Lab Report Process Instrument 4

SUMMARY

The objective of this experiment was to study the principal and operation of level measurement using thermocouple. And it is also to study the principal and operation of level measurement using RTD & calibration. A thermocouple is a sensor that measures temperature. It is comprised of at least two metals joined together to form two junctions. When heat applied, voltage (mV) is generated the joined produce a thermal electromotive force (emf) when junctions at different temperature. The principle for RTD is every metal is unique composition and has a different resistance to flow electrical current. Most metal, changes electrical resistance directly proportional to change of temperature. It is called temperature coefficient of electrical resistance (TCR). Based on the experiment, thermocouple is more accurate compared to the RTD. It already showed in each table if smaller the deviation difference, more accurate the reading. RTD resistance is varies according to temperature, when temperature increase, the resistance also increase. Various ambient temperatures will affect the accuracy and reliability of RTD, thermocouple type J and K. Variations in ambient temperature also can directly affect the resistance of components in a RTD and the resistance of the reference junction for a thermocouple type J and K.

CONCLUSION

The objective of this experiment was to study the principal and operation of level measurement using thermocouple. And it is also to study the principal and operation of level measurement using RTD & calibration. From this experiment, it concludes that RTD resistance is varies according to temperature, when temperature increases, the resistance also increase. Beside, thermocouple type K and J using a voltage concept which is the difference between the two voltages is proportional to the difference in temperature and can be measured on a voltmeter.

DISCUSSION

The purpose of the experiment was to study the principal and operation of level measurement using thermocouple and also to study the principal and operation of level measurement using RTD & calibration. This experiment was run 4 times with different temperature as for RUN 1 300C, RUN 2 400C, RUN 3 500C and RUN 4 600C. Based on the experiment, thermocouple is more accurate compared to the RTD. It already showed in each table if smaller the deviation difference, more accurate the reading. RTD resistance is varies according to temperature, when temperature increase, the resistance also increase. Beside, thermocouple type K and J using a voltage concept which is the difference between the two voltages is proportional to the difference in temperature and can be measured on a voltmeter. Basically, theory states that for all temperature-measuring devices, RTD is the most stable and the most accurate at moderate temperature. Their output is stronger than that of a thermocouple, they are less susceptible to electrical noise, and they operate on a higher level of electrical signals. Moreover, they are more sensitive and more linear than a thermocouple (output versus temperature), use copper extension wire (not special extension wire), require no reference junction, and are easy to interchange. Radioactive radiation also has minimal effect on RTD since RTD parameter is resistance not voltage (thermocouple). Moreover, thermocouple type K and J have a low sensitivity and limited in accuracy. Thermocouple also are slower in response than RTD. Furthermore, various ambient temperatures will affect the accuracy and reliability of RTD, thermocouple type J and K. Variations in ambient temperature can directly affect the resistance of components in a RTD and the resistance of the reference junction for a thermocouple type J and K. It can be assumed that during the experiment, some errors have been occurred. There are some failures of power supply that cause erroneous reading of RTD. Any small changes like vibration, not tight or corrosion can create error in reading of RTD. RTD also should be more sensitive and accuracy than thermocouple type J and K. By the way, thermocouple type J and K is capable of measuring wider temperature range than RTD and provide a fast response and measure at one specific point.

APPENDICES

Calculation Sample Interpolation y 3  y1 x3  x1  y  y1 x  x1 30  29 1203  1162  29.6  29 x  1162 1 41  0.6 x  1162 1.667 x  1936.667  41 x  1186.36 0 C Average 29  29  29 0 C 2

Temperature Deviation

60.74  60.70  0.04 0 C

TITLE Thermocouple/Rtd Measurement & Calibration.

OBJECTIVE  

To study the principal and operation of level measurement using thermocouple To study the principal and operation of level measurement using RTD & calibration

INTRODUCTION A thermocouple is a sensor that measures temperature. It is comprised of at least two metals joined together to form two junctions. When heat applied, voltage (mV) is generated the joined produce a thermal electromotive force (emf) when junctions at different temperature. In thermocouple have 2 junctions for measuring. It is hot junction and cold junction. Hot junction is the end inserted in the medium to measured temperature while cold junction is connected to measurement device. Voltage generated depends on temperature. Relationship between total circuit voltage (emf) & emf at the junction is,  Circuit emf = Measurement emf – Reference emf The temperature measurement circuit consists a Thermocouple connected directly to Temperature Transmitter. Hot & cold junction can located wherever required to measure temperature differences. Principle for RTD is every metal is unique composition and has a different resistance to flow electrical current. Most metal, changes electrical resistance directly proportional to change of temperature. It is called temperature coefficient of electrical resistance (TCR). RTD is regarded high precision wire wound resistor. By measuring resistance, temperature also can be measure. RTD can detect small variations of resistance temperature transmitter in form of Wheatstone bridge is used. The circuit compared RTD value with three known & highly accurate resistors. Wheatstone bridge consist 3 resistors, voltmeter and voltage source. When temperature increases the voltage also increases.

REFERENCES 1. http://www.surecontrols.com/rtd-vs-thermocouple/ 2. http://en.wikipedia.org/wiki/Resistance_thermometer 3. http://www.engineeringtoolbox.com/thermocouples-d_496.html