Electronic circuit using digital techniques for vortex shedding flowmeter signal processing

• US 4,463,612 A
• Filed: 12/10/1981
• Issued: 08/07/1984
• Est. Priority Date: 12/10/1981
• Status: Expired due to Term

• Current Assignee: Elsag International NV
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Thompson, William L.
• Primary Examiner(s): Goldberg, Gerald
• Assistant Examiner(s): WILLIAMS, HEZRON
• Application Number:
  US06/329,500
• Time in Patent Office: 971 Days
• Field of Search: 73/861.22, 73/861.24, 73/861.34, 324/78 J
• US Class Current: 73/861.22
• CPC Class Codes: G01F 1/3287 circuits therefor

Abstract

A circuit for processing the vortex shedding frequency signal of a vortex shedding flowmeter comprises a phase detector, switch and low pass filter connected in series. The phase detector receives the vortex shedding frequency and applies it over the normally closed switch to the low pass filter which produces an analog signal corresponding to the frequency of the vortex shedding frequency signal. A voltage controlled oscillator is connected between an output of the low pass filter and an input of the phase detector for tracking the vortex shedding frequency and producing a tracking frequency signal which is maintained when the vortex shedding frequency signal disappears. A range or gain code circuit portion is connected for establishing a set time period during which the frequency signal is accumulated in a counter. The accumulated signal from the counter is utilized as a digital signal corresponding to the vortex shedding frequency signal.

Claims

1. A circuit for processing the vortex shedding frequency signal of a vortex shedding flowmeter comprising;

a phase detector for receiving the vortex shedding frequency signal and providing an output signal corresponding thereto;

a low pass filter for receiving the output of the phase detector and producing an analog voltage signal corresponding thereto;

a voltage controlled oscillator connected to an output of the low pass filter for generating a tracking frequency signal corresponding to the vortex shedding frequency signal;

means connected to an output of the voltage control oscillator and the low pass filter for providing a frequency signal and an analog signal; and

means connected to said phase detector for disabling the operation of the phase detector whenever the vortex shedding frequency signal disappears to maintain the last tracking frequency signal in said phase detector from said voltage controlled oscillator including an electronic switch connected between an output of the phase detector and the input of a low pass filter which is normally closed and a signal dropout detector connected between the input of the phase detector and said switch for detecting the disappearance of the vortex shedding frequency and opening the switch upon such disappearance.

2. A circuit for processing the vortex shedding frequency signal of a vortex shedding flowmeter comprising:

a phase detector for receiving the vortex shedding frequency signal and providing an output signal corresponding thereto;

a low pass filter for receiving the output of the phase detector and producing an analog voltage signal corresponding thereto;

a voltage controlled oscillator connected to an output of the low pass filter for generating a tracking frequency signal corresponding to the vortex shedding frequency signal;

means connected to an output of the voltage control oscillator and the low pass filter for providing a frequency signal and an analog signal;

accumulator means connected to said voltage controlled oscillator for receiving the tracking frequency signal;

timing means connected to said accumulator means for activating said accumulator to accumulate the tracking frequency signal during a selected time period with said accumulator means having digital output lines for generating a digital signal corresponding to the accumulated tracking frequency signal; and

said timing means including a plurality of resistors connected in series, each having series-connected electronic switch, means for selectively opening said switches for establishing a selected resistance across said plurality of series-connected resistances, a resistor connected to said series-connected resistance, means connected to said connected resistances for producing a current which is proportional to an equivalent resistance formed by said connected resistances, a capacitor connected to said current producing means for charging to a selected level voltage at a time which depends on the current supplied by said current producing means and comparator means connected between said capacitor and said accumulator means for activating said accumulator means during the time that said capacitor charges to said selected voltage.

3. A circuit according to claim 2 wherein said comparator means comprises a comparator amplifier having one input connected to said capacitor and another input connected to a source of said selected voltage, an output of said comparator amplifier connected to said accumulator for activating said accumulator.

4. A circuit according to claim 3, wherein said current producing means comprises a double transistor having emitters connected to said resistances, one collector connected to said capacitor and another collector connected to a resistance.

5. A circuit according to claim 4, including a switch connected in parallel to said capacitor and having a control connection to the output of said comparator amplifier for closing when the voltage of said capacitor reaches said selected voltage to apply a zero voltage to said capacitor.