to calibrate time-of-flight ranging systems not only at installation, but on a periodic basis as well in order to insure accurate level measurements.
While there is a need to periodically calibrate, the time-of-flight ranging systems are not always easily accessible after installation. In addition, there is a cost involved with a technician conducting calibration tests on an ongoing basis.
Accordingly, there remains a need to provide a system and techniques which facilitate calibration of pulse-echo or time-of-flight ranging systems while overcoming these and other perceived shortcomings.
The present invention provides a calibration module and calibration techniques for a pulse-echo acoustic ranging or time-of-flight ranging systems.
In a first aspect, the present invention provides a time-of-flight ranging system comprising: (a) a transducer for emitting energy pulses and detecting reflected energy pulses; (b) a controller; (c) a transmitter operatively coupled to the controller, and the transducer having an input port coupled to the transmitter module and being responsive to a transmit pulse signal for emitting the energy pulses; (d) a receiver operatively coupled to the controller, and the transducer including an output coupled to the receiver for outputting a reflected pulse signal corresponding to a reflected energy pulse coupled by the transducer; (e) the receiver converting the reflected pulse signal for input by the controller and the controller including a component for determining time-of-flight measurements from the reflected pulse signal; (f) a calibration module having a loop-back component for bypassing the transducer and routing the transmit pulse signal to the receiver, and the controller including a calibration component for processing the output from the receiver.
In another aspect, the present invention provides a method for calibrating a time-of-flight ranging system, the time-of-flight ranging system includes a transducer for emitting energy pulses and detecting reflected energy pulses, a transmitter operatively coupled to a controller and the transducer being responsive to a transmit pulse signal for emitting the energy pulses, a receiver operatively coupled to the controller and having an input for receiving a reflected pulse signal corresponding to a reflected energy pulse from the transducer, the receiver converting the reflected pulse signal for input by the controller and the controller including a component for determining time-of-flight measurements associated with the reflected pulse signal, the calibration method comprises the steps of: (a) bypassing the transducer and looping back the transmit pulse signal to the receiver; (b) inputting an output signal generated by the receiver corresponding to the looped-back transmit pulse signal; (c) measuring characteristics associated with the output signal; (d) determining calibration parameters from the measured characteristics.
In a further aspect, the present provides a time-of-flight ranging system comprising: (a) emitter means for emitting energy pulses and detecting reflected energy pulses; (b) controller means; (c) transmitter means for transmitting a transmit pulse signal, the transmitter means being operatively coupled to the controller, and the emitter means having an input port coupled to the transmitter means and the emitter means being responsive to a transmit pulse signal for emitting the energy pulses; (d) receiver means for receiving a reflected pulse signal, the receiver means being operatively coupled to the controller means, and the emitter means including output means coupled to the receiver for outputting the reflected pulse signal corresponding to a reflected energy pulse coupled by the emitter means; (e) the receiver means including means for converting the reflected pulse signal for input by the controller means and the controller means including means for determining time-of-flight measurements from the reflected pulse signal; (f) means for bypassing the emitter means and routing the transmit pulse signal to the receiver means, and the controller means including calibration means for calibrating the output from the receiver.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.