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US 4,841,286 AGranted
Apparatus and method for detection of an open thermocouple in a process control network
AssigneeHoneywell Inc.
InventorKarl T. Kummer
Life of this patent
Estimating the term…
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.
Claims13
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.
3 more elements
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.
5 more elements
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.
5 more elements
Dependencies are inferred from the claim text.