The Continuous Thermocouple is designed to sense temperature increases in areas too large (or important)
to be covered by multiples of typical temperature sensors (e.g. standard 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 temperature existing along their entire length.
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) analog signal to a related temperature in degrees F or C.
Continuous Thermocouple
Continuous Thermocouples generate a measurable voltage like normal thermocouples, however, the measuring junction in a Continuous Thermocouple 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 sensor's entire length. This is due to the large fall in resistance in the insulating material at the heated area.
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 than 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.