The response time for a thermocouple is usually defined as the time taken for the thermal voltage (output) to reach 63% of maximum for the step change temperature in question. It is dependent on several parameters including the thermocouple dimension, construction, tip configuration and the nature of the medium in which the sensor is located. If the thermocouple is plunged into a medium with a high thermal capacity and heat transfer is rapid, the effective response time will be practically the same as for the thermocouple itself (the intrinsic response time). However, if the thermal properties of the medium are poor (e.g. still air) the response time can be 100 times greater.
|
Response Time Seconds
|
| Tip Temperature °C-------> |
100 |
250 |
350 |
430 |
700 |
850 |
| Sheath Diameter |
Measuring Junction |
|
|
|
|
|
|
| 6.0mm |
insulated |
3.2 |
4.0 |
4.7 |
5.0 |
6.4 |
16.0 |
| 6.0mm |
earthed |
1.6 |
2.0 |
2.3 |
2.5 |
3.15 |
8.0 |
| 3.0mm |
insulated |
1.0 |
1.1 |
1.25 |
1.4 |
1.6 |
4.5 |
| 3.0mm |
earthed |
0.4 |
0.46 |
0.5 |
0.56 |
0.65 |
1.8 |
| 1.5mm |
insulated |
0.25 |
0.37 |
0.43 |
0.50 |
0.72 |
1.0 |
| 1.5mm |
earthed |
0.14 |
0.17 |
0.185 |
0.195 |
0.22 |
0.8 |
| 1.0mm |
insulated |
0.16 |
0.18 |
0.19 |
0.21 |
0.24 |
0.73 |
| 1.0mm |
earthed |
0.07 |
0.09 |
0.11 |
0.12 |
0.16 |
0.6 |
Values shown are for a closed end sheath. For exposed measuring junctions, divide the values shown by 10.
Table of Typical Thermocouple Response Times. Mineral insulated construction, closed end sheath. Thermocouples with grounded junctions display response times some 20 to 30% faster than those with insulated junctions. |
|
