Aim-TTI LD400, Инструкция по эксплуатации

Страница: 17 / 54

16
Connecting the Load to the Source
The INPUT terminals of the load must be connected to the source to be tested using sufficiently
low resistance and low inductance connections. Inductance in the interconnection can have a
significant adverse impact on the stability of the source and load combination. The wiring should
be as short and as thick as possible. It is essential that the voltage drop across the connecting
leads is sufficiently less than the source voltage to leave enough working voltage across the load.
This requirement must be met at the load input terminals even if external sensing is employed.
The front panel terminals may be used for currents up to 30 Amps; for higher currents the rear
panel terminals must be used.
The load terminals of the instrument are floating from ground, and may be used at potentials of
up to ± 300 Volts DC from ground. Connection to any AC mains circuit is not permitted. Ensure
that all wiring is safely insulated for the working voltage involved.
Prospective Fault Current
The instrument detects any fault condition and responds by disabling the load by turning off the
power devices. However there is no internal fuse in the load circuit, so the possibility exists of a
high current passing if the external source applies a condition so far beyond the rating of the unit
that a power FET is destroyed, which can sometimes result in the device becoming a short
circuit. If the source is capable of supplying a dangerous level of prospective fault current, and
does not itself contain a fuse or circuit breaker, or cannot be easily turned off, users should
consider adding an external fuse to the circuit, particularly if unattended operation is likely.
External Voltage Sensing
When the load is conducting current there will be a voltage drop in the connecting leads. In order
to obtain the expected load characteristic in any mode other than Constant Current, external
voltage sensing leads should be connected from the terminals of the source to the external sense
inputs on the rear panel of the load. In Constant Current (CC) mode external voltage sensing only
improves the accuracy of the meter readings; it does not affect the behaviour of the load.
To avoid impact on the stability margin do not add phase shift in the sensing circuit; in particular,
the use of decoupling capacitors should be avoided. If the sensing connections are likely to be
subject to RF or magnetic fields, use twisted pair cable with an overall shield. The shield should
be grounded or connected to load negative.
The rear panel
VOLTAGE SENSE SELECT
switch selects between
INT
(internal) and
EXT
(external)
voltage sensing. Note that the internal sensing circuit is always used for the power and voltage
protection circuits.
Caution: The unit is designed to permit up to 6 Volts difference between internal and external
sensing (in order to permit zero voltage operation using an offsetting battery); if this switch is in
the
EXT
position, but the sense terminals are not connected, the unit will not detect the fault
condition until the source voltage exceeds this value. This can result in unexpected operation.
Remote Input Disable
This input is provided for remote override of the
INPUT ENABLE
function of the load, possibly for
safety reasons. It is available in all operating modes of the instrument. It is a fully floating input to
an opto-isolator: apply 3 to 12 volts (observing polarity) to disable the load. The load is only
enabled if this signal is absent and the input has been enabled with the front panel controls.
Switching On
The line POWER ( ) switch is at the bottom left of the front panel. Before switching on (
l
),
check that the line operating voltage of the unit (marked on the rear panel) is suitable for the local
supply. After switching the power on (
l
) the LCD should light and display firmware version
information. Avoid turning off the power until the instrument is fully initialised and the home
screen is displayed.