Aim TTi LD300 Fonctionnement page 15

Level Control Switch
The LEVEL CONTROL switch selects the level setting mode.
The LEVEL A and LEVEL B settings select constant operation at the value set on the
corresponding LEVEL control.
The TRANSIENT setting enables the internal transient generator. Operation alternates between
the LEVEL A and LEVEL B settings at a rate determined by the settings of the FREQUENCY and
DUTY (%B) controls. The signal passes through the slew rate generator.
The EXTERNAL TTL setting enables the use of an external oscillator or logic signal (connected
to the terminal block on the rear panel) to select the operating level. Operation alternates
between the LEVEL A and LEVEL B settings depending on the level of the external signal (logic
high selects LEVEL B). Following the selection gate the signal passes through the slew rate
generator.
The EXTERNAL VOLTAGE setting enables external analogue voltage control of the load. The
signal applied to the rear panel terminal block determines the level setting, with a scaling factor
of 4 Volts full scale. The signal passes through the slew rate circuit.
Dropout Voltage
The DROPOUT control sets the voltage level below which the load will cease to conduct current.
It does not operate in Constant Voltage mode and has a special effect in Constant Resistance
mode.
This setting is also the threshold for the slow start circuit.
Input Enable Switch
Pressing the latching INPUT ENABLE switch enables the load input.
There is also a remote DISABLE INPUT facility available at the terminal block on the rear panel;
applying +3 to +5 Volts here will disable the input.
The INPUT ENABLE switch must be released to reset the fault latch if it is tripped.
Input Indicator Lamp
A multi colour lamp indicates the operating state of the unit. It is off when the input is disabled. It
shows green in normal operation, or orange if the input is enabled but the power stage is
saturated (because there is insufficient voltage for the required current to flow). It shows red if a
fault condition exists; the INPUT ENABLE switch must be released to reset this condition.
Slow Start
The setting of the SLOW START switch determines the behaviour of the unit when it starts to
conduct, either because the INPUT ENABLE switch is pressed while the source voltage is
already present, or because the source is switched on after the load is already enabled. If the
SLOW START switch is not engaged, the load will conduct the full current immediately (without
the control of the slew-rate circuit). If the SLOW START switch is engaged, the load will not
conduct any current until the source voltage reaches the dropout voltage setting; it will then ramp
up to the LEVEL setting at a rate determined by the settings of the SLEW RATE controls.
Transient Frequency
The FREQUENCY control and the associated three-position range switch set the frequency of
the internal oscillator.
Duty Cycle
The setting of the DUTY (% B) control determines the percentage of the oscillator period that the
load is at the LEVEL B setting. The duration of the slewing time from the LEVEL A state to the
LEVEL B state is included in this value.
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