Instructions

23
7.12 Transient Frequency
The repetition rate of the internally timed transients can be set in terms of frequency or period.
Pressing the Freq or Period soft-key on the Transient menu opens the Frequency and Period
setting menu. A new value can be entered, in the present representation, in the usual manner.
Two soft-keys labelled Freq and Period allow the alternative representation to be chosen. Press
the Back soft-key to return to the transient menu or the
Home key to return to the home screen.
The soft-key label on the transient menu will show either Freq or Period to reflect the most
recent choice of representation.
7.13 Transient Duty Cycle
Pressing the Duty soft-key on the Transient menu opens the Duty cycle setting menu. This
setting specifies the percentage of each repetition spent at the Level A setting, including the
transition from Level B to Level A; the transition back to Level B and the time stable at that
setting occupies the remainder of the cycle.
The available duty cycle range is 1% to 99%, but note that the time duration of each portion of
the cycle must be sufficient for the transition defined by the Slew Rate and Level settings to
occur; otherwise the load will never reach the steady state at the set value before the next
transition in the opposite direction starts. This error condition is discussed below. Press the Back
soft-key to return to the Transient menu or the
Home key to return to the home screen.
7.14 Slew Rate
Pressing the Slew soft-key on the Transient menu opens the Slew Rate setting menu. This Slew
Rate setting sets the slope of the transitions between the two level settings. It applies to all
changes in level whether caused by manual setting, adjustment using the knob, the internal
transient generator or external voltage control. It is also used to determine the rate of rise and fall
when the Slow Start circuit is triggered.
The slew control circuit introduces a small additional error into the accuracy of the level settings,
which varies depending on the actual Slew Rate setting. If the dynamic facilities of the load are
not being used, then the Default soft-key sets the circuit to the calibrated state for best accuracy.
The circuit provides a linear transition in the control value of the active mode, so, for example, in
Constant Power (CP) mode the slew rate is expressed in Watts per microsecond, Watts per
millisecond or (at very slow rates) Watts per second. The shape of the current transition is
therefore not necessarily linear in any mode other than Constant Current (CC).
In addition to the usual numeric prompt this menu also shows the calculated theoretical transition
time considering the present Slew Rate setting and the difference between Level A and Level B.
This theoretical value takes no account of any dependency of the actual transition time on the
source and load characteristics, impedances and interconnection inductance which may occur,
particularly at fast slew rates. The user must ensure that the transition time which results from the
values entered is not shorter than the minimum attainable transition time in the present mode,
which is documented in the Specification. It is emphasised that severe overshoots can occur if
the slew rate is set faster than the combination of source and load is capable of supporting
(which may be slower than the value in the Specification, which applies to optimal conditions),
see the section on ‘Fast Slew Rate Limitations’ section 7.14.2.
To set the slew rate to the minimum attainable transition time in the present mode as
documented in the Specification, press the Optimum soft-key.
Pressing the Range soft-key produces a display of the limits of available slew rate for the present
operating mode. If a slew rate value is entered that falls outside the parameter limit range, an
error message is displayed, followed also by a display of these range limits.