9. F.A.Q.’S
73
6. Q. What is the drift of a thermocouple type K?
A. T/C type K can be drifted in several temperature ranges: from 450°C to 550°C or in a measuring
area of 800°C. When you work in a process like ethylene furnaces and your process temperature is
fuctuated between 850°C and 200°C and back to 850°C with an interval of approx. 6 to 8 weeks,
your chosen construction is an industrial thermocouple with a metal sheath into a protection tube of
SS or ceramic. The drift of a thermocouple in this application can be approx. 30°C within one year.
7. Q. What is the response time for thermocouples?
A. Depending on the diameter of the thermocouple itself and the measuring junction (grounded or
ungrounded). When you use mineral insulated thermocouples, the ASTM STP 470 A specifes the
following: ‘Values listed are the average of several mineral insulated elements, checked in each
category. They show the time required to indicate 63.2% of a temperature change. The tests were
performed during a step change from room temperature to boiling water.’
F.A.Q.’S
Diameter
Hot Junction
Time in sec.
1,0 mm
ungrounded
0,3
1,0 mm
grounded
0,1
3,0 mm
ungrounded
1,3
3,0 mm
grounded
0,7
4,8 mm
ungrounded
2,2
4,8 mm
grounded
1,1
6,0 mm
ungrounded
4,5
6,0 mm
grounded
2,0