NF ZM2371, Instruction Manual

Page: 45 / 255

3.4 Connection of DUT
3-15 ZM2371/ZM2372
3.4.3 Precautions on Connection

Handling of shields
Connect the shields (outer conductor) of connection cables, 4 pieces together on the DUT side.
The current that flows from H
CUR
terminal through DUT to the L
CUR
terminal returns to the
H
CUR
terminal through the shield. Measurement will fail unless this return path is provided.
To stabilize reference potential in the voltage detection part, connect the voltage cable shield
and the current cable shield.
Do not connect the connection cable shields to the ground. If grounded, a noise will mix in
due to electromagnetic coupling by a ground loop or common impedance coupling with other
devices.

Electromagnetic interference prevention and electromagnetic susceptibility
improvement
In the cable connection with the DUT, put four coaxial cables together in the vicinity of
measurement terminals of LCR meter, and attach the common mode choke. It can reduce
high-frequency radiation field disturbance received from the periphery, or reversely
disturbance given to the periphery.
Measurement cables (ex. : 1.5D-2V  4 pieces)
LCR meter
DUT
measurement
terminals
Common mode choke
(ex. : ESD-SR-250 NEC TOKIN)

Selection of cables
In the measurement of low impedance such as capacitors having large capacitance, a voltage
drop of L
CUR
cable causes a common mode noise, increasing the measurement error. This
error cannot be corrected by the cable length correction. In a narrow measurement range,
the error can be reduced by the LOAD correction and it is therefore recommended to use
thick and short current cables (particularly for L
CUR
) so as to reduce the resistance of cable
inner conductor to 0.5  or less per cable. Note that the circuit (including probe resistance
and contact resistance) between cables and DUT has similar influence.
In the measurement of high impedance such as capacitors having small capacitance, using
long connection cables increases the error due to electrostatic capacitance of the cables. This
error can be corrected by the cable length correction. However, correctable cables are coaxial
cables of characteristic impedance 50

(capacitance: about 100pF/m) having the specified
length. When the cables used are out of specification or when an error is large due to the
DUT to earth capacitance, the error can be reduced by the LOAD correction only in a narrow
measurement range.
Using the cables exceeding substantially the specified length makes the
ZM2371 / ZM2372
operation unstable due to the influence of resistance value or capacitance of cable inner
conductor, causing the measurement to be failed. Also, if DUT to earth capacitance is large,
the operation may become unstable.
It may not be always true depending on the resistance value of DUT or cables, but a total of
capacitance of four connection cables and capacitance to earth of DUT should be reduced to
2000pF or less.