16
Range Selection
The instrument has three ranges: 35V/3A, 15V/5A and 35V/500mA (QL355) or 56V/2A, 25V/4A
and 56V/500mA (QL564). The selected range is shown by an illuminated indicator below the
appropriate legend at the top right-hand side of the instrument; when the 500mA range is
selected the indicator legend is mA to emphasise that the current meter now shows milliamps not
amps.
To change range press SHIFT followed by
RANGE or RANGE
; each press of
RANGE
selects the next range to the left; each press of RANGE
selects the next range to the right;
there is no 'wrap-round'. When the range is changed the indicator that represents the new range
and the OK key both flash; pressing OK sets the new range. To exit without changing range
press ESCAPE. Pressing any other key whilst in range change mode causes the warning buzzer
to beep twice; no other action is taken. If OK is not pressed within 10 seconds of the last range
change key press the range selection remains unchanged.
The range can only be changed when the output is off. Pressing the
RANGE or RANGE
keys with the output on will cause the output ON/OFF key (as well as the OK key) to flash. The
output may be turned off with the ON/OFF key and the range then changed by pressing OK, or
OK may be pressed directly in which case the output is automatically turned off and the range
then changed.
If a range change causes a voltage or current limit setting to exceed the corresponding maximum
of the new range the range change is accepted but the setting is made equal to the maximum of
the new range.
Note that the OVP setting is not changed when the range is changed (e.g., for QL355, an OVP
setting of 38V remains valid on the 15V range); it is left to the user to independently change the
OVP setting if required.
Output Settings – Front Panel Lock
To avoid accidental changes to the output settings in a bench or rack set-up, front panel control
of Range, Voltage, Current Limit, OVP and OCP can be ‘locked’ and ‘unlocked’ with alternate
uses of the #33 function, see Extra Functions section. The output ON/OFF key remains
unlocked, as does selection of remote sense. Front panel lock still operates in remote control
mode (P models only) but is ignored by the remote commands.
On triple output models the AUX output voltage is also locked when Output 1 settings are locked
but, additionally, the
CONTROL
keys remain unlocked. All outputs are locked and unlocked
together if #33 is used in Link mode, see Auxiliary Output and Main Outputs-Link Mode sections.
Connection to the Load
The load should be connected to the positive (red) and negative (black) OUTPUT terminals.
Both are fully floating and either can be connected to ground.
Remote Sensing
The instrument has a very low output impedance, but this is inevitably increased by the
resistance of the connecting leads. At high currents this can result in significant differences
between the indicated source voltage and the actual load voltage (two 20m
Ω
connecting leads
will drop 0·2V at 5 Amps, for instance). This problem can be minimised by using short, thick,
connecting leads, but where necessary it can be completely overcome by using the remote sense
capability. This requires the sense terminals to be connected to the output at the load instead of
at the source; insert wires into the spring-loaded REMOTE SENSE terminals and connect directly
to the load.
Select remote sense by pressing SHIFT, SENSE; the OK key flashes and the lamp above the
remote sense terminals lights to show that remote sense will be selected when OK is pressed.
Press OK to confirm; press ESCAPE to exit without changing state. Remote sense is turned off
by pressing SHIFT, SENSE again; the OK key flashes and the remote sense lamp goes off to
indicate that local sense will be restored when OK is pressed. Press OK to confirm; press
ESCAPE to exit without changing state.
