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六、
Influencing factors of measurement
6.1 Temperature influence
6.1.1
Material conductivity value dependent on its temperature very well, conductivity
values decrease with the increase of temperature usually. Such as copper conductivity
values is 58.0MS/m at 20
℃
, when the temperature rises to 25
℃
, conductivity values is
56.9MS/m. Below is relationship for conductivity, temperature and temperature coefficient.
)
20
(
)
20
(
)
(
1
T
T
σ
σ
a
σ
(T) : Conductivity under the temperature T
σ
(20) :conductivity under the temperature of 20
℃
a :Temperature coefficient of material
T : Temperature of material
6.1.1.1
Temperature coefficient a may refer to Appendix 1.
6.1.1.2
A variety of temperature compensation methods are established to meet the user's
choice of different occasions based on the relationship between the conductivity value , the
temperature and the temperature coefficient of the instrument,
6.1.1.3
The conductivity can be measured accurately when select correct temperature
compensation mode and temperature coefficient.
6.1.2
Summery of the interaction between temperature compensation method, various of
methods and the material temperature coefficient, and how to measure the temperature
coefficient of unknown material.
6.1.2.1
”pseudo temperature compensation”
This is one of the most simple and efficient common modes, measurement or
calibration without taking into account the temperature value and input temperature
coefficient values, as long as meeting the following two conditions.
①
The temperature of the material to be tested shall be the same as the temperature of
the calibration test block. The instrument is calibrated with the value of standard test block
at 20
℃
, and the conductivity value of the unknown material is equal to the compensation
value at 20
℃
.
②
The material to be tested has the same temperature coefficient as the standard block
used for calibration.