TEMPERATURE MEASUREMENT BENCH

 TITLE: TEMPERATURE MEASUREMENT BENCH

Objectives:

· To learn the fundamental temperature measurement techniques using the thermocouple and resistance temperature detector, RTD (Pt-100).

· To compare the accuracy of the various temperature measurement devices.

Theory:

Temperature is the degree of hotness or coldness of a body or environment (corresponding to its molecular activity). It is measured by means of a thermometer or other instrument having a scale calibrated in units called degrees. A temperature scale is determined by choosing two reference temperatures and dividing the temperature difference between these two points into a certain number of degrees. The two reference temperatures used for most common scales are the melting point of ice and the boiling point of water.

The scale we use to measure temperature is "degrees" (°). There are three temperature scales that are used today.

i. The Kelvin (K) scale is used by scientists and for astronomical temperatures.

ii. The Celsius scale (°C) is used in most of the world to measure air temperatures.

iii. The Fahrenheit scale (°F) is used to measure temperatures at or near the surface.

Thermocouple

Thermocouple is a temperature measurement sensor that consists of two dissimilar metals joined at one end (a junction) that produces a small thermoelectric voltage when the junction is heated. Thermocouple thermometers interpret the change in thermoelectric voltage as a change in temperature.

Resistance Temperature Detector (RTD)

A typical RTD consists of a fine platinum wire wrapped around a mandrel and covered with a protective coating. Usually, the mandrel and coating are glass or ceramic based. RTD is wire wound and thin film device that work on the physical principle of the temperature coefficient or electrical resistance of metals. Platinum RTD with a nominal resistance of 100 ohms at 100°C is called Pt-100.

Thermal Heat conduction Apparatus:

The apparatus consists of two thermometers among which one is thermocouple and another is Pt-100. Thermometers are submerged in the electric water heater jug. The temperature of thermometers is digitally shown at the displays.

Procedure

First of all, electric water heater jug was half-filled with water and thermometers were submerged. Then, the heater jug was switched ON. The increasing temperatures of both the thermometer was noted from the respective temperature display on the regular interval of time using stopwatch. This was done until a steady state was achieved and both the sensors showed stable readings.

Observation

Time	Thermocouple Temp. (℃)	Pt-100 Temperature (℃)
0	22	18.0
5	23	18.7
10	24	19.5
15	25	20.8
20	27	22.1
25	28	23.8
30	29	25.5
35	30	26.8
40	32	28.6
45	33	30.1
50	35	32.2
55	36	33.5
60	37	35.4
65	38	37.1
70	40	38.7
75	41	40.1
80	42	42.1
85	44	43.9
90	45	45.5
95	47	47.4
100	48	48.8
105	50	51.1
110	51	53.0
115	54	54.8
120	55	56.5
125	57	58.7
130	59	60.5
135	60	62.5
140	63	64.7
145	64	66.0
150	66	68.0
155	68	69.9
160	70	71.7
165	72	73.9
170	74	75.6
175	76	77.5
180	79	79.7
185	80	81.3
190	81	82.4
195	84	84.1
200	85	85.6
205	87	86.8
210	89	88.1
215	90	89.6
220	91	90.5
225	92	91.3
230	94	91.9
235	94	92.4
240	95	92.9
245	95	93.3
250	96	93.7
255	96	93.9
260	97	94.1
265	97	94.4
270	97	94.7
275	97	94.9
280	97	94.9
285	97	95.1
290	97	95.3
295	97	95.3
300	97	95.4
305	97	95.4
310	97	95.4
315	97	95.5
320	97	95.5
325	97	95.5
330	97	95.5

Graph

From Graph:

The temperature measurement for each temperature measurement device is plotted on a scatter graph with x-axis indicating the time in seconds and the y-axis indicating the temperature in ℃. To differentiate each temperature measurement device the temperatures were plotted on the graph with solid and dashed lines.

Result

The upper limit of the thermocouple and Pt-100 thermometer for measuring the boiling water was found to be about 97℃ and 95.5℃ respectively.

Discussion

For the boiling point data measurement, we can observe that the temperature increases as the time increases for each temperature measurement devices. Comparing the thermocouple and Pt-100 thermometer, the temperatures of both thermocouple and Pt-100 thermometer remains constant at 97℃ and 95.5℃ respectively from 310 to 330 seconds. This comparison shows that the thermocouple thermometer best fit its boiling data temperature measurement and is more accurate compared to the Pt-100. The curve of Pt-100 shows a sharper rise than the curve of thermocouple at the middle which indicates that the Pt-100 is more sensitive than the thermocouple.

Conclusion

From the experiment, the accuracy of the various temperature measurement devices can be compared and analysed and the thermocouple is best for measuring the temperature of the boiling water than the Pt-100.