Circuit arrangement for the transmission of measurement value signals

Claim 2

A circuit arrangement for coupling a measuring transducer to a remote receiver via a two-wire circuit which two-wire circuit at the same time supplies electric power from a remote voltage source for the operation of the measuring transducer, the circuit arrangement comprising, at the measuring transducer end of the two-wire circuit, first and second terminals coupled to the two-wire circuit, a current switch and a voltage controller connected to said first and second terminals of the two-wire circuit, third and fourth terminals connected to the measuring transducer to supply electric power thereto, said voltage controller being responsive to the voltage supplied between said first and second terminals of the two-wire circuit for converting said voltage into a constant voltage which it applies to said third and fourth terminals, said measuring transducer producing a frequency-analog measurement signal whose frequency is determined by the quantity measured by the transducer, electric power storage means, means including the current switch for charging the electric power storage means with current pulses taken from the remote voltage source, said current pulses having a repetition frequency equal to the frequency of the frequency-analog measuring signal so that the frequency of said current pulses is a measure of the transducer measurement-value signal, a current generator, and means including said current generator for coupling the power storage means to said third and fourth terminals so that the power storage means supplies a part of the operating current of the measuring transducer.

Claim 3

A circuit arrangement as claimed in claim 1, characterized in that the power storage means supplies approximately half the transducer operating current via the current generator.

Claim 4

A circuit arrangement as claimed in claim 1, characterized in that the power storage means comprises a capacitor.

Claim 5

A circuit arrangement as claimed in claim 3, characterized in that the capacitance of the capacitor is so high that at the minimum frequency of the measurement-value signal the voltage variation across the capacitor is smaller than 10% of the average voltage across the capacitor.

Claim 6

A circuit arrangement as claimed in claim 4, characterized in that the capacitor has first and second terminals and the current generator comprises an ohmic resistor connected between the first terminal of the capacitor and said third terminal, and means connecting the second capacitor terminal to said fourth terminal.

Claim 7

A circuit arrangement as claimed in claim 1 characterized in that the on-time of the current switch is approximately equal to the off-time.

Claim 8

A circuit arrangement as claimed in claim 1 wherein the amplitude of the current pulses is adjustable.

Claim 9

A circuit arrangement as claimed in claim 1 wherein the operating current of the measuring transducer is adjustable.

Claim 10

A circuit arrangement that couples a remotely located measuring transducer to a receiver via a two-wire circuit, said circuit arrangement comprising, first and second terminals located at the transducer end of the two-wire circuit and coupled to the two-wire circuit to receive an operating voltage and current for the transducer via the two-wire circuit, third and fourth terminals adapted to be coupled to the measuring transducer, a voltage controller with input means coupled to said first and second terminals and output means coupled to said third and fourth terminals whereby the voltage controller is responsive to the operating voltage supplied to said first and second terminals for converting said voltage into a constant voltage at said third and fourth terminals, an electric storage means, a current switch coupling said first and second terminals to said electric storage means, said transducer producing a frequency-analog measuring signal at a fifth terminal, means coupling said fifth terminal to the current switch for operating said switch at the frequency of the frequency-analog measuring signal and thereby charging said electric storage means by means of a current supplied via said two-wire circuit and at the measuring signal frequency whereby the frequency of the current pulses supplied via the two-wire circuit is a function of said frequency-analog signal, a first current generator, and means including said first current generator for coupling the electric storage means to the third and fourth terminals so that the storage means supplies a part of the transducer operating current.

Claim 11

A circuit arrangement that couples a remotely located measuring transducer to a receiver via a two-wire circuit, said circuit arrangement comprising, first and second terminals located at the transducer end of the two-wire circuit and coupled to the two-wire circuit to receive an operating voltage and current for the transducer via the two-wire circuit, third and fourth terminals adapted to be coupled to the measuring transducer, a voltage controller with input means coupled to said first and second terminals and output means coupled to said third and fourth terminals whereby the voltage controller is responsive to the operating voltage supplied to said first and second terminals for converting said voltage into a constant voltage at said third and fourth terminals, an electric storage means, a current switch coupling said first and second terminals to said electric storage means, said transducer producing a frequency-analog measuring signal at a fifth terminal, means coupling said fifth terminal to the current switch for operating said switch at the frequency of the frequency-analog measuring signal and thereby charging said electric storage means by means of a current supplied via said two-wire circuit and at the measuring signal frequency whereby the frequency of the current pulses supplied via the two-wire circuit is a function of said frequency-analog signal, a first current generator, and means including said first current generator for coupling the electric storage means to the third and fourth terminals so that the storage means supplies a part of the transducer operating current.

Claim 12

A circuit arrangement as claimed in claim 9 wherein said current switch comprises a transistor having its emitter-collector circuit coupled between said first and third terminals, a switching device operated in synchronism with the frequency-analog signal, and a second current generator coupled to the second terminal and to a control electrode of the transistor via said switching device.

Claim 13

A circuit arrangement as claimed in claim 10 wherein the first current generator comprises a resistor, said resistor being connected in series with said transistor between said first and third terminals, and said electric storage means comprises a capacitor having one terminal connected to a junction formed between the transistor and resistor and having a second terminal connected to said second terminal.