AimTTi CPX400S User manual

CPX400S & SA & SP
PowerFlex DC Power Supply

1
Table of Contents
Specification 2
Safety 5
Installation 6
Connections 7
Manual Operation 10
Remote Analogue Control (CPX400SA only) 15
Remote Interface Operation (CPX400SP only) 19
Remote Commands (CPX400SP only) 29
Maintenance 34
Note: The latest revisions of this manual, device drivers and software tools can be
downloaded from: http://www.tti-test.com/go/csx
This manual is 48511-1520 Issue 8

2
Specification
General specifications apply for the temperature range 5°C to 40°C. Accuracy specifications apply
for the temperature range 18°C to 28°C after 1 hour warm-up with no load and calibration at 23°C.
Typical specifications are determined by design and are not guaranteed.
OUTPUT SPECIFICATION
Voltage Range:
0V to 60V
Current Range:
0A to 20A
Note: In manual operation, actual maxima for voltage and current are typically 1% greater that the figures
given above.
Power Range:
Up to 420W
Output Voltage Setting:
By coarse and fine controls.
Output Current Setting:
By single logarithmic control.
Operating Mode: By single logarithmic control.
Constant voltage (CV) or constant
current (CC) with automatic cross-
over, provided that the power
demanded stays with the power
envelope, see graph. Outside of
this envelope the output becomes
unregulated.
Operating Ranges: Four selectable ranges: 60V/20A, 60V/7A, 20V/20A and Custom Limits.
Any V/I setting of the 60V/7A or 20V/20A ranges always falls within the
appropriate part of the Power Envelope.
The 60V/20A range permits any setting up to 60V and 20A but the output will
become unregulated if operated outside of the Power Envelope, see above.
The voltage and current limits of the Custom Limits range can be set to any
Vmax between 0.1V & 60V and Imax between 0.01Aand 20A. This facility is
most useful in limiting operation to a particular part of the Power Envelope.
Settings Lock:
(S-Lock)
Voltage and current settings can be locked by a single button press.
Lock accuracy is equal to meter accuracy (see Meter Specification)
Output Switch:
Electronic. Preset voltage and current displayed when off.
Output Terminals: Front panel: Universal 4mm safety binding posts on 19mm (0·75”) pitch.
Rear Panel: Barrier strip connections
(CPX400SA/SP only)
Output Sensing: Switchable between local and remote. Remote connection by spring-loaded
push terminals on front panel and barrier strip on rear panel (CPX400SA /SP
only).
Output Protection: Forward protection by Over-Voltage Protection (OVP) and Over-Current
Protection (OCP) trips.
Reverse protection by diode clamp for reverse currents up to 3A.
OVP Range: 1V to 66V set by front panel screwdriver adjustment or via the remote
interfaces (CPX400SP only). Setting resolution: 100mV. Response time:
Typically 1ms. Maximum voltage that should be applied across the terminals is
70V.
OCP Range: Measure-and-compare over-current protection is implemented in firmware and
can only be set via the remote interface (CPX400SP only). Setting resolution:
10mA. Response time: typically 500ms.
For CPX400S/SA, OCP is fixed at 22A.
CPX400S/SA/SP
Power Envelope

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Over-temperature
Protection:
The output will be tripped off if a fault causes the internal temperature to rise
excessively.
Line Regulation: Change in output for a 10% line change:
Constant voltage: <0.01% of maximum output
Constant current: <0.01% of maximum output
Load Regulation: Change in output for any load change within PowerFlex envelope, remote
sense connected:
Constant voltage: <0.01% of maximum output
Constant current: <0.05% of maximum output
Ripple & Noise
(20MHz bandwidth):
5mVrms max; typically <3mVrms, <15mV pk-pk, at maximum load, CV mode.
Transient Load
Response: <250us to within 50mV of set level for a 5% to 95% load change.
Voltage Programming
Speed (CPX400SP only): Maximum time required for output to settle within 1% of its total excursion
(for resistive load). Excludes command processing time.
Range and Setting 90% Load No Load 90% Load No Load
60V 7A
20V 20A Up Up 8ms 8ms 8ms 8ms Down Down 80ms 10ms 1.5s 1.2s
Temperature Coefficient:
Typically <100ppm/°C
Status Indication: Output ON lamp.
Constant voltage mode lamp.
Constant current mode lamp.
Unregulated (power limit) lamp
Remote lamp (CPX400SP only)
LAN lamp (CPX400SP only)
Trip message on display.
METER SPECIFICATIONS
Meter Types:
Dual 4 digit meters with 10mm (0.39") LEDs. Reading rate 4Hz.
Meter Resolutions:
10mV, 10mA
Meter Accuracies: Voltage 0.1% of reading ± 2 digits
Current 0.3% of reading ± 2 digits
ANALOGUE REMOTE CONTROL (CPX400SA only)
Isolated inputs and non-isolated outputs to set voltage and current limit.
Isolated control input
scaling: Rear panel control inputs (CV and CC) permit external 0V to 5V or 0 to10V
signals (with respect to the common Return) to set 0 to 100% of rated output
voltage and current. Inputs are protected against excess input voltages up to
60V. Isolation rating with respect to the output is 300V max.
Control input accuracy: Voltage: 0.3% ±20mV. Input impedance 10kΩ.
Current: 0.5% ±50mA. Input impedance 10k
Ω
.
Control output scaling:
Set values of 0 to 100% of rated output voltage and current generate 0 to 5V
signals at the rear panel Vout and Iout outputs. Outputs are short-circuit
protected. These signals are referenced to the output control circuit and will
therefore be within ~1V of the positive output potential.

4
Control output accuracy: Voltage: 0.3% ±20mV
Current: 0.5% ±50mA.
Output impedance: 125
Ω.
Remote Off: Rear panel connections allow a switch closure to turn output off. Remote Off
is referenced to the output control circuit and will therefore be within ~1V of
the positive output potential.
DIGITAL INTERFACES (CPX400SP only)
Full digital remote control facilities are available through the RS232, USB, LAN and GPIB
interfaces.
Voltage Setting:
16-bit, Resolution 10mV, Accuracy ± (0·05% +10mV)
Current Setting:
16-bit, Resolution 1mA, Accuracy ± (0·3% + 0·005A)
RS232:
Standard 9-pin D-connector. Baud rate 9600.
GPIB:
Conforming with IEEE488.1 and IEEE488.2
USB:
Standard USB 2.0 hardware connection. Operates as a virtual COM port.
LAN:
Ethernet 100/10base-T hardware connection. 1.4 LXI Core 2011.
Remote Command
Processing Time:
Typically <25ms between receiving the command terminator for a step
voltage change at the instrument and the output voltage beginning to change.
GENERAL
AC Input: 110V – 240V AC ± 10%, 50/60Hz.
Installation Category II.
Power Consumption:
600VA max.
Operating Range:
+5ºC to +40ºC, 20% to 80% RH.
Storage Range:
−
40ºC to + 70ºC.
Environmental:
Indoor use at altitudes up to 2000m, Pollution Degree 2.
Safety:
Complies with EN61010-1.
EMC:
Complies with EN61326.
Size: 107mm x 130mm x 400mm (WxHxD) ¼-rack width x 3U height
(optional rack mounting kit available).
Weight: 4.25kg

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Safety
This power supply is a Safety Class I instrument according to IEC classification and has been
designed to meet the requirements of EN61010-1 (Safety Requirements for Electrical Equipment
for Measurement, Control and Laboratory Use). It is an Installation Category II instrument intended
for operation from a normal single phase supply.
This instrument has been tested in accordance with EN61010-1 and has been supplied in a safe
condition. This instruction manual contains some information and warnings which have to be
followed by the user to ensure safe operation and to retain the instrument in a safe condition.
This instrument has been designed for indoor use in a Pollution Degree 2 environment in the
temperature range 5°C to 40°C, 20% - 80% RH (non-condensing). It may occasionally be
subjected to temperatures between +5°C and –10°C without degradation of its safety. Do not
operate while condensation is present.
Use of this instrument in a manner not specified by these instructions may impair the safety
protection provided. Do not operate the instrument outside its rated supply voltages or
environmental range.
WARNING! THIS INSTRUMENT MUST BE EARTHED
Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.
When the instrument is connected to its supply, terminals may be live and opening the covers or
removal of parts (except those to which access can be gained by hand) is likely to expose live
parts. The apparatus shall be disconnected from all voltage sources before it is opened for any
adjustment, replacement, maintenance or repair. Capacitors inside the power supply may still be
charged even if the power supply has been disconnected from all voltage sources but will be safely
discharged about 10 minutes after switching off power.
Any adjustment, maintenance and repair of the opened instrument under voltage shall be avoided
as far as possible and, if inevitable, shall be carried out only by a skilled person who is aware of
the hazard involved.
If the instrument is clearly defective, has been subject to mechanical damage, excessive moisture
or chemical corrosion the safety protection may be impaired and the apparatus should be
withdrawn from use and returned for checking and repair.
Make sure that only fuses with the required rated current and of the specified type are used for
replacement. The use of makeshift fuses and the short-circuiting of fuse holders is prohibited.
Do not wet the instrument when cleaning it.
The following symbols are used on the instrument and in this manual:-
Caution - refer to the accompanying documentation, incorrect operation
may damage the instrument.
Earth (ground) terminal.
mains supply OFF.
l
mains supply ON.
alternating current (ac)
direct current (dc)

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Installation
Mains Operating Voltage
This instrument has a universal input range and will operate from a nominal 115V or 230V mains
supply without adjustment. Check that the local supply meets theAC Input requirement given in
the Specification.
Mains Lead
Connect the instrument to the AC supply using the mains lead provided. Should a mains plug be
required for a different mains outlet socket, a suitably rated and approved mains lead set should be
used which is fitted with the required wall plug and an IEC60320 C13 connector for the instrument
end. To determine the minimum current rating of the lead-set for the intended AC supply, refer to
the power rating information on the equipment or in the Specification.
WARNING! THIS INSTRUMENT MUST BE EARTHED.
Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited.
Ventilation
The power supply is cooled by an intelligent multi-speed fan which vents at the rear. Take care not
to restrict the air inlets at top, bottom and side panels or the exit at the rear. In rack-mounted
situations allow adequate space around the instrument and/or use a fan tray for forced cooling.
Mounting
This instrument is suitable both for bench use and rack mounting. It is delivered with feet for bench
mounting. The front feet include a tilt mechanism for optimal panel angle.
A rack kit for mounting one to four of these quarter-width 3U high units in a 19” rack is available
from the Manufacturers or their overseas agents.

7
Connections
Front Panel Connections
The load should be connected to the positive (red) and negative (black) terminals marked
OUTPUT. The OUTPUT terminals are rated at 30A.
Remote sense connections to the load, if required, are made from the positive (+) and
negative (−) SENSE terminals. Switch the LOCAL/REMOTE switch to REMOTE when remote
sensing is required. Switch back to LOCAL when remote sensing is not in use.
The terminal marked is connected to the chassis and safety earth ground.
Rear Panel Connections (CPX400SP & CPX400SA only)
CPX400SP CPX400SA

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Output Terminals
The output and sense terminals are duplicated on the rear panel terminal blocks and are marked
+O/P, −O/P, +S and −S. These connections are paralleled with their front panel equivalents.
Switch the LOCAL/REMOTE switch to REMOTE when remote sensing is required. When the rear
panel Output terminals are used, the use of remote sense is always recommended to ensure that
output regulation is maintained within specification; connections can be made to either the front or
the rear remote sense terminals but never to both pairs of terminals at the same time. Switch back
to LOCAL when remote sensing is not in use.
Analogue Remote Control (CPX400SA only)
Connections CV and CC provide analogue control of the Output Voltage and Current Limit
respectively when slide switches CV and CC are set to Remote. These inputs, and their common
return signal (RTN), are isolated from the output; the isolation rating with respect to the output is
300V max. The input scaling can be set independently, by intermal links, as 0 to 5 Volts (the factory
default) or 0 to 10 Volts for 0 to 100% of maximum output. Maximum permissible input is 60V. CV
and CC can be used independently or together.
Return slide switches CV and CC to Local when analogue remote control is not in use.
Analogue Out (CPX400SA only)
Connections VOUT and IOUT provide analogue outputs scaled to the set output voltage and set
current limit respectively. The scaling is fixed at 0 to 5 Volts for 0 to 100% of maximum output.
VOUT and IOUT are always present on the terminals, whether the instrument is under local or remote
control.
Warning! COM is referenced to the output control circuit and will be within ~1V of the
positive output potential. VOUT and IOUT are always present on the terminals.
Do not apply external voltages to these terminals.
Remote On/Off (CPX400SA only)
A switch closure or logic low between connections Rem Off and COMmon will turn off the output.
Warning! COM is referenced to the output control circuit and will be within ~1V of the
positive output potential.
Do not apply external voltages to these terminals.
RS232 (CPX400SP only)
9−pin female D−connector with pin connections as shown below. Can be connected to a standard
PC port using a fully wired 1:1 male-female cable without any cross-over connections.
Pin Name Description
1 RI Passively asserted (+V through 10kΩ)
2 TXD Transmitted data from instrument
3
RXD
Received data to instrument
4 CTS
5 GND Signal ground
6 RTS Passively asserted (+V through 10kΩ)
7 DSR No internal connection
8 DTR
9 CD No internal connection
Signal ground is connected to instrument ground.

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USB (CPX400SP only)
The USB port is connected to instrument ground. It conforms with USB 2.0 (Full Speed) and
accepts a standard USB cable. The Windows plug-and-play functions should automatically
recognise that the instrument has been connected. If the correct driver is not found, follow the
Windows on-screen prompts and install the required files from the CD supplied.
LAN (CPX400SP only)
The LAN interface is designed to meet 1.4 LXI ( Lan eXtensions for Instrumentation) core 2011.
Remote control using the LAN interface is possible using a TCP/IP Socket protocol. The
instrument also contains a basic Web server which provides information on the unit and allows it to
be configured. Since it is possible to misconfigure the LAN interface, making it impossible to
communicate with the instrument over LAN, a LAN Configuration Initialise (LCI) mechanism is
provided via a recessed switch on the rear panel (marked LAN RESET) to reset the unit to the
factory default.
Further details are given in the Remote Operation chapter. For more information on LXI standards
refer to www.lxistandard.org/home
GPIB (CPX400SP only)
The GPIB signal grounds are connected to the instrument ground. The implemented subsets are:
SH1 AH1 T6 TE0 L4 LE0 SR1 RL2 PP1 DC1 DT0 C0 E2
The GPIB address is set from the front panel.

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At power on, the factory default setting is for the output to be off. The
preset output volts and current will be determined by the present control
settings and shown in the display. The VIEW lamp is lit to indicate that it is
the preset values that are being displayed.All other settings will be the
same as they were at last power off.
PowerFlex range which limits the maximum
current at the set voltage to that determined
by the power envelope or 20A, whichever is
the lower, see Power Limit paragraph later in
this section.
ON
OUTPUT
Hold
to Set
Manual Operation
Switching On
The POWER switch is located at the bottom left of the front panel.
When the POWER switch is turned on the lower meter briefly indicates the instrument firmware
revision; on the CPX400SP this is followed by the interface firmware revision ( IF shows in the
upper meter) before the display shows Volts andAmps; the LAN lamp above the right hand output
meters will also light but will go off after ~30s if an operational LAN connection is not found, see
LAN Error paragraph in LAN Interface section.
The dc output state at power-on can be set to be ‘always off’ or ‘same as at last power-off’. The
setting can be changed as follows. With the VIEW key held down, press and hold down the
OUTPUT key; the display will first show the present setting for 1 second (OP OFF if the factory
default is still selected) before flashing the new setting for 2 seconds ( LASt Set in this
instance). After 2 seconds the new setting is shown continuously in the display and the change is
implemented; release the OUTPUT and VIEW keys. Repeating the procedure will change the
setting back to the previous state.
Setting Up the Output
With the POWER switch on ( l ) and the OUTPUT switch off the output voltage and current limit
can be accurately preset using the VOLTAGE and CURRENT controls; the upper meter shows the
set voltage and the lower meter shows the set maximum current.
When the OUTPUT switch is switched on, the OUTPUT ON lamp and the CV (constant voltage)
lamp light; the upper meter continues to show the set voltage but the lower meter now shows the
actual load current.
Range Selection & Custom Limits
There are 4 possible ranges, selected by the keys immediately below the display; the associated
lamp lights to show which range is selected. Because changing ranges can change the output
voltage, range changing is only allowed if the output is off. If attempts are made to change range
with the output on, the display will briefly show the message turn oFF and the output lamp will
flash to prompt the user to turn the output off. The factory default range selection is the 60V/20A
The 60V/7A and 20V/20A ranges operate conventionally such that Constant Voltage (CV)
operation is possible over the full voltage range, provided that the load current is below the range
maximum; operation is always within the power envelope of the instrument. The VOLTAGE and
CURRENT controls are always scaled to set the range maximum when fully clockwise.
The CUSTOM LIMITS capability allows the maximum values of both the VOLTAGE and CURRENT
controls to be redefined by the user such that the controls operate over specific, lower, ranges.
This not only has the advantage of protecting against the accidental application of, for example,
excess voltages to the load, but also provides higher resolution analogue control over the specified
ranges using the full 300º rotation of the controls.
To set new CUSTOM LIMITS turn the output off and select the 60V/20A range; preset limits are
shown in the display. Use the MAIN and FINE VOLTAGE controls and the CURRENT control to set,

11
precisely, the new custom limits required. Press and hold the CUSTOM LIMITS key; the displays
flash the new limits for ~2s, after which the lower (A) display shows SEt to indicate that the new
limits have been stored. Release the key; the displays now show the preset V and I limits
corresponding to the knob settings within the newly defined ranges.
If the new limits fall outside the power envelope (see Power Limit paragraph below), such that
operation could change from CV or CC (Constant Current) to UNREGulated (power limit) under
certain load conditions, the CUSTOM LIMITS lamp will flash during the setting process to indicate
this and will continue to do so until the range key is released. If the lamp is constantly on during
setting this indicates that VMAX x IMAX <420W and that operation should therefore generally stay in
CV or CC mode. CUSTOM LIMITS remains selected until another range key is pressed.
Reselecting CUSTOM LIMITS with a short key press recalls the same custom limits as last set.
When CUSTOM LIMITS is selected, the limit of the MAIN VOLTAGE control is exactly as set by the
above procedure when the FINE control is set at its mid-point, marked on the panel with a
•
. The
FINE control itself can be usefully used to give an additional fine adjustment of ±1% (of the range
maximum).
Constant Voltage
The output voltage is adjusted using the MAIN and FINE VOLTAGE controls; the CURRENT control
sets the maximum current that can be supplied.
The CV lamp lights to show constant voltage mode.
Constant Current
If the load resistance is low enough such that, at the output voltage set, a current greater than the
current limit setting would flow, the power supply will automatically move into constant current
operation. The current output is adjusted by the CURRENT control and the VOLTAGE controls set
the maximum voltage that can be generated.
The CC lamp lights to show constant current mode.
Instantaneous Current Output
The current limit control can be set to limit the continuous output current to levels down to 10mA.
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.
Power Limit
The maximum current at different voltage settings is limited by the power envelope illustrated
below:
CPX 400S/SA/SP
Power Envelope

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The power envelope is set to give 60V/7A, 42V/10A and 20V / 20A under all supply conditions
(both outputs loaded); at lower output voltages the output power is restricted by the 20A current
maximum.
When the power limit is exceeded, the status indication will change from CV or CC to UNREG. For
example, if the supply is set to 20V, with the current limit at maximum, and is connected to a 2Ω
load, 10 Amps will flow and the supply will be in CV mode. As the voltage across the load is
increased, the power into the load increases until, at about 29V, the power limit is exceeded and
the supply changes from CV to UNREG.
Connection to the Load
The load should be connected to the positive (red) and negative (black) front panel OUTPUT
terminals. Both are fully floating and either can be connected to ground. Alternatively, on the
CPX400SA/SP, connection can be made to the duplicate rear panel Output terminals, appropriate
for when the instrument is used in a rack.
When the rear panel Output terminals are used, the use of remote sense is always recommended
to ensure that output regulation is maintained within specification, see Remote Sensing section
below. If the rear panel Output terminals are used without remote sense make sure that the front
panel switch is set to LOCAL. Regulation will be degraded a little when local sense is used
because of the additional small voltage drop in the internal wiring to the rear terminals.
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 5mΩconnecting leads will drop 0.2V at
20 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 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. 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). Instability and poor regulation caused by noise on the sense leads when
connected to complex loads can be minimised by fitting a suitable capacitor directly between each
Sense terminal and its associated Output terminal at the PSU front panel. A polyester or low ESR
electrolytic with a value between 10uF and 100uF will generally be adequate.
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.
When the rear panel Output terminals are used on the CPX400SA/SP, the use of remote sense is
always recommended to ensure that output regulation is maintained within specification;
connections can be made to either the front or the rear remote sense terminals but never to both
pairs of terminals at the same time. Connect the Sense terminals to the load, following the
guidelines above, and set the LOCAL/REMOTE switch to REMOTE.
Series or Parallel connection with other units
The output of the power supply is 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 ( ) is 300VDC.
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.

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Overvoltage protection (OVP) is fully variable within the range 1V to 66V. For
CPX400S and CPX400SP in Local mode the OVP limit is set via the screwdriver
adjustable OVP preset potentiometer, accessible through a hole in the front panel
immediately above the OVP key. Rotating the preset clockwise increases the limit,
which can be read directly on the user display by pressing the OVP key beneath the
preset. When in remote control mode (CPX400SP only) an independent OVP value
is used which is set via the RS232, USB, LAN (LXI) or GPIB interfaces (default value
66V); see the Remote Command section for further details. If the voltage on the
output exceeds the set OVP for any reason, including an externally forced voltage,
the output will be tripped off.
It should be noted that the unit can only source current and cannot sink it, thus units cannot be
series connected in anti-phase.
The unit can be connected in parallel with others to produce higher currents. Where several units
are connected in parallel, the output voltage will be equal to that of the unit with the highest output
voltage setting until the current drawn exceeds its current limit setting, upon which the output will
fall to that of the next highest setting, and so on. In constant current mode, units can be connected
in parallel to provide a current equal to the sum of the current limit settings. For optimum operation
connect the power supplies separately to the load.
Note that the output terminals are rated at 30Amaximum; if two or more outputs are operated in
parallel to source higher currents than this the junction should be made at a separate point, not
one of the terminals.
Protection
OVP
Over-current protection (OCP) is implemented in firmware and can only be set and used when
under remote control via the RS232, USB, LAN (LXI) or GPIB interfaces (CPX400SP only).
Setting resolution is 10mA and typical response times are 500ms. In local mode, and for
CPX400S/SA, OCP is still active but automatically defaults to 22 Amps.
When the output is tripped the displays will show OUP triP . and the OUTPUT lamp will flash.
Turn the output off; the trip message should be replaced with the normal preset V and I readings.
When the cause of the trip has been removed the output can be switched on again.
Even with the output off the load is still connected to the power supply output stage. Do not apply
external voltages in excess of 70V to the power supply terminals or damage may result.
The output is protected from reverse voltages by a diode; the continuous reverse current must not
exceed 3 Amps, although transients can be much higher.
Over-temperature Protection
A sensor on the secondary heatsink will detect over-temperature due to blocked air-flow, fan failure
or other circuit fault. Over-temperature will turn the output off, the OUTPUT indicator will flash, and
the display will show the message OtP trip.The output will remain shut down even after the
heatsink has cooled down. When the cause of the over-temperature has been removed and the
heatsink has cooled to normal working temperatures the output can be reset by turning the
POWER switch to off (
), then on ( I ) again.
View Settings
Lock Settings
Pressing the LOCK key digitally locks the set voltage and current limit. The settings are stored with
a precision of better than 1 digit. Subsequent adjustments of the VOLTAGE and CURRENT
controls will have no effect.
The set voltage and current limit are always shown when the
output is off but can also be viewed when the output is on by
pressing the VIEW key; the VIEW lamp is lit whilst the VIEW key
is pressed.

14
Because cancelling LOCK will cause the output settings to change if the VOLTAGE and CURRENT
control positions have been moved, warning reminders are given before LOCK is cancelled. Press
and hold the key to cancel LOCK.
If the OUTPUT is off (the safe condition) the display will flash the ‘unlocked’ settings twice before
the change is implemented; the LOCK lamp goes off.
Releasing the LOCK key at any time while the display is flashing will abort the LOCK cancellation.
Attempting to select a different range with LOCK enabled is not allowed; if attempted, the message
Unloc is shown briefly in the display and the LOCK lamp is also flashed. If the output is also on
when these actions are attempted the message turn oFF is first shown in the display
(accompanied by the output lamp flashing) followed by the message Unloc (with the LOCK
lamp flashing).
The LOCK status at power on is the same as at last power off.
If the output is still on, OP on (output on) will flash twice in the
display, followed by flashing of the new ‘unlocked’ settings for 2-3
seconds (slowly at first, then faster) before the change is finally
implemented; the LOCK lamp goes off when the change is made.

15
Remote Analogue Control (CPX400SA only)
Remote analogue control of output voltage and current is possible using variable external control
voltages applied between the rear panel CV or CC and Return (RTN) inputs respectively. These
inputs are isolated from the output; the isolation rating with respect to the output is 300V max.
Inputs are protected against excess input voltages of up to 60V.
The Analogue Out control voltages Vout and Iout of one unit acting as a ‘master’ can be used to
control a ‘slave’ unit via the slave’s CV and CC inputs respectively.
Analogue Voltage Control
Remote analogue voltage control is achieved by setting the rear panel CV switch to Remote and
applying a programming voltage between the inputs CV and RTN.
The front panel VOLTAGE controls and voltage range selection are disabled when Remote is set
on the CV switch. Set the switch to Local to return control to the front panel.
The default input voltage scaling is 0V to 5V for 0 to 100% of the maximum output voltage. The
input voltage scaling can be changed to be 0V to 10V by changing an internal shorting link.
Disconnect the instrument from the AC source and remove the cover as follows. Remove the two
plastic push-rivets at each side edge of the top cover. Use the blade of a small screwdriver to first
ease out the rivet head and then fully remove the rivet body. Remove the three rear panel screws
securing the top cover; slide the cover back and lift off.
Referring to the top view of the instrument shown in the drawing, move the tall shorting link in
position LK1 to link centre and '10V' pins instead of centre and '5V' pins.
Remote CV can be used with either Local or Remote CC.
Analogue Current Control
Remote analogue constant current control is achieved by setting the rear panel CC switch to
Remote and applying a programming voltage between the inputs CC and RTN.
The front panel CURRENT control and current range selection are disabled when Remote is set on
the CC switch. Set the switch to Local to return control to the front panel.

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The default input voltage scaling is 0V to 5V for 0 to 100% of the maximum output current. The
input voltage scaling can be changed to be 0V to 10V by changing an internal shorting link.
Disconnect the instrument from the AC source and remove the cover as follows.
Remove the plastic push-rivets at each side edge of the top cover. Unse the blade of a small
screwdriver to first ease out the rivet head and then fully remove the rivet body. Remove the three
rear panel screws securing the top cover; slide the cover back and lift off.
Referring to the top view of the instrument shown in the drawing, move the tall shorting link in
position LK3 to link centre and '10V' pins instead of centre and '5V' pins.
Remote CC can be used with either Local or Remote CV.
CAUTION. Do not apply external control voltages to either the CV or CC input that exceed
the maximum for the set input range (5V or 10V). The inputs are protected against excess
voltages but the instrument will attempt to supply an output voltage or current in excess of its
maximum rating if the control voltage exceeds its range limit, with possible consequential
damage.
Practical Considerations when using CV and CC
The stability of the control voltages directly affects the stability of the output. Any noise on the
control signals will generate noise on the output. To minimise noise on the output connect the
control voltages to the CV, CC and RTN inputs using twisted or screened pairs (screens grounded
at one end only) and keep the connections as short as possible. Note that output noise is
inherently slightly higher when analogue remote control is used because of intrinsic noise in the
isolating input circuitry, see the Specification.
The diagrams below show the connections for Constant Voltage (CV) and Constant Current (CC)
control using an external voltage.
Constant Voltage Control Constant Current Control
Note that when the OUTPUT is on, the instrument’s display always shows the actual output voltage
and current, whichever control source is active. However, when the OUTPUT is off, the display will
show the preset voltage and current set by the front panel controls (or the digital interface if active)
and not the values determined by the CV and CC inputs even if they have been made active (CV
and CC set to Remote). To avoid confusion it is good practice to set the front panel controls to
minimum when remote CV and CC are used.

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Analogue Out Control Voltages
Analogue Out control voltages Vout and Iout are generated from the actual internal control voltages,
for which the active source can be the front panel controls, or the remote analogue inputs CV and
CC. Vout and Iout are scaled such that 0 to 100% of the maximum output voltage and current
generate 0V to 5V at the rear panel Vout and Iout terminals with respect to COM. Iout always
corresponds to the set current, whether the output is on or off, but Vout goes to 0V when the output
is off.
Warning! COM is referenced to the output control circuit and will be within ~1V of the
positive output potential. VOUT and IOUT are always present on the terminals.
Parallel Operation in Master-Slave Configuration
Parallel operation in Master-Slave configuration permits higher output currents to be realised with
equal current sharing between units and control of both voltage and current from a single unit. The
diagram shows 3 units connected in parallel. For equal current sharing each unit must be
independently connected to the load with pairs of wires of equal gauge and length to ensure equal
voltage drops. Connect the Vout , Iout and COM of the master to the CV, CC and RTN inputs of the
slaves (set CV and CC switches to Remote) as shown.
Parallel Operation in Master-Slave Configuration
Notes:
1. Units can be wired for CV (constant
voltage), CC (constant current) or both
(both shown). Set CV and/or CC
switches of slaves to Remote.
2. Connect outputs in parallel using equal
length wires to the load.
3. If remote sensing is required use only
remote sense from the master to the
load.
4. For constant current operation set the
required voltage overhead on the
master.

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The voltage and current of the master can be set by either the front panel controls, via the digital
interface, or by an external voltage applied to its own CV and CC analogue control inputs.
In constant voltage mode the voltage across the load is that set on the master unit by its front
panel controls, via the digital interface or by the analogue CV remote control input. The current
limit for the system (i.e. the current in constant current mode) is the current limit set on the master
x n, where n is the total number of units connected in parallel.
Isolated or Series Operation in Master-Slave Configuration
Isolated or Series operation in Master-Slave configuration permits tracking output voltages and
current limits to be set for multiple units from a single instrument. The diagram shows 2 units
connected in series for tracking ±Volts and tracking current limits. Connect the Vout , Iout and COM
of the master to the CV, CC and RTN inputs of the slaves (set CV and CC switches to Remote) as shown.
The diagram shows remote sense connections to the load; set the front panel sense switch to Remote.
If remote sensing is not required, do not use the sense wires and set the sense switch to Local.
If independent current limits are required set CC to Local and set the limits from the front panel of
each unit.
Warning! In series operation take care not to exceed the maximum rated operating voltage
(300V) of any terminal with respect to earth ground ( ).
Remote Off
A switch closure or logic low between the rear panel Rem Off and COM inputs will remotely turn
off the output if it was previously on; the front panel OUTPUT lamp will also go off. Opening the
switch between Rem Off and COM will turn the output on again.
Warning! COM is referenced to the output control circuit and will be within ~1V of the
positive output potential.

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Remote Interface Operation (CPX400SP only)
The instrument can be remotely controlled via its RS232, USB, LAN or GPIB interfaces.
USB remote control operates in a similar way to RS232 but via the USB connector. Software
supplied with the instrument sets up the controlling computer to treat the USB connection as a
virtual COM port. Application software on the computer can then access the instrument via that
COM port.
The LAN interface is designed to meet 1.4 LXI ( Lan eXtensions for Instrumentation) Core 2011.
Remote control using the LAN interface is possible using the TCP/IP Sockets protocol. The
instrument also contains a basic Web server which provides information on the unit and allows it to
be configured from a web browser. Simple command line control from the browser is also
possible.
All interfaces are, by default, live at all times (a LXI requirement) but access to individual interfaces
may be restricted using the configuration options on the web pages.
Interface Locking
All the remote interfaces are live at all times, to remove any need to select the active interface and
to ensure that the LAN interface is always available (as demanded by the LXI standard). To reduce
the risk of the instrument being inadvertently under the control of two interfaces at once a simple
lock and release mechanism is provided in the instruction set. The lock is automatically released
where it is possible to detect disconnection and when the local button is pressed. Access to the
interfaces may also be restricted using the web pages.
Any interface may request to have exclusive control of the instrument by sending an “IFLOCK”
command. The lock may only be released by sending an “IFUNLOCK” command from the interface
instance that currently has the lock and may be queried from any interface by sending an
“IFLOCK?” command. The reply to any of these commands will be “-1” if the lock is owned by
another interface instance, “0” if the interface is free and “1” if the lock is owned by the requesting
interface instance. Sending any command from an interface without control privileges that
attempts to change the instrument status will set bit 4 of the Standard Event Status Register and
put 200 into the Execution Error Register to indicate that there are not sufficient privileges for the
required action.
Note: it is also possible to configure the privileges for a particular interface to either ‘read only’ or
‘no access’ from the Web page interface.
Address Selection
The instrument address capability is strictly required only by the GPIB interface. However, use can
be made of theADDRESS? command over any of the interfaces to easily identify which instrument
is being controlled by a particular COM port (for RS232 or USB) or TCP socket (for LAN). Note
that the LAN interface also has a separate ‘Identify’ function, accessible from the instrument’s web
pages, that flashes the instrument’s display until the function is cancelled.
The address is set from the instrument’s front panel as follows. Start with the instrument off and,
with the VIEW and LOCK keys both held down, switch the instrument on. The display will show
Addr in the Volts display and nn in the Amps display where nn is the present setting (default
Addr 11 ). The address can be decremented and incremented by the VIEW and LOCK keys
respectively in the range 1 to 31 inclusive (not 0), with 'wrap-round'. The address is confirmed and
the process exited by holding down the OVP key; the display will show SEt and the new address
for approximately 2 seconds, returning to the normal Volts andAmps display when the new
address has been accepted.
The address can also be set from the instrument’s web pages.