Thurlby Thandar Instruments New PL Serie Manual Del Usuario página 11

Instantaneous Current Output
The current limit control can be set to limit the continuous output current to levels down to 1mA
(0.1mA 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 loading of the output will produce a current pulse as
the capacitor discharges which is independent of the current limit setting.
Current Meter Averaging
Efficiency
The power supply minimises dissipation by using electronic line frequency pre-regulation to
maintain a low overhead voltage to the output regulators. In addition, to optimise operation at
extremes of line input voltage and DC output power, the transformer secondary is intelligently tap-
changed by a relay. Hysteresis is used at the threshold point to prevent unnecessary switching
when the output is set at about that level. Apart from an audible 'click' the user will be unaware
that the relay has switched; there will be no disturbance on the output.
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 unit has a very low output impedance, but this is inevitably increased by the resistance of the
connecting leads. At higher 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).
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 cables (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.
Switch the LOCAL/REMOTE switch back to LOCAL when remote sensing is not in use.
Series or Parallel Connection with Other Outputs
The outputs of the power supply are fully floating and may be used in series with other power
supply units to generate high DC voltages up to 300V DC.
The maximum permissible voltage between any terminal and earth ground (
WARNING! Such voltages are exceedingly hazardous and great care should be taken to shield
the output terminals for such use. On no account should the output terminals be touched when
the unit is switched on under such use. All connections to the terminals must be made with the
power switched off on all units.
It should be noted that the unit can only source current and cannot sink it, thus units cannot be
series connected in anti-phase.
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To reduce the measurement jitter with rapidly varying load
currents a 2-second time constant can be selected by pressing the
METER AVERAGE key; the indicator beside the key lights when
meter averaging is selected. Press the key again to CANCEL
meter averaging and return to the standard 20ms time constant.
This problem can be minimised by using short, thick, connecting
leads, but where necessary it can be completely overcome by
using the remote sense facility.
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 SENSE terminals and connect directly to the load. Switch
the LOCAL/REMOTE switch to REMOTE.
) is 300VDC