US4841286A
Expired / Lapsed
US
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Apparatus and method for detection of an open thermocouple in a process control network
Assignee: Honeywell Inc
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Filing: 1988-02-08
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Granted: 1989-06-20
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Expires: 2008-02-08
Abstract
Abstract In a process control network, apparatus and method for periodic testing of a thermocouple element includes a switching mechanism that inserts a circuit with known parameters in series with the thermocouple. Voltages levels with and without the inserted circuit are compared and used to identify a failed or failing thermocouple.
Inventors
- 👤 Karl T. Kummer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 16:38
CPC Classifications
G; G01; G01R; G01R17/00; G01K; G01K7/00; G01K7/02; G01K7/026
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
105 words
Apparatus for verifying operation of a thermocouple, said apparatus comprising: a voltage source having a known potential; a resistor having a known resistance; switch means for periodically inserting a voltage source and a resistor in series with said thermocouple; voltage means for measuring a first and a second voltage level at preselected times during a switch means cycle, said first voltage being measured when said voltage source and said resistor are coupled to said thermocouple, said second voltage level measured when said voltage source and said resistor are not coupled to said thermocouple; and comparison means for comparing said first and said second voltage level.
Claim 2
Dependent Claim
105 words
Apparatus for verifying operation of a thermocouple, said apparatus comprising: a voltage source having a known potential; a resistor having a known resistance; switch means for periodically inserting a voltage source and a resistor in series with said thermocouple; voltage means for measuring a first and a second voltage level at preselected times during a switch means cycle, said first voltage being measured when said voltage source and said resistor are coupled to said thermocouple, said second voltage level measured when said voltage source and said resistor are not coupled to said thermocouple; and comparison means for comparing said first and said second voltage level.
Claim 3
Dependent Claim
23 words
The apparatus for verifying operation of a thermocouple of claim 1 wherein said voltage means includes an integrating analog to digital converter unit.
Claim 4
Dependent Claim
30 words
The apparatus for verifying operation of a thermocouple of claim 1 wherein said voltage means includes a capacitor for filtering random noise and filtering changes resulting from said switching means.
Claim 5
Dependent Claim
28 words
The apparatus for verifying operation of thermocouple of claim 3 wherein operation of said switch means and said voltage means are synchronized by signals from said comparison means.
Claim 6
Independent Claim
116 words
The method of verifying operation of a thermocouple, said method comprising the steps of: periodically inserting a circuit having known parameters in series with said thermocouple; measuring a first voltage level and a second voltage level at preselected times during a cycle determined by said circuit having parameters inserted periodically in series with said thermocouple; and measuring said first voltage level when said circuit having known parameters is coupled to said thermocouple; and measuring said second voltage level when said circuit having known parameters is not coupled to said thermocouple; and comparing a first voltage level measured at a first preselected time during said cycle with a second voltage level measured at a second preselected time.
Claim 7
Independent Claim
116 words
The method of verifying operation of a thermocouple, said method comprising the steps of: periodically inserting a circuit having known parameters in series with said thermocouple; measuring a first voltage level and a second voltage level at preselected times during a cycle determined by said circuit having parameters inserted periodically in series with said thermocouple; and measuring said first voltage level when said circuit having known parameters is coupled to said thermocouple; and measuring said second voltage level when said circuit having known parameters is not coupled to said thermocouple; and comparing a first voltage level measured at a first preselected time during said cycle with a second voltage level measured at a second preselected time.
Claim 8
Dependent Claim
26 words
The method of verifying operation of a thermocouple of claim 5 further comprising the step of including a voltage source in said circuit having known parameters.
Claim 9
Dependent Claim
39 words
The method of verifying operation of a thermocouple of claim 6 further comprising the step of selecting parameters of said circuit having known parameters and other circuit parameters wherein equilibrium voltage conditions are not obtained during said periodic coupling.
Claim 10
Dependent Claim
27 words
The method of verifying operation of a thermocouple of claim 7 further comprising the step of measuring said voltage levels by an analog to digital converter unit.
Claim 11
Dependent Claim
36 words
The method of verifying operation of a thermocouple of claim 8 further comprising the step of comparing said first and said second voltage levels, wherein said comparing step identifies failure or uncertain operation of said thermocouple.
Claim 12
Dependent Claim
39 words
The method of verifying operation of a thermocouple of claim 7 further comprising the step of coupling a capacitor to said thermocouple, said capacitor retarding transient voltage response to said coupling and uncoupling of said circuit having known parameters.
Claim 13
Dependent Claim
110 words
Apparatus for verifying operation of a thermocouple, said apparatus comprising: a test circuit including a known voltage source and a known resistance coupled in series; first switch means for coupling said test circuit to said thermocouple at a first node; amplifier means for providing an output signal related to a selected property of a signal applied to an input terminal; second switch means for coupling said first node to said input terminal of said amplifier means; a first resistance coupled to said first node; a capacitor coupled to said first resistor at a second node; and third switch means for coupling said second node to said amplifier means input terminal.
Claim 14
Dependent Claim
110 words
Apparatus for verifying operation of a thermocouple, said apparatus comprising: a test circuit including a known voltage source and a known resistance coupled in series; first switch means for coupling said test circuit to said thermocouple at a first node; amplifier means for providing an output signal related to a selected property of a signal applied to an input terminal; second switch means for coupling said first node to said input terminal of said amplifier means; a first resistance coupled to said first node; a capacitor coupled to said first resistor at a second node; and third switch means for coupling said second node to said amplifier means input terminal.
Claim 15
Dependent Claim
23 words
The apparatus for verifying operation of a thermocouple of claim 11 wherein said amplifier means includes an integrating analog to digital converter unit.
Claim 16
Dependent Claim
23 words
The apparatus for verifying operation of a thermocouple of claim 12 further comprising comparison means for comparing preselected signals from said amplifier means.
References Cited (Backward Citations)
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