NF ZM2371, Инструкция по эксплуатации

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4.8 Using the DC Bias
4-31 ZM2371/ZM2372

When the signal level is high
The peak voltage that can be outputted by
ZM2371 / ZM2372
is up to approx 7.07V.
It is impossible to set when the total of the peak value of AC measurement signal and DC
bias voltage exceeds the above voltage. If you intend to set the measurement signal level or
DC bias voltage beyond the above limit, it will be set as the permissible maximum value at
that moment.

Settling time for DC bias voltage
The charge-discharging current at early stage of charge-discharging can be suppressed up to
approx 1.4-time that of the max sensing current Ip[Arms] that can be absorbed by the
current sensing section in each measurement range. Therefore, the settling time T
S
[s],
which is determined by the above current value, capacitance C (F) of DUT and change Vc[V]
in Bias voltage, is needed until it can be stabilized within the limited current range.
Ts

C × Vc / ( Ip × 1.4 )
Max sensing current that can be absorbed by the current sensing section

See
“Table 3-3 Max. current, max. voltage and output impedance in each
measurement range”
.
However, from view point of absorbing amount of charge-discharging current, the Ip is:
50μA when the value in table is below than 50μA at frequency
≦
20kHz;
500μA when the value in table is below than 500μA at frequency
≧
20kHz.
Since the charge-discharging current beyond the above value runs through the protection
circuit of L
CUR
/L
POT
terminal, it is possible that the actual settling time can be less than T
S
.
Under the low impedance range (
≦
100Ω) or from the time onward when the limited current
range is achieved after charging/discharging continues in a certain level, the convergence
may occur for the settling time T
stl
[s], which is determined by the time constant, that is, the
output impedance Rd[Ω] and capacitance C[F] of DUT.
T
stl
[s]

7 × C × Rd

When there is a leak current or it takes a long time for charging
When leak current is large due to the low insulation resistance of DUT or when charging
current runs for a long time due to the dielectric absorbing or when it takes a long time for
charging due to the large capacitance, the following symptoms may occur:
・
The bias voltage goes down due to the voltage drop caused by the output impedance and
DC current. It allows the signal voltage sensing section to exceed the operation range,
thereby disabling the correct measurement.
・
The peak of signal current exceeds the permissible range of measurement range, thereby
disabling the correct measurement.
・
Auto selection of measurement range does not work properly.
If the measurement range is fixed to the range where the current running through the DUT
or the peak value of applied voltage can be measured even in the above cases, the impedance
may be able to measure. However, it is afraid that the measurement accuracy may
extremely go down while exceeding the recommended measurement range.

Applying a small DC bias current through the Inductor
If a bias current falls within a small range that the
ZM2371 / ZM2372
can supply, the
impedance may be able to measure while the DC Bias current is running by fixing the
measurement range to the range where “Bias c Peak value of AC measurement
current” can be measured. The Bias current can be adjusted by changing the Bias voltage.
Once the measurement level or measurement frequency is changed, the measurable range is
also changed.