BK-130
6-1
SECTION 6: GUARD-GROUND-RETURN CONNECTIONS
The base of the High Voltage transformer contains a currentmeter feature useful in measurement of different
current sources.
(
Refer To Figure 6-1
)
1.
Standard Mode (RTN)
(Use for liner testing)
The standard configuration is set up to measure the current from the high potential side of the unit under
test to ground. This configuration
must
be used if it is not possible to isolate the low voltage side of the
object under test from ground.
The low potential side of the unit under test is connected directly to ground. The binding post Jumper
Clip is installed between the “GND” and the “RETURN” posts on the base of the H. V. Transformer.
This measures the output current flowing from the high voltage output through the unit under test to
ground and the current meter then senses the return current from ground to the “RETURN” terminal of
the high voltage transformer.
2.
Guard Mode
(Use for boom and chassis insulator testing)
For test objects that can be fully isolated from ground it may be desirable to use the Guard Mode. In
this mode only current passing through the test object will be displayed on the current meter. This will
be especially important if very small currents are to be observed.
In this mode the current path does not flow directly to ground from the low potential side of the unit
under test, but flows through the currentmeter first and then to ground.
The connection to be made is (1) connect the low potential side of the unit under test directly to the post
marked RETURN and (2) connect the jumper clip between the GUARD and GND posts. (
NOTE
: The
GND post is internally connected to the GROUND terminal.)
CAUTION
If the test specimen is not fully isolated from ground, the current meter will either not work, or not
display accurate current readings, and this mode should not be used.
