An RTD resistance can be converted into temperature using standard tables that gives values of temperatures for any given resistance value of the RTD.
An example of RTD temperature/resistance determination from the standard tables:
Example 1:
Calculate the resistance of an RTD thermometer when the temperature is:
a) 0 degree Celsius
b) 100 degree Celsius
c) 50 degree Celsius
d) 75 degree Celsius
Solution:
(a) From the Temperature vs Resistance data tables,
At 0 degree Celsius, Resistance = 100 ohms
(b) At 100 degree Celsius, Resistance = 139.16 ohms
(c) At 50 degree Celsius, Resistance = 119.73 ohms
(d) At 700C, resistance = 127.54ohms
At 800C, resistance = 131.42ohms
At 750C, let resistance = X
Using interpolation method, we have:
(70 - 80)/(75 - 80) = (127.54 - 131.42)/(X - 131.42)
-10/-5 = -3.88/(X - 131.42)
-10(X - 131.42) = 19.4
X = 131.42 - 1.94 = 129.48
Example 2:
Solution:
At
0 degree C , RTD resistance = 100Ω
100 degree C, RTD resistance = 139.16Ω
Let X be the temperature of the water when RTD resistance is 120Ω
Using interpolation, we have:
(X - 0)/(100 - 0) = (120 - 100)/(139.16 - 100)
X/100 = 20/39.16
X = (20 X 100)/(39.16)
X = 51.07250C
Hence temperature of the water bath is 51 degree C
For more information on RTD Sensors, check out:
The table below shows temperature versus resistance data in degree celsius with temperature coefficient of resistance of: 0.003916 ohm/ohm/°C.
Fundamental Interval 39.16 ohms
0C
| 0 | 100 | 200 | 300 | 400 | 500 | 600 |
0C
|
| 0 | 100 | 139.16 | 177.14 | 213.95 | 249.59 | 284.04 | 317.33 | 0 |
| 10 | 103.97 | 143.01 | 180.88 | 217.57 | 253.09 | 287.43 | 320.59 | 10 |
| 20 | 107.93 | 146.85 | 184.60 | 221.17 | 256.57 | 290.79 | 323.84 | 20 |
| 30 | 111.87 | 150.68 | 188.31 | 224.77 | 260.05 | 294.15 | 327.08 | 30 |
| 40 | 115.81 | 154.49 | 192.01 | 228.35 | 263.51 | 297.50 | 40 | |
| 50 | 119.73 | 158.30 | 195.70 | 231.92 | 266.96 | 300.83 | 50 | |
| 60 | 123.64 | 162.09 | 199.37 | 235.47 | 270.40 | 304.15 | 60 | |
| 70 | 127.54 | 165.87 | 203.03 | 239.02 | 273.83 | 307.47 | 70 | |
| 80 | 131.42 | 169.64 | 206.69 | 242.55 | 277.25 | 310.76 | 80 | |
| 90 | 135.30 | 173.40 | 210.33 | 246.08 | 280.65 | 314.05 | 90 | |
| 100 | 139.16 | 177.14 | 213.95 | 249.59 | 284.04 | 317.33 | 100 | |
Ω/0C Ave
| 0.390 | 0.380 | 0.368 | 0.356 | 0.345 | 0.333 | 0.325 |
Example 1:
Calculate the resistance of an RTD thermometer when the temperature is:
a) 0 degree Celsius
b) 100 degree Celsius
c) 50 degree Celsius
d) 75 degree Celsius
Solution:
(a) From the Temperature vs Resistance data tables,
At 0 degree Celsius, Resistance = 100 ohms
(b) At 100 degree Celsius, Resistance = 139.16 ohms
(c) At 50 degree Celsius, Resistance = 119.73 ohms
(d) At 700C, resistance = 127.54ohms
At 800C, resistance = 131.42ohms
At 750C, let resistance = X
Using interpolation method, we have:
(70 - 80)/(75 - 80) = (127.54 - 131.42)/(X - 131.42)
-10/-5 = -3.88/(X - 131.42)
-10(X - 131.42) = 19.4
X = 131.42 - 1.94 = 129.48
Example 2:
An RTD with a temperature coefficient of resistance of 0.390 has a resistance of 100Ω at 00C and a resistance of 139.16Ω at 1000C . If the RTD is used to measure the temperature of water in a water bath heater, what is the temperature of the water bath if the resistance of the RTD is 120Ω?
Solution:
At
0 degree C , RTD resistance = 100Ω
100 degree C, RTD resistance = 139.16Ω
Let X be the temperature of the water when RTD resistance is 120Ω
Using interpolation, we have:
(X - 0)/(100 - 0) = (120 - 100)/(139.16 - 100)
X/100 = 20/39.16
X = (20 X 100)/(39.16)
X = 51.07250C
Hence temperature of the water bath is 51 degree C
For more information on RTD Sensors, check out:
