WIKA TC12-M - Handbuch (Seite 32)

GB
9. Calculation examples ... / 10. Maintenance and cleaning
14083458.01 09/2013 GB/D
WIKA operating instructions models TR12, TC12 (Ex i) 32
Additional information:
Temperature class for T3 = 200 °C
Safety factor for type-tested instruments (for T6 to T3) = 5 K
Safety factor for type-tested instruments (for T1 to T2) = 10 K
Safety factor for applications for instrument category 1 (zone 0) = 80 % finds no application
here.
9.2 Example calculation for variant 2 with TC sensor
Under the same conditions it gives a lower value for the self-warming, since the supplied
power is not only converted at the sensor tip, but rather over the entire length of the
measuring insert.
Thermal resistance [Rth in K/W] from table = 3 K/W
Self-heating: 0.8 W x 3 K/W = 2.4 K
T
max
= T
M
+ self-heating: 150 °C + 2.4 °C = 152.4 °C
As safety margin for type-examined instruments (for T6 to T3), an additional 5 °C must be
subtracted from the 200 °C; hence 195 °C would be permissible. This means that in this
case temperature class T3 is not exceeded.
This example shows that the self-heating is almost negligible here.
10. Maintenance and cleaning
10.1 Maintenance
The thermometers described here are maintenance-free.
Repairs must only be carried out by the manufacturer.
10.2 Cleaning
CAUTION!
■ Prior to cleaning, disconnect the electrical connections properly.
■ Clean the instrument with a moist cloth.
■ Electrical connections must not come into contact with moisture.
■ Wash or clean the dismounted instrument before returning it, in order to
protect persons and the environment from exposure to residual media.
■ Residual media in the dismounted instrument can result in a risk to persons,
the environment and equipment. Take sufficient precautionary measures.
For information on returning the instrument see chapter 12.2 “Return”.