Error compensating instrument system with digital communications
First Claim
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1. An error compensating two wire instrument system comprising:
- means for receiving all instrument operating power from a pair of signal wires;
a reference source producing reference signals;
a sensor producing sensor signals which are responsive to physical conditions but are independent of said reference source and signals;
common signal processor means for alternately receiving and processing, in a common signal processing path said sensor signals to provide processed sensor signals and signals including said reference signals to provide processed reference signals;
means for compensating said processed sensor signals by said processed reference signals to produce compensated signals; and
means for generating an instrument output signal in said signal wires in accordance with said compensated signals.
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Abstract
An instrument system provides compensation for signal processing errors by processing both sensor signals and reference signals in a common signal processor. Reference signals may be provided which enable zero compensation, gain compensation, or both. The system outputs compensated signals to a two wire signal loop in either analog or digital form, and selects the form of output signal in accordance with digital input signals received from the signal wires. The system may be embodied as a radio frequency admittance instrument system for monitoring the condition of materials.
56 Citations
22 Claims
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1. An error compensating two wire instrument system comprising:
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means for receiving all instrument operating power from a pair of signal wires; a reference source producing reference signals; a sensor producing sensor signals which are responsive to physical conditions but are independent of said reference source and signals; common signal processor means for alternately receiving and processing, in a common signal processing path said sensor signals to provide processed sensor signals and signals including said reference signals to provide processed reference signals; means for compensating said processed sensor signals by said processed reference signals to produce compensated signals; and means for generating an instrument output signal in said signal wires in accordance with said compensated signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of error compensating an instrument system comprising the steps of:
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receiving instrument operating power from a pair of signal wires; at intervals, processing a sensor signal in a signal processing path comprising said instrument system; processing a reference signal in said signal processing path at intervals alternately with the processing of said sensor signal; and generating a compensated output signal in said signal wires as a function of said processed sensor signal and said processed reference signal. - View Dependent Claims (13, 14)
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15. A two wire radio frequency admittance responsive instrument system comprising:
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means for receiving instrument operating power from a pair of signal wires; sensor means for generating an admittance signal which is responsive to the condition of materials adjacent said sensor; radio frequency signal processing means coupled to said sensor means for generating electrical signal s which are responsive to said sensor admittance signals; input/output means for receiving digital input signals from the signal wires and for transmitting instrument output signals to the signal wires in either analog or digital form; and control means coupled to said signal processing means for receiving said electrical signals and coupled to said input/output means for controlling the receipt of said digital input signals and controlling the transmission of said instrument output signals in accordance with said electrical signals. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification