Load Wire Inductance - Prodigit 34000A Series Operation Manual

36 PRODIGIT
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Load wire inductance

The load wiring has an inductance (L). When the current (I) varies in short time period, It generates
a large voltage at both ends of the wiring cable. This voltage applies to all of the load input terminals
of the 34000A series when the impedance of the EUT is relatively small. The voltage generated by
the load wire inductance (L) and the current variation (I) is expressed using the following equation.
In general, the wire inductance can be measured approximately 1 μH per 1 meter. If the 10 meters of
Load wires is connected between the EUT and the electronic load (34000A Series) with the current
Variation of 2 A/μs, the voltage generated by the wire inductance will be 20 V.
The negative polarity of the load input terminal is the reference potential of the external control signal,
Therefore, the device connected to the external control terminal may get malfunctioned.
When operating under the constant voltage (CV) mode or constant resistance (CR) mode or constant
power (CP), the load current is varied by the voltage at the load input terminal, so the operation can
be affected easily by the generated voltage.
The wiring to the EUT should be twisted and the shortest as possible.
If the load wire is long or has a large loop, the wire inductance is increased. Conse-quently, the
Current variation that results when switching occurs will cause a large voltage drop.
When the value of instantaneous voltage drops under the minimum operating voltage depends on
The generated voltage at the load input terminal, the response of recovery will be extensively
Delayed.
In such event, the electronic load (34000A) may generate unstable oscillation.
In such condition, the input voltage may exceed the maximum input voltage and Cause damage to
The 34000A Series.
E = L x (ΔI /ΔT)
E: Voltage generated by the wire inductance
L: Load wire inductance
ΔI: Amount of Current variation
ΔT: Variation period of current