Endress+Hauser iTEMP HART TMT162 Bedienungsanleitung Seite 103

TMT162
Endress+Hauser
of  is based on the disparity between the actual temperature, t
would result from employing only  and  (7):
b
With the introduction of both Callendar' s and van Dusen' s constant, the resistance value can
be calculated correctly for the entire temperature range, as long as one remembers to set 
= 0 for
T > 0 °C (8):
R = R + R
T 0
Conversion to A, B and C
Equation (8) is the necessary tool for accurate temperature determination. However, seeing
that the IEC 751 coefficients A, B and C are more widely used, it would be natural to convert
to these coefficients.
Equation (1) can be expanded to (9):
R
T
and by simple coefficient comparison with equation (8) the following can be determined
(10):
(11)
(12)
The device accepts the coefficients to be specified as , ,  and A, B, C.
Information on the coefficients can be requested from the sensor manufacturers in question.
RT – R
æ
0
-------------------- - l
T – + d
l è
R · a
0
--------------------------------------------------------------------------------------
=
ö T
T
æ
l
-------- - 1
–
è ø
100
T ö T
æ æ
-------- -
-------- - 1
a T d – –
0 è ø è
100 100
2
= R ( 1 + AT BT + –
0
a d
æ
----------- -
A = a +
è
100
a d ·
----------- -
B =
100
a b ·
------------
C =
100
, and the temperature that
l
T T
æ ö
l l
-------- - -------- -
– 1 )
è ø
100 100
3
æ ö
l
-------- -
è ø
100
T ö T
ö æ æ
-------- -
-------- - 1
– b –
ø è ø è
100 100
3
4
100CT + CT )
·
ö
ø
2
4
Appendix
3
ö
ø
103