Measuring bridge circuit

• US 3,873,917 A
• Filed: 03/06/1974
• Issued: 03/25/1975
• Est. Priority Date: 03/24/1973
• Status: Expired due to Term

• Current Assignee: Manfred Kreuzer
• Original Assignee: Manfred Kreuzer
• Inventors: Kreuzer, Manfred
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/448,453
• Time in Patent Office: 384 Days
• Field of Search: 324/62,DIG.1
• US Class Current: 324/660
• CPC Class Codes: G01R 17/105 for measuring impedance or resistance

Abstract

The present measuring bridge circuit is especially suitable for a plurality of measuring points. One measuring bridge branch is provided for each measuring point. Selectively operable switching means interconnect each measuring bridge branch, and if desired also at least one compensating bridge branch, to a voltage supply source. In order to compensate for any voltage drops across these selectively operable switching means, supply voltage control means are provided which regulate or continuously adjust the output voltage of the supply voltage source in response to said voltage drop. In an alternate embodiment of the invention, a high impedance complementary half bridge circuit is connected through selectively operable further switching means to the other bridge branches. A control of the supply voltage may be accomplished by means of an amplitude comparing circuit.

Claims

1. A measuring bridge circuit arrangement, comprising a plurality of bridge branches, a respective plurality of measuring points one of which is arranged in each bridge branch, resistance means in each bridge branch, a voltage source providing a supply voltage, supply voltage switching means connected to said supply voltage source and to said bridge branches for selectively interconnecting any bridge branch and said supply voltage source, said resistance means in each bridge branch being connected through said supply voltage switching means to said supply voltage source, voltage tap means located between said resistance means and the respective one of said supply voltage switching means, supply voltage control means connected to said supply voltage source, and feedback circuit means connecting said supply voltage control means to said voltage tap means whereby said supply voltage available at said voltage tap means is adjusted to keep it at a predetermined value.

2. The circuit arrangement according to claim 1, wherein said feedback circuit means comprise feedback switching means and switch control means operatively interconnecting said feedback switching means and said supply voltage switching means for operating said switching means synchroneously with each other.

3. The circuit arrangement according to claim 1, wherein said supply voltage control means comprise amplitude comparing circuit means connected to said voltage tap means, reference voltage means also connected to said amplitude comparing circuit means, and means connecting said comparing circuit means to said supply voltage source for adjusting said supply voltage source in response to a difference value produced by said amplitude comparing circuit means.

4. The circuit arrangement according to claim 1, wherein said supply voltage control means comprise an operational amplifier including an output, an inverting input and a non-inverting input, said supply voltage source being connected to said non-inverting input of said operational amplifier, said output being connected to said supply voltage switching means, and said inverting input of said operational amplifier being connected to said feedback circuit means.

5. The circuit arrangement according to claim 4, comprising input switching means connected between said non-inverting input of said operational amplifier and said voltage supply source.

6. The circuit arrangement according to claim 4, wherein said feedback circuit means comprise selective feedback switching means connected between said inverting input of said operational amplifier and said voltage tap means for selectively connecting said inverting input to any one of a plurality of said voltage tap means.

7. The circuit arrangement according to claim 4, wherein said supply voltage switching means comprise an operational amplifier including a controllable output transistor circuit for interconnecting the respective bridge branch to said voltage supply source.

8. The circuit arrangement according to claim 7, wherein said controllable output transistor circuit comprises a controllable collector output.

9. The circuit arrangement according to claim 7, comprising a measurement diagonal, impedance convertor means and means for connecting said impedance convertor means to said operational amplifier as well as to said measurement diagonal.

10. The circuit arrangement according to claim 1, comprising in addition to said plurality of bridge branches, at least one compensating bridge branch and a respective compensating resistor means in said compensating bridge branch, further switching means connecting said compensating resistor means to said voltage source, further voltage tap means located between said compensating resistor means and said further switching means, said circuit comprising further supply voltage control means Also connected to said voltage source, and further feedback circuit means connecting said further voltage tap means to said further supply voltage control means whereby the supply voltage available at said further voltage tap means is also adjustable to keep it at a predetermined value.

11. A measuring bridge circuit arrangement comprising a plurality of bridge branches, a respective plurality of measuring points one of which is arranged in each bridge branch, a supply voltage source, supply voltage switching means connected to said supply voltage source and to said bridge branches for selectively interconnecting any bridge branch and said supply voltage source, complementary high impedance half bridge circuit means, and further circuit means for effectively interconnecting any one of said bridge branches and said complementary high impedance half bridge circuit.

12. The circuit arrangement according to claim 11, wherein said further circuit means comprise further switching means arranged to selectively interconnect any one of said bridge branches and said complementary high impedance half bridge circuit.

13. The circuit arrangement according to claim 12, wherein said supply voltage switching means and said further switching means comprise semiconductor switching means.

14. The circuit arrangement according to claim 12, wherein said supply voltage switching means and said further switching means comprise operational amplifier means.

15. The circuit arrangement according to claim 11, wherein said supply voltage source comprises a carrier frequency generator providing a carrier frequency supply voltage and connected through said supply voltage switching means to any one of said plurality of bridge branches, said complementary high impedance half bridge circuit means comprising a resonance circuit tuned to said carrier frequency, said resonance circuit comprising an inductive voltage divider and capacitor means connected in parallel to said inductive voltage divider means.

16. The circuit arrangement according to claim 11, wherein said complementary high impedance half bridge circuit means comprise impedance converter means providing a low impedance output for said high impedance half bridge circuit means, said further circuit means connecting said impedance convertor means to a respective one of said bridge branches.

17. The circuit arrangement according to claim 11, wherein said complementary high impedance half bridge circuit means comprise relatively low-resistance resistors and impedance convertor means connected to provide a relatively high impedance input for said half bridge circuit means.

18. The circuit arrangement according to claim 11, comprising in addition to said plurality of bridge branches, at least one compensating bridge branch and a respective compensating resistor means in said compensating bridge branch, said compensating bridge branch being connected to said complementary high impedance half bridge circuit and to said first mentioned bridge branches, voltage control means including amplitude comparing means having a reference input and further input means connected across said complementary high impedance half bridge circuit, said amplitude comparing means having an output connected to said supply voltage source whereby the supply voltage source is controlled in response to amplitude difference values.