Sensor measurement error
There are a number of sensors ( 2, 22 ) such as thermocouples which can provide a putative measurand signal which is within a predicted range for such signals whilst the sensor is incorrectly operating, such as as due to an open circuit. Techniques and processes are available to determine by interrogation sensor operational validity, but these can distort the measurand signal if correct. By time division multiplex techniques the present arrangement takes a putative measurand signal from a sensor ( 2, 22 ) in order that either within the same time division or more normally a separate time division, an interrogation of the sensor is performed in order to determine accuracy and therefore validity of the sensor 22 . In such circumstances, the putative measurand signal from the sensor 22 is dynamically verified by the interrogator 23 to allow greater confidence with respect to interpretation, if an invalid sensor operation is determined, then a pre-defined value for that sensor failure can be output for the data signal.
1. A method of determining thermocouple integrity with a measurement arrangement comprising a thermocouple, a controller or processor, a digital multiplexer and a test circuit; the method comprising:
(a) the controller or processor taking a temperature reading from the thermocouple using a first circuit,
(b) the controller or processor switching on or off the digital multiplexer,
(c) the controller or processor receiving a signal utilizing the first circuit that is indicative of the temperature reading from the thermocouple,
(d) the controller or processor activating the test circuit upon receipt of the signal in order to determine validity of the signal,
(e) the test circuit, upon being activated by the controller or processor, sending an electric current to the thermocouple via a second circuit that is switched on and off to provide a test reading,
(f) interrogating the test reading to check for the thermocouple being a closed or an open circuit to determine thermocouple integrity and the validity of the signal, and
(g) accepting or rejecting respectively the temperature reading taken by the controller or processor by:
predicting a result of the electric current passed along rails of the second circuit through the thermocouple and electrical resistances;
interrogating the test reading; and
if the result of the electric current is correctly predicted, the temperature reading taken by the controller or processor is accepted.
2. The method of claim 1 wherein the measurement arrangement comprises a plurality of thermocouples, the method further comprising taking the temperature reading and test reading of each thermocouple in sequence.
3. The method of claim 1 further comprising taking the temperature reading and test reading of the thermocouple in a predetermined time period.
4. The method of claim 2 wherein switching on or off the digital multiplexer causes faulty thermocouples to be dynamically switched on or off depending on their integrity to reduce any possibility of interference with valid signals received from properly working thermocouples.
5. The method of claim 1 wherein once the testing circuit is activated, the testing circuit is only electrically connected to the thermocouple by switching the second circuit on long enough to obtain the test reading, and the second circuit is switched off when the testing circuit is not activated.
6. A thermocouple integrity measurement arrangement comprising:
a thermocouple;
a controller or processor;
a digital multiplexer; and
a test circuit,
the controller or processor being arranged to receive a signal that is indicative of a temperature reading from the thermocouple via a first circuit and to switch on or off the digital multiplexer to the test circuit,
the controller or processor being arranged further to activate the test circuit upon receipt of the signal in order to determine validity of the signal,
the test circuit, upon being activated by the controller or processor, is arranged to input a test signal via a second circuit that is switched on and off to stimulate the thermocouple for the controller or processor to receive a test reading,
the controller or processor arranged to determine whether the test reading is indicative of a closed or an open circuit, which is further indicative of the thermocouple integrity and the validity of the signal, and accepting or rejecting respectively the temperature reading,
the controller or processor is further arranged to predict a result of electric current passed along rails of the second circuit through the thermocouple and electrical resistances in order to determine whether the test reading is indicative of the closed or the open circuit, and
if the result of the electric current is correctly predicted, the temperature reading taken by the controller or processor is accepted.
7. A thermocouple integrity measurement arrangement according to claim 6 further comprising a plurality of thermocouples, the arrangement being capable of taking the temperature reading and test reading of each thermocouple in sequence.
8. A thermocouple integrity measurement arrangement according to claim 6 wherein the controller or processor takes the temperature reading and test reading of the thermocouple in a predetermined time period.
9. A thermocouple integrity measurement arrangement according to claim 7 wherein switching on or off the digital multiplexer causes faulty thermocouples to be dynamically switched on or off depending on their integrity to reduce any possibility of interference with valid signals received from properly working thermocouples.
10. The thermocouple integrity measurement arrangement according to claim 6 , wherein once the testing circuit is activated, the testing circuit is only electrically connected to the thermocouple by the second circuit when a switch is switched on long enough to obtain the test reading, and the second circuit is switched off via the switch when the testing circuit is not activated.