Instrumentation & Measurement Lab Experiments

Study Operation and Technical Specification of Thermocouple

May 28 2023

Apparatus Required:

Thermocouple kit,Thermameter, Beaker, Immersion Rod,

Theory

A thermocouple; is a thermoelectric device that converts thermal energy into electrical energy. The thermocouple is used as a primary transducer for measurement of temperature .It convert’s temperature directly into e.m.f. Three phenomena which govern the behavior of a thermocouple are4 the see beck effect, the Pettier effect and the Thompson effect, While many metals and alloys exhibits the thermoelectric effect, only a small number of them are widely applied for temperature measurement of all the metals used for thermocouples between 630.5°Cand 1063°C.Its sensitivity is only about 6mV/C and is used upto 150°C.Constantine is another alloy that is used with copper ,iron or chromel or choromel .Chopper contantine thermocouple are the maximum sensitivity of 60mV/C and is useful for the range from 200-40°C.

In suction type thermocouple system, the thermocouple is exposed to the hot gas after it is extracted from the hot furnace and made to flow continuously past the hot junction. The thermocouple is provided with a radiation shield so that it does not radiate more heat to the cooler walls of the gases, than that it receivers by radiation.

The immersion type thermocouple system is intended to measure the temperature of hot liquids and gases by immersing it into the medium of the test fluids. For temperature up to 50°C, they are directly used if a rapid indication is desired, otherwise a protecting tube of mild steel of sufficient length is used, and the thermoelectric characterization of the thermocouple wires changes due to oxidation in the test fluids and the wires may be corroded in certain fluids.

Thermocouple is the most commonly used electrical devices for temperature measurement .It is a bimetallic device consistants of two wires. The thermocouple provided with set – up is chromel-Alumed .If the junction of the thermocouple is heated then the thermo – electric emf developed across its terminals depends upon the difference in temperature between its cold and hot junction of thermocouple.

Procedure:-

Connect the 220V AC Power Supply to the Demonstrator through Power Cord.
Keep toggle switch in center position.
Connect DPM positive point TP3& negative point to CND and set 273K at DPM using potentiometer VR3.
Remove positive point of DPM from TP3 and connect it TP2 . Set VR4 to 273+Room temperature.
Now put the mV-°C switch towards C
Now connect DPM positive point to Room Temperature compensation network output. DPM will show the Room Temperature.
Set the Gain Control potentiometer VR2 to anticlockwise.
Connect socket (To DPM) to positive of DPM.
Set mV-°C switch towards mV.
Short the input (Thermocouple) of the set-up with a lead and measure the output on DPM. It must be zero. If not , adjust it to zero with the help of VR1
Connect positive & negative of mV output to positive & negative of good quality DPM. Now set mV output to 10mV using se mV knob.
Remove the input short lead and connect the thermocouple input mV output source.
Adjust 10 on DPM using VR2. Repeat step 10-12 two three for precise calibration.
Remove the mV from the input and connect the thermocouple to their point
Take a beaker provided with instrument & fill it with water .Place a immersion rod in the beaker.
Keep the Thermometer & Thermocosssuple Probe in the beaker.
Keep the Thermometer & Thermocosssuple Probe in the beaker.
Now switch ON immersion rod. The mV generated across its terminals will be displayed on the DPM.
You can measure the temperature of hot water by putting mV C switch towards C.It will display the temperature as thermometer showing
Note down reading of both mV and Temperature (°C) on DPM after a fixe interval in Table
Plot the graph between Temperature (°C) and Thermocouple mV.