Tettex MIDAS micro 2883 - Standard Capacitor, Measuring Current & Limits

Theory
15
5.8 Standard Capacitor, Measuring Current &
Limits
To evaluate the expected values of test current, standard capacitor current, the corresponding limiting parameters
and the resulting load range use these basic conditions and rules:
(1) Maximum test voltage shall be less than the nominal
voltage of the standard capacitor.
U
Testmax
≤ U
CN
 Current through standard capacitor CN
NTestCN
CfUI ⋅⋅⋅⋅= π 2
 Current through capacitor Cx
xTestCx
CfUI ⋅⋅⋅⋅=
π 2
(2) Minimum current through standard capacitor CN or test
Object Cx
I
C min
≥ 30 µA
Note: Minimal current through CN (internal) to ensure accuracy
(3) Maximum current through capacitor Cx
I
Cxmax
≤ 180 mA
Note: Maximum current provided by the built in high voltage source
(4) Maximum test voltage **
x
Cx
Test
Cf
I
U
⋅⋅⋅
=
π
2
max
max
(5) Minimum test voltage ***
N
C
Test
C
f
I
U
⋅⋅⋅
=
π 2
min
min
 Test current I
X
through test object C
X
I U
f C X
Test x
= ⋅
⋅ ⋅2
π
(6) Maximum Test current through test object C
X
I
X max
≤ 180 mA
Note: Maximum input current of the “INPUT A, B, HVGND” to avoid overload
(7) Minimum Test current through test object C
X
I
X min
≥ 30 µA
Note: Minimal input current of the “INPUT A, B, HVGND” to ensure accuracy
(8) Limitations based on “Technical Data” (e.g. max supply power, current etc.)
Note: These calculations are valid for capacitive test objects (tan δ = 0). They can also be as a close approximation
for test objects with a tan δ value < 0.01.
* Maximum current trough “C
N INTERNAL
” is limited by 12kV / 100pF ⇒ 470µA @ 50Hz
** The max. output voltage is limited to 12kV. The max. output power can also limit the maximum test voltage
*** if Cx<CN, use Cx in this formula instead
Examples:
C
X
=50nF (tan δ < 0.01), f=50Hz 
kV
F
mA
U
Test
46.11
1050502
180
9
max
=
⋅⋅⋅⋅
=
−
π