Computer interface: Standard RS232 interface
Printer: WH-A7 mini-type thermal printer
Environment temperature: -10℃～50℃
Relative humidity: <90%
Overall dimension: 460×360×350mm
Weight: 28kg
VI. Measuring method and principle
There are two measuring methods according to whether tested article is
grounded, namely UST measurement and GST measurement. Their principles
are shown in Diagram 1.
HV output terminal
Icx R HV output terminal
Icx
10KV
o
10KV
o
C
N
I
CN
～
Cx
C
N
I
CN
～
C
X
o
R
N
R
R
N
Cx terminal
(a) UST measurement
(b) GST measurement
Diagram 1
By the side of high-voltage power supply 10kV, the HV is distributed into
two branches, one of which is supplied to internal reference capacitor C
N
.
Dielectric loss of this capacitor is very small and can be basically ignored,
namely pure capacitive current. I
CN
works as the basic standard of capacitive
current. By the side of Cx tested article, the measured current Icx flows to the
instrument through sampling resistor R. Icx can be decomposed into horizontal
component and vertical component, as shown in Diagram 2 and tgδ value can
be determined by calculating ratio of horizontal component and vertical
component.
Cx in Diagram 1(a) is ungrounded tested article. Current of tested article
Icx flows to sampling resistor R though its terminal, then the total current value
10
