Range Selection; Connection To The Load; Remote Sensing - TTI QL Serie Manual De Instrucciones

Range Selection

The instrument has three ranges: 35V/3A, 15V/5A and 35V/500mA (QL355); 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. 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.

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 20mΩ 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.
To avoid instability and transient response problems, care must be taken to ensure good coupling
between each output and sense lead. This can be done either by twisting the leads together or by
using coaxially screened cable (sense through the inner). An electrolytic capacitor directly across the
load connection point may also be beneficial.
The voltage drop in each output lead must not exceed 0·5 Volts.
The QL355P/QL564P has rear panel output and sense terminals, appropriate for when the
instrument is used in a rack. The rear panel sense terminals should always be used with the rear
panel output connections.
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