Set Current Limit; Instantaneous Current Output - TTI QL Serie Manual De Instrucciones

Set Current Limit

With the output off, the right-hand display shows the current limit to a resolution of 1mA (0·1mA on
the 500mA range).
The current limit can be set directly from the numeric keypad: press the NUMERIC SET I key, enter
the new value using the numeric keys and confirm by pressing OK. The broad principles of keypad
entry are explained in the Initial Operation chapter, which should be read by new users.
When SET I is pressed the display shows 0·000; a new current is then entered (e.g. 1·234A is
entered as 1, · , 2, 3, 4,) and confirmed by OK. The position of the decimal point in the display is
fixed to reduce the risk of entering a wrong value. As a consequence, and to avoid the need to enter
or display leading zeroes (e.g. 0·234A is entered as ·, 2, 3, 4, OK), numbers to the left of the
decimal point are shown slightly differently to the numbers to the right of the decimal point during
number entry; this is self-evident during number entry.
The minimum current setting is 0·001A (0·1mA on the 500mA range); the maximum setting is
3·000A, 5·000A or 500·0mA (QL355), 2·000A, 4.000A or 500·0mA (QL564) according to range, i.e.
there is no over-range capability.
Pressing OK at any point will set the current entered with any remaining digits set to zero,
e.g. 1, ·, 2, OK will set 1·200A; 1, OK will set 1·000A; pressing OK immediately after SET V (while
the display shows 0·000A) will set 0·001A.
Pressing ESCAPE at any time during the sequence, or making no key press within 10 seconds of the
previous one will cause the display to return to its original reading before SET I was pressed.
Entering a value outside the range maximum (including trying to enter 2 digits before the decimal
point) or trying to enter more than 4 digits will cause the buzzer to beep twice; the last key entry will
be ignored.
The current limit can also be set using the rotary jog control. Pressing JOG SET I will illuminate the
key and the JOG indicator under the digit that was last jogged will flash. Whilst the I key is lit, each
further press will move the JOG indicator one digit to the left; the selection 'wraps round' such that
when the largest value of jog increment has been reached the next press returns it to the lowest.
The default position at power-up is under the LSD, i.e. the lowest jog increment is selected. The jog
steps that can be selected are 1mA, 10mA and 100mA (0·1mA, 1mA and 10mA on the 500mA
range).
With jog enabled the current limit can be incremented or decremented with the rotary jog control with
a step resolution indicated by the position of the flashing JOG indicator. The output immediately
follows the setting, i.e. no OK is required. With the output on the right-hand display shows actual
current, not current limit (except in constant current mode). If JOG SET I is selected the JOG
indicator under the selected digit will flash at half speed ('lazy' flash). To observe the effect of
jogging the current limit it will be necessary to either turn the output off (so that the display
permanently shows the current limit) or to press VIEW V/I LIMITS which causes the current limit to
be displayed until 3 seconds after movement of the jog control ceases.

Instantaneous Current Output

The current limit control can be set to limit the continuous output current to levels down to 1mA (0·1
mA on 500mA range). However, in common with all precision bench power supplies, a capacitor is
connected across the output to maintain stability and good transient response. This capacitor
charges to the output voltage and short-circuiting of the output will produce a current pulse as the
capacitor discharges which is independent of the current limit setting.
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