Hioki RM3545, Инструкция по эксплуатации, Страница: 318 / 364

Appendix 5 Temperature Conversion (
Δ
T) Function
A6
Utilizing the temperature-dependent nature of resistance, the temperature conversion func-
tion converts resistance measurements for display as temperatures. This method of tem-
perature conversion is described here.
According to IEC 60034, the resistance law may be applied to determine temperature
increase as follows:
Example
With initial resistance
R
1
of 200 m
Ω
at initial temperature
t
1
of 20°C, and final resistance
R
2
of 210 m
Ω
at current ambient temperature
t
a
of 25°C, the temperature increase value is
calculated as follows:
Therefore, the current temperature
t
R
of the resistive body can be calculated as follows:
For a measurement target that is not copper or aluminum with a temperature coefficient of
α
t 0
, the constant k can be calculated using the formula shown for the temperature correc-
tion function and the above formula, as follows:
For example, the temperature coefficient of copper at 20°C is 3930 ppm/°C, so the constant
k in this case is as follows, which shows almost the same value as the constant for copper
235 defined by the IEC standard.
Appendix 5 Temperature Conversion (
Δ
T)
Function
Δ
t
=
R
2
( k +
t
1
)
−
( k +
t
a
)
R
1
Δ
t
Temperature increase [°C]
t
1
Winding temp. [°C, cool state] when measuring initial resistance R
1
t
a
Ambient temp. [°C] at final measurement
R
1
Winding resistance [
Ω
] at temp.
t
1
(cool state)
R
2
Winding resistance [
Ω
] at final measurement
k
Reciprocal [°C] of temp. coefficient of conductor material at 0°C
Δ
t
=
R
2
(k +
t
1
)
−
(k +
t
a
)
R
1
=
210 × 10
-3
(235 + 20)
−
(235 + 25)
200 × 10
-3
= 7.75 °C
t
R
=
t
a
+
Δ
t
= 25 + 7.75 = 32.75 °C
k =
1
α
t 0
−
t
0
k =
1
3930 × 10
-6
−
20 = 234.5