Haefely 2830, Руководство пользователя, Страница: 23 / 124

Theory
15
Material Dissipation factor @ 20°C
ε
r
Vacuum 1.0
Acetal
resin (Delrin™)
0.5% 3.7
Air 0.0% 1.00059
Askarels 0.4% 4.2
Kraft paper, dry 0.6% 2.2
Transformer oil 0.02%
2.2 … 2.4
Polyamide (Nomex™)
1.0% 2.5
Polyester film (Mylar™)
0.3% 3.0
Polyethylene 0.05% 2.3
Polyamide film (Kapton™)
0.3% 3.5
Polypropylene 0.05% 2.2
Porcelain 2.0%
6 … 8
Rubber 4.0% 3.6
Silicone liquid 0.002% 2.6
Varnished cambric, dry 1.0% 4.4
Water 100% 80
Ice 1.0%
@ 0°C
88
Note: Tests for moisture should not be made at freezing temperatures because of the 100 to 1
ratio difference dissipation factor between water and ice.
5.5 DC Resistivity
The DC-Resistivity (also called electrical resistivity, resistivity, specific electrical resistance or
volume resistivity) is a measure of strongly a material opposes the flow of electric current. A low
resistivity indicate a material that readily allows the movement of electric charge. The SI unit of the
dc resistivity is the ohm-meter (

m). It is commonly represented by the Greek letter

(rho).
The measurement of dc resistivity of liquids depends on a number of test condition:
a. Temperature
Resistivity is very sensitive to changes of temperature, its dependence on the inverse of the
temperature, expressed in Kelvin,(1/K) is generally exponential. It is therefore necessary to carry
out measurements under sufficiently precise temperature condition.
b. Electrical stress