Arrangement for multiplexing of a plurality of remotely-located capacitive probes

Claim 2

In an instrument for measurement at a recording point of a physical characteristic at a remote location: at the remote location, a circuit connected to a terminal at the recording point to provide an impedance thereat, a capacitive measuring probe whose capacitance varies with changes in said characteristic, said probe being normally connected to said circuit, a fixed calibration capacitor whose capacitance lies near one end of the range of variation of the probe capacitance, and a fixed caliBration capacity whose effective capacitance lies near the other end of the range of variation of the probe capacitance; at the recording point, unitary means connected to said terminal for measuring the impedance provided thereat, and manually-operable switching means for effecting at the remote location, selectively, a substitution of said fixed capacitor for said probe, or a substitution of said fixed capacity for said probe, in said circuit, for calibration purposes.

Claim 3

Instrument according to claim 1, wherein said switching means includes means for alternatively transmitting two operating voltages of different characteristics to the remote location, and voltage-responsive means at said remote location for disconnecting said probe from said circuit and for alternatively connecting said fixed capacitor or said fixed capacity thereto, depending on which of said alternative voltages is received at said remote location.

Claim 4

In a system for measurement at a recording point of a physical characteristic at a selected one of a plurality of remote locations: at each remote location, a circuit connectible to a terminal at the recording point to provide an impedance thereat, a capacitive measuring probe whose capacitance varies with changes in the physical characteristic at the corresponding location, each probe being normally connected to its corresponding circuit, a fixed calibration capacitor whose capacitance lies near one end of the range of variation of the capacitance of the corresponding probe, and a fixed calibration capacity whose effective capacitance lies near the other end of the range of variation of the corresponding probe capacitance; at the recording point, unitary means connected to said terminal for measuring the impedance provided thereat, selector switch means for connecting the apparatus at a selected remote location to the apparatus at the recording point, and manually-operable switching means for selectively substituting either the fixed capacitor at the connected remote location for the probe at that location, or the fixed capacity at the connected remote location for the probe at that location, in the circuit at the connected remote location.

Claim 5

In a system for measurement at a recording point of a physical characteristic at a selected one of a plurality of remote locations: at each remote location, a circuit connectible to a terminal at the recording point to provide an impedance thereat, a capacitive measuring probe whose capacitance varies with changes in the physical characteristic at the corresponding location, each probe being normally connected to its corresponding circuit, a fixed calibration capacitor whose capacitance lies near one end of the range of variation of the capacitance of the corresponding probe, and a fixed calibration capacity whose effective capacitance lies near the other end of the range of variation of the corresponding probe capacitance; at the recording point, unitary means connected to said terminal for measuring the impedance provided thereat, selector switch means for connecting the apparatus at a selected remote location to the apparatus at the recording point, and manually-operable switching means for selectively substituting either the fixed capacitor at the connected remote location for the probe at that location, or the fixed capacity at the connected remote location for the probe at that location, in the circuit at the connected remote location.