TO MEASURE THE TEMPERATURE BY USING RTD

ABSTRACT:

This manual is about temperature measuring device named as RTD. It is a temperature detector that depends upon a change in electrical resistance It measures the temperature with help of resistance of metal changes RTD most commonly uses platinum metal because of chemical inertness, resistance vs temperature relationship, stability. The element of resistance is the heart of RTD This experiment demonstrates the overall properties and construction of RTD. and the role of RTD system in bridge circuit It also proofs practically to measure the temperature by using RTD.

INTRODUCTION:

It is a transducer which is used for estimating high temperatures The basic characteristic of this temperature sensor is the effect on resistance as temperature increases It has positive coefficients and it is manufactured with platinum wire. Most commonly the NOMINAL RESISTANCE of platinum RTD is 100 ohms at temperature of 0© The tolerances of RTD vary with the standards and manufacturer RTD is required when high precision over a high temperature limit is needed and large degree of standards is demanded Even among the all kinds of temperature measuring devices RTD is one which measures the temperature most accurately and of large range in shorter elapse of time It is a linear device. Platinum is a standard in this system but also metals like NICKEL,  BALCO can be used.

WORKING PRINCIPLE OF RTD:

Electrical resistant thermometers manipulate on principle which demonstrates that when metallic wire heats the electrical resistance can also be increased relatively as temperature increases. The increment in resistance of metallic wire and temperature can be analyzed for any type of wire. In this way, a pierce platinum resistance is supplied together with power supply and network resistance that provides digital indication directly. Properties of temperature supplied are;                             

Resistance at 0© 100 = 0.1ohm   Temperature coefficient 0.385 ohms/©

INSTRUMENTS:

5- Excitation source: Constant current type

6- First stage amplifier: DC Amplifier

7-Second Stage Amplifier: Summing Amplifier adjustment at zero and gain

8- Thermometer

9-Heating unit

10- Water

11- Beaker

EQUIPMENT SETUP:

The setup basically comprises of RTD (Resistance Detective Sensor) and signal observing circuit. In this experiment RTD made up of platinum 100 is used and RTD is covered with stainless steel so that it can be inserted in a GAS or LIQUID to detect the heat. The resolution is maintained at 0.292-0.39 ohm/© The sensor of RTD is connected to the data input of the transmitter amplifier. The current from the amplifier initially incorporates to a small range of value and current is then analyzed as the detecting unit of RTD is heated.

PROCEDURE:

1. As the switch SWg-4 opens, evaluate the resistance of RTD detector at room temperature Estimate across TP49 and TP50
2. Now turn on the 10 ohm resister with SWG-1 switch closes. Give 2-3 minutes for the heating unit for warming and then place RTD step to heating unit and continue to evaluate the resistance of RTD and calculate the value after 1 minute of heating element

Now permit the RTD detector to cool it again. Closes the switch SWG-4 attach the RTD to the base point of the amplifier. The detector is used to maintain the current by means of Amplifier. Now supply the power to 10VDC and set R1 In clockwise position and then attach the meter of 1m A to TP51-TP52.close the switch and now repeat this again to achieve a precise readings and with the help of DMM, evaluate the base bias voltage in between the TP49-TP50.

1. When he detector is placed again next to heating unit the resistance of sensor increases or decreases and also the temperature
2. Now provides the heat to the RTD element for just 1 minute and then record the reading

1. The gain od DC is therefore determined from,

          A (DC) = Vc / Vb

• Now verify the measurements and check how the increase in temperature affects the resistance element
• Use R OF optimum temperature above 0©
• Use the conclusions from step 1 and 2 to estimate the readings and then record it

Observe the temperature increment among the room temperature and heating unit in ©

Table – 1.1

TEMPERATURE COEFFICIENT AND ACCURACY:

It is actually the electrical and physical property of the alloys of metal and the methodology to which this system is fabricated It demonstrates the average resistance per unit temperature increment between ice point and boiling point of water According to ASTM, the temperature range of RTD is measured from -200-650© and RTD is generally known for high precision and accuracy.

ADVANTAGES OF RESISTANCE TEMPERATURE DETECTORS:

• Linearly over large operating limit
• Large temperature operating limit
• Wide temperature operating limit
• Best stability over high temperature

DISADVANTAGES OF RESISTANCE TEMPERATURE DETECTOR:

• Sensitivity is low
• Cost is high than thermocouples
• No point detecting
• Vibration and shock affects the system

APPLICATIONS:

• Stoves and grills
• Micro-electronics
• Exhaust gases estimating temperature
• Petrochemical processing
• Textile and plastic production industries

CONCLUSIONS:

The graph plot between temperature and resistance element is analyzed and observed that it is linear (straight line graph) It is most accurate device for evaluating high temperature and creates analogous analysis also with hybrid approach.