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| WHAT is a CONTINUOUS THERMOCOUPLE? |
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| The Continuous Thermocouple is designed to sense temperature increases, when such increases occur randomly within an area too large (or important) to be covered by multiples of point type temperature sensors (e.g. ordinary thermocouples or RTD's). In order to understand the operation of a Continuous Thermocouple, it is important to understand the theory which made the development of these unique temperature sensors possible. Both FTLD and CT²C have the same operating characteristics and detect the hottest point existing along their entire length. It is important to understand the difference between Continuous Thermocouples and Linear Heat Detectors. A detailed comparison is provided on our Sensor Comparison page. Seebeck Effect Continuous Thermocouple function is based on the long-established "Seebeck Effect", where a circuit formed from two dissimilar wires joined at both ends, develops an emf (voltage) proportional to the difference in the two junction temperatures. Today these junctions are referred to as the measuring junction, and the reference junction.  Standard thermocouple In common practice the wires are joined at one end only to form a point-type temperature sensor known as a "Thermocouple". Instrumentation converts the mV (millivolt) signal to related temperature in degrees F or C.  Continuous Thermocouple Continuous Thermocouples generate a measurable voltage like normal thermocouples, however, the measuring junction is not formed by directly joining the two wires. More remarkably, the measuring junction is not fixed but, when subjected to an increase in temperature, becomes concentrated at the hottest point anywhere along the sensors entire length. This is due to the large fall in resistance in the insulating material. The nature of this insulating material is such that the voltage developed between the two wires always relates to the highest temperature along the cable's length. This is true if the "hot spot" is fixed, as well as if the "hot spot" is moving along the length of the sensor. This phenomenon allows for an infinite number of measuring points along the sensors length.   When the temperature (T1) at any point along the Continuous Thermocouple length exceeds the temperature of the remainder of the cable, the electrical resistance (IR) of the insulating material between the thermocouple wires is reduced at that point and a "temporary" measuring junction forms. If a hotter temperature (T2) occurs at another point on the cable, the IR at that point will be lower that the IR at T1 and a new "temporary" measuring junction forms. The reduced IR at T2 will allow the thermocouple to generate a higher voltage than at T1 and thus the T2 temperature is reported.  |
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