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input is enabled. Changing either the load mode or the level range while the input is enabled will
trip a fault detector and cause the input to be disabled before the change is implemented.
Selection of Load Mode
The first action in configuring the unit for a particular application is to choose the load mode,
which determines how the current drawn by the load varies with the applied voltage (V). The
Mode
soft-key on the home screen opens a menu offering the various modes listed in the table
below. More detailed descriptions of the properties of each mode are given in the ‘Application
Notes’ chapter later in this manual.
Changing the mode requires the load input to be disabled, which will be done automatically if not
already done by the user. The display returns to the home screen as soon as a mode is selected.
The available operating modes are:
CC
Constant Current
The current is the Level setting, independent of voltage.
CP
Constant Power
Implements I = W / V where W is the Level setting.
CG
Constant Conductance
Implements I = V * G where G is the Level setting.
CR
Constant Resistance
Implements I = (V – V
dropout
) / R where R is the Level
setting and V
dropout
is the Dropout Voltage setting.
CV
Constant Voltage
The load sinks whatever current is necessary to maintain
the terminal voltage equal to the Level setting.
Level A and Level B Setting and Range Selection
Pressing the
Level
soft-key on the home screen initially opens the level setting prompt for either
Level A or Level B, depending on which was altered last. The right hand soft-keys, labelled
A SET
and
B SET
, can be used to switch the prompt to the other level. If the level being edited is
not currently active in controlling the load, a
Select
soft-key will appear allowing it to be made the
active selection if required. A new numeric value can be entered as described above. Separate
settings for both level values are retained for each operating mode.
There are two ranges for level setting in each of the load operating modes except constant
power. These differ in both the range of values permitted and the entry resolution; the present
values are shown in the number prompt. Pressing the
Range
soft-key opens the range selection
menu, with the presently active range highlighted. The selection can be changed using either the
▲ or ▼ soft-keys or the knob. Pressing the
OK
soft-key implements the new selection. Changing
the range requires the load input to be disabled, which will be done automatically if not already
done by the user. Alternatively pressing the
Cancel
soft-key leaves the range unchanged. In
either case the instrument returns to the level setting menu. Changing from a high resolution
range to a low resolution range may result in the truncation of the set level. If the range is
changed and the set level value exceeds the limits for the new range, the value is updated to the
maximum or minimum of the new range.
The level setting menu remains on screen, allowing further changes to be made, until either the
Back
soft-key or the
Home
key is pressed to return to the home screen.
Dropout Voltage
Pressing the
Dropout
soft-key on the home screen opens the Dropout Voltage setting prompt. In
the usual way this displays the present Dropout Voltage setting, the range in which the new value
can be set, and the maximum resolution of the setting. After entry of the number press either the
mV
or
V
soft-key to implement the setting. Either the
Back
soft-key or the
Home
key returns the
display to the home screen.
The primary purpose of the dropout voltage setting is to protect batteries from excessive
discharge. The load will cease to conduct current when the applied voltage from the source falls
below this setting. Note that this is a dynamic limit, not a latching condition, so if there is any
wiring resistance between the source and the voltage sensing point of the load then there will be
