NF ZM2371, Instruction Manual

Page: 119 / 255

4.8 Using the DC Bias
4-32 ZM2371/ZM2372

Applying the high DC bias voltage
To apply the high bias voltage beyond 2.5V onto the DUT, external power is required. In this
case, insert the capacitance in series between H
CUR
terminal and H
POT
terminal so that the
AC voltage and current may not run through the LCR meter.
Set the DC bias output of
ZM2371 / ZM2372
to OFF.
Element value: the following case shows the example of measurement taken at 100Hz
or more in frequency:
C1 = 200μF (Bipolar electrolytic capacitor)
C2 = 20μF (Film capacitor)
R1 = 1kΩ (R2 = 1 kΩ, R3 = 1MΩ)
When you greatly change the bias voltage while the DUT is being connected: if the
switch S1 is closed temporarily, the charge-/discharging time of C2 can be shortened.
Open the S1 during measurement. If you need the C2 to be remained in
charged state while the DUT is not being mounted, use the R3
Figure 4
–7 External voltage bias circuit
If great measurement error occurs during measurement of the low frequency or small
impedance, increase the capacitance of C1 and C2. In the high frequency and high
impedance case, the load correction is useful.
In case of measurement of the large capacitance, if the impedance of DUT is excessively
lower than the output impedance of LCR meter, decrease the R1 to 100Ω as an example,
so that the charge-/discharging time of DUT can be shortened.
However, the charge-/discharging current are increased by just that much.
The charge-/discharging current of DUT run through the L
CUR
terminal of LCR meter.
Therefore, if the bias voltage is suddenly changed, the current sensing circuit of LCR meter
is temporarily saturated and it is possible to disable the measurement. The bias voltage
should be changed little by little to prevent a great amount of current from running.
R1 should be set to the value excessively higher than the parallel value between the output
impedance of LCR meter and the impedance of DUT. Otherwise, the signal level decreases,
thereby resulting in a terrible measurement error.
R1
C1
C2
R2
S1
H
CUR
H
POT
L
POT
L
CUR
LCR meter
DC blocking circuit
DC bias
Voltage source
D
U
T
R3