System, method, and apparatus for detecting air in a fluid line using active rectification
A circuit for detecting air, a related system, and a related method are provided. The circuit for detecting air includes a receiver connection and an air-detection circuit. The receiver connection is configured to provide a receiver signal. The air-detection circuit is in operative communication with the receiver connection to process the receiver signal to generate a processed signal corresponding to detected air. The air-detection circuit includes one or more active-rectifying elements configured to actively rectify the receiver signal to provide the processed signal.
1. A system for detecting air, the system comprising:
a transmitter configured to transduce a driver signal to ultrasonic vibrations;
a receiver configured to receive the ultrasonic vibrations and transduce the ultrasonic vibrations to provide a receiver signal;
an air-detection circuit in operative communication with the receiver to process the receiver signal to generate a processed signal corresponding to detected air, the air-detection circuit comprising at least one active-rectifying element configured to actively rectify the receiver signal to provide the processed signal;
a first conductive path to provide a first polarity of the receiver signal from the receiver;
a second conductive path to provide a second polarity of the receiver signal from the receiver;
a first switch electrically coupled to the first and second conductive paths, the first switch configured to switch a first switch output to between the first and second polarities of the receiver signal, the first switch defining the at least one active-rectifying element;
a second switch electrically coupled to the first and second conductive paths, the second switch configured to switch a second switch output to between the first and second polarities of the receiver signal;
a first amplifier having a positive input and a negative input, wherein the positive input is coupled to the first switch output and the negative input is coupled to the second switch output, wherein the first amplifier provides a first amplifier output in accordance with the positive and negative inputs;
a first filter electrically coupled to the first amplifier output of the first amplifier to provide a first filter output;
a third switch electrically coupled to the first and second conductive paths, the third switch configured to switch a third switch output to between the first and second polarities of the receiver signal;
a fourth switch electrically coupled to the first and second conductive paths, the fourth switch configured to switch a fourth switch output to between the first and second polarities of the receiver signal;
a second amplifier having a positive input and a negative input, wherein the positive input of the second amplifier is coupled to the third switch output and the negative input of the second amplifier is coupled to the fourth switch output, wherein the second amplifier provides a second amplifier output in accordance with the positive and negative inputs; and
a second filter coupled to the second amplifier to provide a second filter output.
2. The system according to claim 1 , wherein the second filter is an integrator.
3. The system according to claim 2 , wherein the integrator is reset after a predetermined period of integration time.
4. The system according to claim 1 , wherein the second filter is a low-pass filter.
5. The system according to claim 1 , wherein at least one of the third and fourth switches are electronically controlled.
6. The system according to claim 1 , wherein:
the first and second switches are configured to receive a first switching signal, the first switching signal and the first and second switches are configured to switch a polarity of an electrical coupling between the first amplifier and the receiver in accordance with the first switching signal; and
the third and fourth switches are configured to receive a second switching signal, the second switching signal has a phase angle of 90 degrees relative to the first switching signal, the second switching signal and the third and fourth switches are configured to switch a polarity of an electrical coupling between the second amplifier and the receiver in accordance with the second switching signal.
7. The system according to claim 6 , wherein at least one of the first switching signal and the second switching signal is a digital signal embodied in a digital circuit.
8. The system according to claim 6 , wherein at least one of the first switching signal and the second switching signal is an analog signal.
9. The system according to claim 6 , wherein the processed signal is a square root of a squared first filter output summed with a squared second filter output.
10. The system according to claim 6 , wherein a processor determines that air exists in a fluid tube when the processed signal is below a predetermined threshold.
11. The system according to claim 10 , wherein the processor estimates a bubble volume using a flow rate of fluid within the tube and a period of time the processed signal is below the predetermined threshold.
12. The system according to claim 1 wherein:
the first and second switches are configured to receive a first switching signal;
the first and second switches switch in response to the first switching signal;
the first and second switches switch such that the first switch output is coupled to the first polarity of the receiver signal about when the second switch output is coupled to the second polarity;
the first and second switches switch such that the first switch output is coupled to the second polarity of the receiver signal about when the second switch output is coupled to the first polarity;
the third and fourth switches are configured to receive a second switching signal;
the third and fourth switches switch in response to the second switching signal;
the third and fourth switches switch such that the third switch output is coupled to the first polarity of the receiver signal about when the fourth switch output is coupled to the second polarity; and
the third and fourth switches switch such that the third switch output is coupled to the second polarity of the receiver signal about when the fourth switch output is coupled to the first polarity.
13. The system according to claim 12 , wherein the first and second switching signals each has a frequency the same as a frequency of the ultrasonic vibrations.
14. The system according to claim 12 , wherein the first and second switching signals each has a frequency the same as a frequency of the driver signal.
15. The system according to claim 12 , wherein the first switching signal has a phase angle of 90 degrees relative to the second switching signal.
16. The system according to claim 12 , wherein the first switching signal has a phase angle of 90 degrees relative to the second switching signal.
17. The system according to claim 1 , wherein the processed signal is a square root of a squared first integrator output summed with a squared second integrator output.
18. The system according to claim 1 , further comprising a processor configured to determine whether air exists when the processed signal is below a predetermined threshold.
19. The system according to claim 1 , wherein the first and second filters integrate for a predetermined number of cycles.
20. The system according to claim 1 , wherein the first integrator integrates for a predetermined number of cycles of the driver signal for a predetermined period of time after the driver signal drives the transmitter such that the ultrasonic vibrations have passed the receiver, wherein a first integrator output is used to adjust an offset of the first integrator.
21. The system according to claim 20 , wherein:
the second integrator integrates for the predetermined period to capture all of the ultrasonic vibrations passing the receiver, and
a second integrator output is used to adjust an offset of the first second.
22. The system according to claim 1 , further comprising
a first integrator, wherein a first switch output and a second switch output are in electrical communication with the first integrator to integrate a signal therefrom to provide a first integrator output,
a second integrator, wherein a third switch output and a fourth switch output are in electrical communication with the second integrator to integrate a signal therefrom to provide a second integrator output,
a first sample-and-hold circuit to hold a voltage of the first integrator output for the processor to determine the processed signal;
a first diagnostic sample-and-hole circuit to hold the voltage of the first integrator output to adjust an offset of the first integrator;
a second sample-and-hold circuit to hold a voltage of the second integrator output for the processor to determine the processed signal; and
a second diagnostic sample-and-hole circuit to hold the voltage of the second integrator output to adjust an offset of the second integrator.
23. The system according to claim 22 , wherein the processed signal is a vector defined by the first integrator output and the second integrator output, wherein a processor is configured to perform an integrity check by determining if a phase angle of the processed signal is within a predetermined range.