What is reference junction compensation?
What is reference junction compensation?
(b) Cold junction compensation. Cold junction compensation is a process whereby a voltage is added (or subtracted) from the output voltage of the thermocouple so that the reference junction appears to be at 0 °C even if it is not. This may be done electronically using an LM335 precision temperature sensor.
What is reference junction compensation in thermocouple based temperature sensor?
In Summary Cold junction compensation compensates for the missing thermoelectric voltage due to the fact that the thermocouple cold end at the instrument is not at (0°C /32°F). This then allows electronics to use the established thermoelectric voltage tables (or polynomials) to determine the temperature at the hot end.
Why is reference junction compensation necessary in thermocouple?
Cold Junction Compensation (CJC) is necessary when making temperature measurements using thermocouples. CJC becomes necessary because the junction between each end of the thermocouple and your measuring system (connector block, terminal block) also adds a potential difference to the thermocouple voltage.
What is temperature compensation in thermocouple?
The temperature-sensing diode converts the ambient temperature into a voltage. The IC takes this voltage and the thermocouple voltage and calculates the compensated hot-junction temperature. The digital output is the compensated hot-junction temperature measured by the thermocouple.
What is reference junction in thermocouple?
Since the thermocouple is a differential device rather than an absolute temperature measurement device, the reference junction temperature must be known to get an accurate absolute temperature reading. This process is known as reference junction compensation (cold junction compensation.)
What is a thermocouple junction?
Thermocouple junction is the measuring point of a thermocouple sensor, where the positive and negative legs of the thermocouple wire are welded together. It can sometimes be called the Hot end junction, but this is a more general term.
What is CJC in thermocouple?
A thermocouple measurement always needs information from joined wire end (hot junction) and open wire end (cold junction). The cold junction is also called reference point. Variations of reference point temperature are compensated with CJC measuring (Cold Junction Compensation).
What is reference junction?
One of the two junctions in a thermocouple system—the one held at a constant or stable temperature to serve as a reference for measuring the junction.
How is cold junction compensation calculated?
The governing equation for this is: Eemf = −S∆T = S(THOT − TCOLD), where: Eemf is the voltage output of the thermocouple. S is a temperature-dependent material property, known as the Seebeck coefficient (For a type K thermocouple, this is roughly 4.1 μV/°C between 0°C and 1000°C)
When the reference junction is the same temperature as the measurement?
Under these conditions, if the measurement temperature is above 0° C, a thermocouple has a positive output; if below 0° C, the output is negative. When the reference junction and the measurement junction are the same temperature, the net voltage is zero.
What is exposed junction?
Exposed Junctions are a type of thermocouple measuring junction. This type of junction gives a very rapid response time to temperature, but it is unprotected from damage or attack.
What is cold junction in thermocouple?
When a thermocouple or its extension wires are connected to the terminals of a device like a thermocouple transmitter the cold junction is at the room temperature T1°C. If both temperatures of the hot and the cold junctions are above 0°C, the device receives a lower emf than when the cold junction temperature is 0°C.
What exactly is cold junction compensation?
Cold junction compensation is a process whereby a voltage is added (or subtracted) from the output voltage of the thermocouple so that the reference junction appears to be at 0 °C even if it is not. This may be done electronically using an LM335 precision temperature sensor.
What is the working principle of thermocouple?
Thermocouple Working Principle. The voltage is measured to infer the temperature. In practical operation, wires A and B are connected to a digital voltmeter (DVM), digital multimeter (DMM), digital data acquisition system, or some other voltage measuring device. If the measuring device has very high input impedance,…
What is the output of a thermocouple?
A thermocouple is an electrical device that responds to temperature change by a change in voltage output. A thermocouple works to produce a small electrical voltage output by connecting two dissimilar metals or two wires forming a measurement junction at the sensor tip of the device.
