CURRENT TRANSMITTER CIRCUITRY TO PROVIDE AN OUTPUT VARYING AS THE SQUARE ROOT OF A MEASURED VARIABLE CONDITION

• US 3,854,039 A
• Filed: 04/30/1973
• Issued: 12/10/1974
• Est. Priority Date: 04/30/1973
• Status: Expired due to Term

• Current Assignee: Leonardo V. Serrano
• Original Assignee: Leonardo V. Serrano
• Inventors: Serrano, Leonardo V.
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US05/355,816
• Time in Patent Office: 589 Days
• Field of Search: 235/193.5,151.34,194 328/144 73/205
• US Class Current: 702/47
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G06G 7/20 for evaluating powers, roots, polynomes, mean square values, standard deviation G06G7/122, G06G7/28 take precedence; gamma correction in television systems H04N5/20, H04N9/69
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

A transmitter used in a variable parameter process which provides a current signal varying as the square root of the measured variable and is also particularly applicable to such transmitters of the '"'"''"'"''"'"''"'"'two-wire'"'"''"'"''"'"''"'"' type where the transmitter supply current is controlled by the transmitter to vary as a function of the variable parameter.

Claims

1. A two wire current transmitter having first and second terminals for connection to a power source and to deliver a current signal proportional to the square root of a parameter including first means to provide an input signal which varies as a function of the parameter, a current control circuit providing a variable output current signal in response to a control signal, a squaring circuit having input means providing a first current signal which is a function of said variable output current signal and including second means providing a second signal proportional to the square of said first current signal, a comparison amplifier having an input coupled to the first means and second means and having an output providing a control signal which is a function of the input signal and the second signal, and means connecting the output of said comparison amplifier to provide said control signal to said control circuit and means connected to said first means, said control circuit, said squaring circuit and said comparison amplifier, respectively, to provide power therefore solely through said first and second terminals.

2. A transmitter to deliver a signal proportional to the square root of a parameter including first means to provide an input signal, a control circuit providing a variable output signal in response to a control signal, a squaring circuit having input means providing a first signal which is a function of said variable output signal and including second means providing a second signal proportional to the square of said first signal, a comparision amplifier having an input coupled to the first means and the second means and having an output providing a control signal which is a function of the input signal and second signal, means connecting the output of said comparison amplifier to provide the control signal to said control circuit, switch means, means connecting a first side of said switch means to one input of said comparison amplifier, means connected to the second side of said switch means to provide a signal which is a function of the variable output signal, and means responsive to said input signal to close said switch means to connect the first and second sides thereof when the input signal is below a desired level.

3. A transmitter to deliver a signal proportional to the square root of a parameter including first means to provide an input signal;

a control circuit providing a variable output signal in response to a control signal;

a squaring circuit having input means providing a first signal which is a function of said variable output signal and including second means providing a second signal proportional to the square of said first signal comprising photosensitive resistance means connected in circuit so that the value of said photosensitive resistance means affects said second signal, a light source, the intensity of which is variable to correspondingly change the value of said photosensitive resistance means, anD means controlling said light source so as to change the intensity thereof as a function of said variable output signal and the value of the photosensitive resistance means;

a comparison amplifier having an input coupled to the first means and second means and having an output providing a control signal which is a function of the input signal and the second signal; and

means connecting the output of said comparison amplifier to provide said control signal to said control circuit.

4. A transmitter to deliver a signal proportional to the square root of a parameter including first means to provide an input signal, a control circuit providing a variable output signal in response to a control signal, a squaring circuit having input means providing a first signal which is a function of said variable output signal and including second means providing a second signal proportional to the square of said first signal, said squaring circuit comprising a photosensitive resistance means and a variable intensity light source, the intensity of which controls the value of said photosensitive resistance means, a circuit amplifier having first and second inputs and an output controlling the intensity of said light source, a first input of said circuit amplifier being connected to said input means to receive said first signal, said input means further comprising means providing a signal to a second input of said circuit amplifier which is a function of the value of said photosensitive resistance means, said circuit amplifier adjusting the intensity of said light source to change the value of said photosensitive resistance means to balance the signals at the first and second inputs to said second amplifier, said photosensitive resistance means further comprising a portion of the second means so that said second signal is also a function of said photosensitive resistance means;

a comparison amplifier having an input coupled to the first means and second means and having an output providing a control signal which is a function of the input signal and the second signa; and

means connecting the output of said comparison amplifier to provide said control signal to said control circuit.

5. The transmitter of claim 4 wherein said photosensitive resistance means comprises a single photosensitive resistor, and switching means to alternately couple said photosensitive resistor to an input of said second amplifier and to said second means.

6. The transmitter of claim 1 wherein said input means comprises a feedback signal producing means coupled to be sensitive to the change in the variable output signal.

7. The transmitter of claim 1 wherein said first means comprises a transducer delivering a signal substantially linear with respect to measured pressure differentials in a flowing fluid.

8. The transmitter of claim 4 wherein said first means comprises a capacitance type differential pressure transducer providing an output signal substantially linear with respect to a measured differential pressure.

9. The transmitter of claim 4 wherein said photosensitive resistance means comprises a photosensitve resistor, and first and second resistance networks, switch means to alternately switch said photosensitive resistor into said first and second resistance networks, said first resistance network being coupled with said photosensitive resistor to said second amplifier and said second resistance network comprising at least a portion of said second means and being coupled to said comparison amplifier, said first and second resistance networks being coupled to said switch means to uncouple one network from said photosensitive resistor when the other network is coupled to said photosensitive resistor.

10. The transmitter of claim 9 wherein said transmitter includes power source means for said first and second resistance networks, said first and second resistance networks each having a source impedance and including resistors selected and coupled whereby the source impedances of said first and secoNd networks, when coupled to the photosensitive resistor, are substantially equal at the second amplifier and comparison amplifier respectively.

11. The transmitter of claim 10 wherein said first resistance network comprises a portion of the input means to said squaring circuit.

12. A transmitter to deliver a signal proportional to the square root of a variable input signal, comprising a pair of terminals adapted to provide connection to a power source for said transmitter, a current control amplifier means having a current control input and providing a variable value output current signal through said terminals in response to a control signal at said current control input, a square circuit powered only through said terminals including means responsive to said output current signal to provide a second signal which is proportional to the square of said output current signal, signal comparison means powered only through said terminals including means to sense a difference between said input signal and said second signal and having an output means to provide an output control signal which is a function of said input signal and said second signal, and means to couple the output means of said signal comparison means to said current control input to provide said control signal thereto for controlling the output current signal value and thereby changing the value of said second signal in response to changes of said variable input signal.

13. The transmitter of claim 12 wherein said means to provide a connection to a power source comprises a pair of terminals, said terminals carrying the power for the transmitter and the variable output current signal.

14. The transmitter of claim 13 wherein said squaring circuit includes a light source and a photosensitive resistor responsive to the light source, means controlling the intensity of said light source as a function of said output current signal and a dependent signal, a first network coupled in circuit to provide said dependent signal, a second network coupled in circuit to provide said second signal, and means to alternately connect said photosensitive resistor into said first network and into said second network to thereby change the light intensity and the second signal as a function of the photosensitive resistor value and the output current signal.

15. The transmitter of claim 14 wherein said first and second networks each include resistors selected so that the source impedance of each network is substantially equal when photosensitive resistor is connected in the respective network.

16. A circuit for providing a square root extraction of a substantially linear input signal including amplifier means to provide a variable output signal in response to a control signal, feedback means to provide a feedback signal which is a function of said variable output signal, a photosensitive resistor, a variable intensity light source for controlling the resistance of said photosensitive resistor, first means to control the intensity of said light source as a function of said feedback signal and a second signal, a first network coupled to provide said second signal, a second network coupled to provide a third signal, means to alternately couple said photosensitive resistor into said first network and said second network, respectively, the resistance of said photosensitive resistor and said feedback signal thereby affecting the intensity of said lamp and the resulting impedance of said second network, whereby the third signal is proportional to the square of said output signal, and means connected to said second network to compare said third signal and said input signal and to provide said control signal to said amplifier means as a function of the input signal and the third signal.

17. The circuit of claim 16 wherein said first and second networks each have source impedances, and said networks include resistors selected to provide substantially equal source impedances when said photosensitive resistor is coupled intO the respective network and is of a substantially constant value in each network.

18. The circuit of claim 17 and means to maintain the second signal substantially constant when the photosensitive resistor is coupled to the second network, and means to maintain the third signal substantially constant when the photosensitive resistor is coupled to said first network.

19. The transmitter of claim 1 wherein said squaring circuit input means comprises a current sensitive resistance network connected between said terminals to sense total current through said terminals.

20. The transmitter of claim 1 wherein said squaring circuit input means comprises current sensing means including a voltage divider connected to said squaring circuit, a series combination of a resistance and voltage reference element connected between said terminals, and means to connect said voltage divider in parallel with said series combination.

21. The combination as specified in claim 1 wherein said first means comprises a transducer sensitive to variable physical parameters, and wherein said means connected to provide power to said first means, said squaring circuit and said comparison amplifier includes a voltage reference element connected between said terminals.

22. The transmitter of claim 1, wherein said first means comprises a capacitance type pressure transducer providing an output signal substantially linear with respect to a measured pressure.

23. The transmitter of claim 22 wherein said capacitance type pressure transducer comprises at least one capacitor, an excitation source for said capacitor powered through said terminals comprising an oscillator, means connecting said oscillator to said capacitor including DC coupling means providing DC signals as a function of the capacitance of said capacitor, and means responsive to said DC signals to provide said input signal.