Differential measuring system

• US 4,201,088 A
• Filed: 12/04/1978
• Issued: 05/06/1980
• Est. Priority Date: 12/04/1978
• Status: Expired due to Term

• Current Assignee: YSI Incorporated (Xylem, Inc.)
• Original Assignee: The Yellow Springs Instrument Company Incorporated
• Inventors: Trietley, Harry L. Jr.
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US05/966,261
• Time in Patent Office: 519 Days
• Field of Search: 73/342, 73/362 AR, 73/362.4, 73/362.5, 73/362.6, 323/75 N
• US Class Current: 374/114
• CPC Class Codes: G01D 1/10 giving differentiated values
• CPC Class Codes: G01K 3/08 giving differences of values using thermoelectric elements G01K7/02; giving differentiated values
• CPC Class Codes: G01K 7/16 using resistive elements resistive elements per se H01C, H01L

Abstract

An apparatus for measuring the differential between a plurality of physical quantities, such as temperature, includes transducers 10 and 12 each positioned to sense the physical quantity. The transducers are preferably of the resistive or nonreactive variety. A single, controlled current power source 15 is connected sequentially to the transducers through a switching circuit 20. Each transducer is connected to the switching circuit and to an amplifier 40 through four-conductor cables 35, 45. The amplifier is therefore connected continuously to the transducers to sense both the voltage developed thereacross when the transducer is connected to the source of current through the switching circuit and also to sense continuously any other voltages, such as those that might be produced by thermocouple effects. The output of the amplifier 40 is applied to a linearizing circuit 50 whose output is used to control the magnitude of the output current of the current source 15 in response to the absolute resistance of each transducer. The switching circuit 20 is controlled by a clock 30 the output of which also controls a synchronous demodulator 55 which is connected to the output of the amplifier means for sampling the peak-to-peak output of the amplifier after all transients have decayed.

Claims

1. Apparatus for measuring the differential between a plurality of physical quantities, including

a plurality of transducers for sensing the physical quantities,

a single, controlled power source,

switching means for connecting said power source sequentially to said transducers,

amplifier means,

means for connecting said transducers to said switching means and to said amplifier means,

said amplifier means having inputs continuously connected to said transducers through said connecting means for measuring continuously a signal developed by said transducers and any other signals developed in said transducers and said connecting means, and

output circuit means connected to the output of said amplifier means for indicating the differential between the physical quantities sensed by said transducers.

2. Apparatus for measuring the differential between a plurality of physical quantities, including

a plurality of transducers for sensing the physical quantities,

a single, controlled power source,

means for connecting said power source sequentially to said transducers,

amplifier means,

cable means for connecting said transducers to said connecting means and to said amplifier means,

said amplifier means having inputs connected to said transducers through said cable means for measuring continuously a signal developed by said transducers and other signals developed in said transducers and said cable means,

means for modifying the magnitude of the output of said power source in response to the output of said amplifier means to linearize the output of said amplifier means, and

output circuit means connected to the output of said amplifier means for indicating the differential between the physical quantities sensed by said transducers.

3. Apparatus for measuring the differential between two physical quantities including

first and second transducers placed to sense said quantities,

a constant electrical current source,

means for connecting said current source alternately to said transducers,

amplifier means,

cable means for connecting said transducers to said connecting means and said amplifier means,

said amplifier having its inputs continuously connected to said transducers through said cable means to amplify continuously the voltage developed across each of said transducers as said current source is connected thereto and any other voltages developed in said transducers and said cable means, and

means connected to the output of said amplifier means for indicating the differential output of said transducers.

4. Differential temperature measuring apparatus including

first and second temperature sensing transducers,

a single, controlled current power source,

means for connecting said current source alternately to said temperature sensing transducers,

cable means connected to said temperature sensing transducers for permitting independent placement of said temperature sensing transducers,

amplifier means having its inputs connected to said temperature sensing transducers through said cable means for amplifying continuously the voltage developed across each of said temperature sensing transducers as said current source is connected thereto and any other voltages developed in said temperature sensitive transducers and said cable means,

means responsive to the output of said amplifier means for modifying the magnitude of the current output of said current source to linearize the output of said apparatus, and

means connected to the output of said amplifier means for indicating the temperature differential between said temperature sensing transducers.

5. Differential temperature measuring apparatus including

first and second temperature sensing transducers,

a single, controlled current power source,

clock means for providing a source of control pulses,

switch means responsive to the control pulses from said clock means for connecting said current source alternately to said temperature sensing elements,

cable means connected to said temperature sensing transducers to permit independent placement of said temperature sensing transducers,

amplifier means connected to said temperature sensing transducers through said cable means for amplifying continuously the voltage developed across each of said temperature sensing transducers as said current source is connected thereto and any other voltages developed in said temperature sensitive transducers or said cable means,

means responsive to the output of said amplifier for modifying the magnitude of the current output of said current source to linearize the output of said apparatus,

synchronous demodulator means, connected to the output of said amplifier means and responsive to the control pulses from said clock means, for sampling the peak-to-peak output of said amplifier means after all transients have decayed, and

means connected to the output of said synchronous demodulator means for indicating the temperature differential between said temperature sensing transducers.

6. The apparatus of claim 5 wherein said cable means includes four wires for each transducer, two wires connecting said transducer to said amplifier means, and two wires connecting said transducer to said current source.