Hioki 3227 - Page 20

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1.3 Measurements and Working Systems
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(2) Temperature Correction Function
The temperature correction function displays the optional temperature
coefficient resistance value after converting to the resistance value of the
optional temperature. The resistance depends on the ambient temperature,
and it is of little use to measure the resistance while ignoring this
temperature dependence.
In the following expression, the resistance value R
t
and R
t0
corresponds to the
resistance value of t ℃ and the measured subjects of t
0
℃ (resistance
temperature coefficient in t
0
℃ : αt
0
)
R
t
＝ R
t0
× {1＋α
t0
× (t−t
0
)}
The 3227 obtains the correctional resistance value (R
t0
) from calculating the
temperature measured by the temperature probe (t), the resistance value of
the measured subjects (R
t
), the standard temperature (t
0
) and temperature
coefficient (α
t0
) by CPU.
For example, the resistance value of the copper wire that will be 100Ω under
30℃ would be followingly under 20℃.
R
t
R
t0
＝
{1＋α
t0
× (t−t
0
)}
100
＝
{１＋(3930×10
−6
)×(30−20)}
＝96.22
See Section 5.3, "Setting the Temperature Correction" and Section 5.4,
"Executing the Temperature Correction", for how to set and execute the
temperature correction. Also see "Reference Material" at the end of this
chapter.
(3) Temperature conversion function
The temperature conversion function uses the temperature dependence of the
resistance to convert measured resistance values to temperature values and
display them.
According to JIS C4004, the temperature rise can be derived by the resistive
method as follows:
r
t
Δt=
r
0
(T ＋ t
0
) − (T ＋ t)
r
0
: coil resistance under cold conditions
r
t
: present coil resistance
t
0
: ambient temperature when measuring coil resistance under cold
conditions
t: present ambient temperature
T: constant (copper: 235, aluminum: 230)