Aim TTi LDH400P User guide
LDH400P
400W DC Electronic Loads
INSTRUCTION MANUAL
Contents
1. Introduction ................................................................................................... 4
2. Specification ................................................................................................. 5
3. Safety ............................................................................................................ 9
4. Installation ...................................................................................................10
4.1 Mains Operating Voltage .................................................................................................. 10
4.2 Mains Lead ....................................................................................................................... 10
4.3 Mounting ........................................................................................................................... 10
4.4 Ventilation ......................................................................................................................... 10
4.5 Fuses ............................................................................................................................... 11
5. Connections ..................................................................................................12
5.1 Front Panel Connections .................................................................................................. 12
5.2 Rear Panel Connections ................................................................................................... 12
5.3 Prospective Fault Current Protection ................................................................................ 13
6. Initial Operation ...........................................................................................14
6.1 Organisation of this manual .............................................................................................. 14
6.2 Load modes ...................................................................................................................... 14
6.3 Constant and Transient Operation .................................................................................... 14
6.4 Dropout voltage ................................................................................................................ 14
6.5 Slow Start ......................................................................................................................... 14
6.6 Voltage and Current Limit Conditions ............................................................................... 15
6.7 Power Limit ....................................................................................................................... 15
6.8 Input Condition Lamps ...................................................................................................... 15
6.9 Fault Conditions ................................................................................................................ 15
6.10 Connecting the Load to the Source .................................................................................. 16
6.11 Switching On .................................................................................................................... 16
7. Front Panel Operation ..................................................................................17
7.1 Keys and ∆ Adjust ............................................................................................................. 17
7.2 The Display and the Home Screen ................................................................................... 18
7.3 General Numeric Entry of Parameters .............................................................................. 20
7.4 Variation of Parameter Values using ∆ Adjust ................................................................... 20
7.5 Configuring the Load ........................................................................................................ 20
7.6 Selection of Load Mode .................................................................................................... 21
7.7 Level A and Level B Setting .............................................................................................. 21
7.8 Dropout Voltage ................................................................................................................ 21
7.9 Slow Start ......................................................................................................................... 22
7.10 Introduction to Transient Operation .................................................................................. 22
7.11 Transient Menu ................................................................................................................. 22
7.12 Transient Frequency ......................................................................................................... 23
7.13 Transient Duty Cycle ........................................................................................................ 23
7.14 Slew Rate ......................................................................................................................... 23
7.15 Voltage and Current Limits ............................................................................................... 24
7.16 Store and Recall Facilities ................................................................................................ 25
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7.17 Utilities Menu .................................................................................................................... 26
8. Analogue Remote Control ........................................................................... 27
8.1 Remote Voltage Control ................................................................................................... 27
8.2 Remote Level Select ........................................................................................................ 27
9. Application Notes ........................................................................................ 28
9.1 Sources ............................................................................................................................ 28
9.2 Stability of Source and Load Combinations ...................................................................... 29
9.3 Dynamic Behaviour in Transient Operation ...................................................................... 29
9.4 Start-up transients ............................................................................................................ 30
9.5 Characteristics of each Operat ing Mode .......................................................................... 30
9.6 Multiple Unit Operation ..................................................................................................... 32
10. Remote Interface Configuration .................................................................. 33
10.1 GPIB Interface .................................................................................................................. 33
10.2 RS232 Interface ............................................................................................................... 33
10.3 USB Interface and Device Driver Installation .................................................................... 34
10.4 LAN Interface ................................................................................................................... 34
10.5 Interface Locking .............................................................................................................. 36
11. Status Reporting .......................................................................................... 37
11.1 Input State and Input Trip Registers (ISR & ISE and ITR & ITE). ..................................... 37
11.2 Standard Event Status Registers (ESR and ESE) ............................................................ 38
11.3 Execution Error Register (EER) ........................................................................................ 39
11.4 Status Byte Register (STB) and GPIB Service Request Enable Register (SRE) .............. 39
11.5 GPIB Parallel Poll (PRE) .................................................................................................. 40
11.6 Query Error Register - GPI B I EEE Std. 488.2 Error Handling ........................................... 40
11.7 Power on Settings ............................................................................................................ 40
11.8 LDH400P Status Model .................................................................................................... 41
11.9 Register Summary ............................................................................................................ 41
12. Remote Commands ...................................................................................... 42
12.1 Remote and Local Operation ............................................................................................ 42
12.2 Remote Command Handling ............................................................................................ 42
12.3 Remote Command Formats ............................................................................................. 42
12.4 Command Timing ............................................................................................................. 43
12.5 Response Formats ........................................................................................................... 43
12.6 Command List .................................................................................................................. 43
13. Maintenance ................................................................................................ 47
13.1 Cleaning ........................................................................................................................... 47
13.2 Fuses ............................................................................................................................... 47
13.3 Calibration ........................................................................................................................ 47
13.4 Firmware Update .............................................................................................................. 47
13.5 Troubleshooting ................................................................................................................ 47
2
Full operating and programming instructions for this instrument can be found in the appropriate
product folder of the accompanying CD-ROM.
This information can also be downloaded from t he suppor t page of the Aim-TTi website,
http://www.aimtti.com/support
.
This manual is 48511-1830 Issue 1
Français
14. Sécurité ........................................................................................................48
Les instructions complètes de fonct ionnement et de programmation de cet instrument se
trouvent dans le dossier approprié du CD-ROM d’accompagnement.
Ces informations sont également t éléchar geables depuis la page de support du site Internet de
Aim-TTi, http://www.aimtti.com/support
.
Numéro du manuel 48511-1830, 1 édition.
Deutsch
15. Sicherheit .....................................................................................................49
Vollständige Betriebs- und Programmieranweisungen für dieses G er ät finden Sie im
entsprechenden Produktordner der beigefügten CD-ROM.
Diese Informationen können auch von der Support-Seite auf der Aim-TTi-Website
heruntergeladen werden, http://www.aimtti.com/support
Italiano
16. Sicurezza ......................................................................................................50
Le istruzioni complete per il funzionamento e la programm azione dello strum ent o sono
incluse nella relativa cartella del prodotto del CD-ROM fornito.
È anche possibile scaricare queste informazioni dalla pagina dell’assistenza del sito Web
Aim-TTi, http://www.aimtti.com/support
Questomanuale è la versione 48511-1830 revisione 1.
Español
17. Seguridad .....................................................................................................51
Las instrucciones completas de funcionamiento y prog r am ación de este instrumento
pueden encontrarse en la carpeta del producto correspondiente en el CD-ROM adjunto.
También es posible descargar esta información desde la página de asistencia de la web
de Aim-TTi, http://www.aimtti.com/support
.
Este manual es el 48511-1830 versión 1.
3
1. Introduction
This DC electronic load is for use in investig at ing the behaviour of many different types of high
voltage DC power sources such as PFCs, batteries, solar cells, fuel cells or wind generators, as
well as electronic power supply units.
The load inputs are rated to CAT II (300V). This allows for PFCs and mains connected power
supplies to be directly tested using the electronic load without t he need for an isolation
transformer.
The unit provides four different operating modes: constant current, constant power, constant
resistance and constant conductance.
It operates over the voltage range 10 to 500 Volts and the current range 0 to 16 Amps with a
continuous power dissipation capability of up to 400 Watts.
A low voltage dropout facility is provided to protect sources such as bat t eries from damaging
levels of discharge by reducing the load current when the source voltage falls below the dropout
threshold setting.
An internal transient generator can r epeat edly switch the load between two different oper at ing
levels, level A and level B. The frequency and duty cycle of the transients can be set over a wide
range. The transients can also be initiated by an external logic signal. The transitions between
the levels have a true linear slewing characteristic in all modes, with the slew-rate being
adjustable over a wide range.
The unit meters and displays measured values of Volts & Amps and equivalent Watts & Ohms. A
monitor output providing a voltage proportional to the cur r ent flowing allows the behaviour of a
source to be viewed on an oscilloscope or external meter.
All adjustable system parameters can be set via numeric keyboard entry or via the dig ital rem ot e
interfaces for quick and convenient instrument control.
Up to 30 non-volatile storage locations can be used to store and recall instrument parameter set
ups, ideal for test and calibration procedures.
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An external control voltage can also be used to set the level of the load. Any desired waveform
can be applied, with the internal slew rate control circuit remaining active to provide additional
control.
The unit is fully protected against excessive current , power dissipation or internal t em per ature,
and minimises audible noise by automatically controlling the fan speed according t o t he power
dissipation.
Current:
16 Amps max. through the front and rear panel terminals.
Voltage:
500 Volts max. while conducting current.
Power:
400 Watts max. up to 28ºC, derating t o 360 watts at 40º C.
Minimum Operating Voltage:
10V.
resistance:
1180kΩ to load negative).
Reverse Polarity:
Body diode will conduct; 16 Amps max.
Isolation Voltage:
CAT II (300V) either load input to chassis ground.
Rear Panel Input:
Safety terminals accepting 4mm plugs at 16 Amps max.
Front Panel Input:
Safety terminals accepting 4mm plugs at 16 Amps max.
Current Range:
0 to 16 A (1 mA resolution).
Setting Accuracy:
± 0·2% ± 30 mA.
Regulation:
< 30 mA for 90% load power change (V > 25 Volts).
Temperature Coefficient:
< (±0·02% ± 5 mA) per ºC.
Slew Rate Range:
5 Amp per s to 500 Amp per ms.
Minimum transition time:
50 µs.
Power Range:
0 to 400 Watts (100 mW resolution).
Setting Accuracy:
± 0·5% ± 2 W ± 30 mA (V > 25 Volts).
Regulation:
< 2% over 25 V to 550 V source voltage change.
Temperature Coefficient:
< (± 0·1% ± 5 mA) per ºC.
Slew Rate Range:
60 W per s t o 6000 W per ms.
Minimum transition time:
150 µs.
Resistance Range:
50 Ω to 10 kΩ (1 Ω resolution).
Setting Accuracy:
±0·5% ± 2 digits ± 30 mA (V > 25 Volts).
Regulation:
< 2% for 90% load power change (V > 25 Volts).
Temperature Coefficient:
< (±0·04% ± 5 mA) per ºC.
Slew Rate Range:
1 Ω per ms to 100 Ω per µs.
Minimum transition time:
150 µs.
2. Specification
Accuracy specifications apply for 18°C – 28ºC, using the rear panel terminals, after 30 minutes
operation at the set conditions. Setting ac cur ac ies apply with slew rate at the ‘Default ’ setting.
INPUT
Maximum Input Ratings
Minimum effective
Off State Leakage:
Input Terminals
OPERATING MODES
Constant Current Mode (CC)
(1)
(2)
1Ω .
<5 mA (including voltage sense circuit input resistance - typically
Constant Power Mode (CP)
(1)
(2)
Constant Resistance Mode (CR)
(1)
(2)
5
Conductance Range:
0·001 to 1 A/V (1 mA/V resolution)
Setting Accuracy:
± 0·5% ± 2 digits ± 30 mA (V > 25 Volts).
Regulation:
< 2% for 90% load power change (V > 25 Volts).
Temperature Coefficient:
< (±0·04% ± 5 mA) per ºC.
Slew Rate Range:
0·1 A/V per s to 10 A/V per ms.
Minimum transition time:
150 µs.
Pulse Repetition Rate:
Adjustable from 0·01Hz (100 seconds) to 10k Hz.
Pulse Duty Cycle:
1% to 99% (percentage of period at Level A).
Setting Accuracy:
±1 %
Setting Accuracy:
± 10% (on linear part of slope, excluding high frequency aberrations).
Variation in Level Settings:
± 5 digits of specified setting resolution for present mode and range.
internal transient generator.
Isolation:
CATII (300V) to load negative.
Setting Accuracy:
± 2% ± 200mV.
Volts & Amps:
Measured values of current through and voltage across t he load.
Watt & Ohms:
Power and equivalent load resistance, calculated from Volts and Amps.
Volt age Accuracy:
± 0·1% ± 0.02%FS.
Current Accuracy:
± 0·2% ± 0.04%FS.
Constant Conductance Mode (CG)
(1)
(2)
TRANSIENT CONTROL
Transient Generator
Slew Rate Control
The slew rate control applies to all changes of level whether caused by manual selection, remote
control or the transient gener at or.
The level change is a linear slew between the two level settings. The range available in each
mode is shown above.
Oscillator Sync Output
Connection: Terminal block on rear panel. Lo terminal output grounded to chassis
DROPOUT VOLTAGE
The load will cease to conduct if the applied voltage falls below the Dropout Voltage setting;
active in all modes. The Dropout Voltage setting is also the t hr es hold for the Slow Start facility
and acts as an offset voltage in Constant Resistance mode.
Slow Start
If Slow Start is enabled, the load will not conduct any current until the source voltage reaches the
Dropout Voltage setting; it will then ramp the controlled variable up (in CC, CP and CG modes) or
down (in CR mode) to the Level setting at a rate determined by the Slew Rate setting .
METER SPECIFICATIONS
Display Ty pe: 256 x112 pixel graphic LCD with white LED backlight.
internally. TTL/CMOS (5V) output. High during Level B phase of
Measured Values
6
Output Terminals:
BNC (chassis ground) on front panel or ter minal block on rear panel.
Output Impedance:
600Ω nominal, for >1MΩ load (e.g. oscilloscope).
Scaling:
250mV per Amp (4 Volts full scale).
Accuracy:
± 0·5% ± 5mV.
Isolation:
CATII (300V) to load negative.
Bandwidth limit (-3dB):
40kHz.
1.4 LXI Core 2011 compliant.
USB:
Standard USB 2.0 connection. Operates as virtual COM port.
Capabilities: SH1, AH1, T6, L4, SR1, RL2, PP1, DC1, DT0, C0, E2.
RS232:
Standard 9-pin D connection. Baud rate: 9600.
internally.
Input Impedance:
10kΩ. Input prot ect ed against excess input voltages up to 50V.
Isolation:
CATII (300V) to load negative.
Operating Mode:
The applied voltage sets the operating level within the range.
Scaling:
4 Volts full scale (250mV per Amp).
Accuracy:
± 2% ± accuracy of range.
Common mode rejection:
Typically better than –76dB.
Operating Mode:
The applied signal selects between Level A and Level B settings.
Threshold:
+ 1·5V nominal. A logic high selects Level B.
Input to the LED of an opto-isolator t hr ough 1kΩ resistor.
Threshold:
Apply >+3V to disable the load input. Max. Voltage 12V.
CURRENT MONITOR OUTPUT
REMOTE CONTROL
Digital Remote Interfaces
The unit provides LAN, USB, GPIB and RS232 interfaces for full remote control.
LAN:
GPIB: Conforming to IEEE488.1 and IEEE488.2.
Ethernet 100/10base-T connection with auto cross-over detection.
External Control Input Characteristics
Connection: Terminal block on rear panel. Lo terminal input grounded to chassis
External Analogue Voltage Control
External Logic Level (TTL) Control
Remote Disable Input
Connection: Terminal block on rear panel.
7
will trip into the fault state at 460 Watts.
Protection Current:
The input is disabled if the measured current exceeds a user set limit.
a protection against high power sources
reverse polarity.
Protection Voltage:
The input is disabled if the measured voltage exceeds a user set limit.
suppressors will start to conduct at typically 800V ± 20%.
safe levels.
currents that exceed 20A.
AC Input:
110V–120V or 220V–240V AC ±10%, 50/60Hz. Installation Categor y II.
Power Consumption:
40VA max. Mains lead rating: 6A minimum.
Operating Range:
+ 5ºC to + 40ºC, 20% to 80% RH.
Storage Range:
– 40ºC to + 70ºC.
Environmental:
Indoor use at altitudes up to 2000m, Pollution Degr ee 2.
Cooling:
Variable speed fan. Air exit at rear.
Safety:
Complies with EN61010-1.
EMC:
Complies with EN61326.
Size:
130mm H (3U) x 212mm W (½ rack) x 435mm D.
Weight:
5.7 kg.
Option:
19-inch rack mount kit.
PROTECTION
Excess Power: The unit will attempt to limit the power to 430 Watts; if this fails the unit
Excess Current: The unit will trip into the fault state at nominally 20 Amps.
Excess Voltage: The unit will conduct a current pulse (to absor b induct ively generated
Temperature: The unit will trip into the fault state if t he Mosfet temperature exceeds
Reverse Polarity: The unit will trip into the f ault stat e if a reverse current is drawn that
The unit is protected by fuses that pr ot ect the unit against currents that
exceed 20A. This is primarily as
with a current capability of >20A being connected to the load with
spikes) for 1ms at about 510V.
The unit will trip into the fault state at nominally 530V. Surge
exceeds 200mA. The unit is protected fuses that protect the unit against
GENERAL
Specification Notes
(1)
Slew Rate Ranges refer to the theoretical slope of the transition between two levels,
regardless of whether that t r ansit ion can be achieved when taking into account the level
difference, the set transition dur at ion, t he minimum transition time, and the characteristics of the
source.
(2)
Minimum Transition Time specification is an indication of the f ast es t available transition using
a benign source and low inductance connections, with a minimum terminal voltage of 25V and a
minimum current of 200m A. The actual performance attainable with electronically regulated
power supplies depends on the combination of source and load loop bandwidths and
interconnection inductance.
8
instrument.
l
3. Safety
This instrument is Safety Class I accor ding 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 Ins tallation Category II instrument intended
for operation from a nor m al single phase supply.
This instrument has been tested in accordanc e 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 r etain the inst r ument in a safe condition.
This instrument has been designed f or 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 bet ween +5° and −10°C without degradation of its safety. Do not
operate while condensation is present.
It has been designed for CAT II (Measurement and Overvoltage Category II) use to 300Vrms.
CAT II is local domestic supply level, e.g. portable equipment and appliances.
For this equipment 2500V is the maximum peak t r ans ient overvoltage that can be tolerated by
any load input terminal with respect to earth gr ound without impairing s afety.
Use of this instrument in a manner not spec ified 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 conduct or inside or outside t he inst r um ent will make the
instrument dangerous. Int ent ional inter ruption 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, m aint enance or r epair.
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.
The instrument contains both encapsulated fuses and non-resetting thermal fuses; t hese ar e not
replaceable by the user. The short-circuiting of these protective devices is prohibited.
Do not wet the instrument when cleaning it.
The following symbols are used on the instrument and in this m anual:−
Caution Refer to t he accompanying
Alternating Current.
Mains supply OFF.
9
documentation, incorrect
operation may damage the
CAT II
Measurement and Overvoltage
Category II (300V)
Chassis ground.
Mains supply ON.
4. Installation
4.1 Mains Operating Voltage
The operating voltage of the instrument is shown on the rear panel. Should it be necessary to
change the operating voltage from 230V to 115V or vice-versa, proceed as f ollows:
1. Disconnect the instrument fr om all voltage sources , including the mains and all inputs.
2. Remove the screws which hold the case upper to the chassis and lift off.
3. Unplug all cable connectors from t he power supply PCB (don’t pull on the wires).
4. Remove the five nuts which hold the power supply PCB in place, and lift it off the studs.
5. Fit the soldered links (alongside the transformers) for t he required operating voltage:-
For 230V fit only LK2 and LK5
For 115V fit only LK1, LK3, LK4 and LK6.
These links may be either tinned copper wire or zero-ohm resist or s.
6. Refit the power supply PCB, ensuring that no wires are t rapped. Check that all cables are
correctly connected and that all five nuts are suff icient ly tightened.
7. Refit the case upper.
8. To comply with safety standard requirements the operating voltage marked on t he r ear
panel must be changed to clearly show the new voltage setting.
4.2 Mains Lead
Connect the instrument to the AC supply using the mains lead provided. Should a mains plug be
required for a differ ent t ype of mains outlet socket, use a suitably rated and approved 3-core
mains lead set which is fitted with the required wall plug and an IEC60320 C13 connector f or the
instrument end. This instrument req uires a lead rated at 6A for all mains supply voltages.
Any interruption of the mains earth conduct or inside or outside t he inst r um ent will make the
instrument dangerous. Int ent ional inter ruption is prohibited.
4.3 Mounting
This instrument is suitable both for bench us e and r ack 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 or two of these half-width 3U high units is available from the
Manufacturers or their overseas agents; a blanking piece is also available for unused positions in
the rack.
4.4 Ventilation
The unit is cooled by a variable speed fan which vents at the rear. Take car e not t o restrict the air
inlets at the top, side and bottom panels or the exit at the rear. In rack-mounted s it uat ions allow
adequate space around the instrument and/or use a fan tray for forced cooling. If ducting is
applied to the air outlet, additional extraction is required.
WARNING! THIS INSTRUMENT MUST BE EARTHED
10
4.5 Fuses
4.5.1 Current Range Fuses
The unit is protected by two 10A fuses that protect the unit against currents t hat exceed 20A.
This is primarily as a protection against high power sources with a current capability of >20A
being connected to the load with reverse polarity.
The replacement fuse must be a 10x38mm 10A 1kVdc rated HRC fuse. To replace a fuse:
1. Disconnect the instrument from all voltage sources.
2. Remove the screws retaining the fan guard.
3. Replace the fuse with one of identical specification and size.
4. Refit the fan guard securely.
4.5.2 Inte r nal AC Power Fuse
The AC supply transformers on the PSU PCB is protected against an internal fault by a nonresettable thermal fuse. To avoid the thermal fuse being accidentally tripped by connecting to a
230V supply when the instrument set for 115V operation, a standard 500mA (T) 250V fuse is
fitted in position FS6 on the PSU PCB. Should this fus e need r eplacing , following such an event,
remove the case upper and replace the fuse following the instructions of ‘Mains Operating
Voltage’ section 4.1.
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5. Connections
5.1 Front Panel Connec tions
5.1.1 Load Input
The INPUT terminals for t he load cir cuit on t he front panel accept 4mm plugs. Their maximum
current rating is 16 Amps.
Do not use both the front panel and rear panel terminals simultaneously.
The wiring and connection arrangement mus t be capable of s uppor t ing the current required.
The load circuit is isolated from g r ound, with a rat ing of CATII (300V), but it is essential to
observe safe insulation practice.
Ensure that the source is connected with the correct polarity.
The maximum current throug h t hes e t er m inals is 16 Amps.
The maximum voltage allowed across the load is 500 Volts.
The unit contains a fuse in the load circuit, see section 4.5.
5.1.2 Current Monitor Output
The Current Monitor terminals provide a voltage proportional to the load current flowing with a
scaling factor of 250 mV per Amp (4 Volts for 16 Amps full scale). The output impedance is
nominally 600Ω and the calibration assumes a high impedance load such as an oscilloscope.
The current monitor circuit is referenced to chassis ground, as such is isolated from
the load circuit with a rating of CATII (300V).
5.2 Rear Panel Connections
5.2.1 Load Input
The INPUT terminals for the load circuit on the r ear panel accept 4mm plugs. Their maximum
current rating is 16 Amps.
Do not use both the front panel and rear panel terminals simultaneously.
The wiring and connection arrangement mus t be capable of s uppor t ing the current required.
The load circuit is isolated from g r ound, with a rat ing of CATII (300V), but it is essent ial t o
observe safe insulation practice.
Ensure that the source is connected with the correct polarity.
The maximum current throug h t hes e t er m inals is 16 Amps.
The maximum voltage allowed across the load is 500 Volts.
The unit contains a fuse in the load circuit, see section 4.5.
5.2.2 Terminal Blocks
All other rear panel connections are made via the screw-less terminal blocks. To make
connections to the terminal blocks, use a flat screwdriver to press the spring-loaded orang e
actuator inwards to open the wire clamp; insert the wire end f ully into the hole and release t he
actuator. Ensure the wire is properly gripped. Take care to observe the marked polarity.
5.2.2.1 Remote Disable Input
Apply greater than +3V (preferably +5V) to the DISABLE INPUT terminals to disable t he load
input; these are the input to an opto-coupler, through 1kΩ, and are galvanically isolated from all
other terminals. The input current is less than 2· 5m A at 5V.
The maximum input voltage is +12Vdc. Avoid reverse polarity.
12
protected against excess input voltages up to 50V.
5.2.2.2 Oscillator Sync Output
The SYNC OUTPUT is a TTL/CMOS (5V) output driven by the signal from the internal oscillator ;
this output is chassis ground ref er enc ed. There is a 1kΩ series protection resistor.
5.2.2.3 Remote Control Voltage Input
The CONTROL VOLTAGE terminals are used in two operating modes of the instrument:
In EXTERNAL VOLTAGE mode an analogue signal applied here sets the level of the load; the
scaling is 4 Volts full scale.
In EXTERNAL TTL mode, a logic signal applied here selects either the LEVEL A setting (logic
low) or the LEVEL B setting (logic high). The switching threshold is nominally +1·5V.
These terminals are refer enced to chassis ground. Input impedance 10kΩ. Inputs are
5.2.2.4 Current Monitor Output
The top pair of terminals, mar ked CURRENT MONITOR, provide the current monitor output.
They are wired in parallel with the front panel Current Monitor BNC and the same requirements
apply.
5.2.3 Digital Remote Control Connections
The LDH400P model provides full remote control capabilities through standard LAN, USB, GPIB
and RS232 interfaces. All of these are isolated from the load input term inals of the unit. The USB,
GPIB and RS232 interfaces are connect ed t o c hassis ground, and care must be taken to avoid
introducing ground loops. The LAN interface is isolated by standard network t r ans formers.
Full details are given in the ‘Remote Interface Configuration’ section 10.
5.3 Prospective Fault C urrent Protection
This unit is not intended to act as an overcurrent fault protection device for the source being
tested. However the instrument does contain two 10A, 1000V, HRC fuses that prot ect the unit
against currents that exceed 20A. This is primarily as a protection against high power sources
with a current capability of >20A being connected to the load with reverse polarity, but will also
provide protection against any other prospective fault c ur r ent >20A.
13
6. Initial Operation
This instrument provides a controllable DC load (a power sink) intended for testing all forms of
DC power supply including PFCs, batteries, photo-voltaic cells , fuel cells, turbines and generators
as well as electronic power supply units.
6.1 Organisation of this manual
The paragraphs below are intended to briefly introduce the particular features of this instrument
and the terminology used in this manual. More technical details are given in later chapter s of the
manual.
The next chapter describes the gener al oper at ion of the front panel and its display, followed by
full instructions for setting each parameter. A short chapter then describes the Analogue Remote
Control facilities, including level selection by a logic level signal.
Following that there is a chapter giving som e application not es and implementation details, which
gives more information on some practical difficulties which may occasionally be encountered in
each operating mode, together with some advice on mitigating strategies.
Finally the digital remote control interfaces and comm and s et of the LDH400P.
6.2 Load modes
The power dissipating stage in this load is fundam entally an adjustable current s ink, which
conducts a current that does not depend on the voltage presently applied from the source being
investigated. This is known as Constant Current operation.
An analogue multiplier is used to offer other oper at ing modes in which the current does depend
on the applied voltage in a known way, providing a choice of Constant Power, Constant
Resistance, or Constant Conductance characteristics.
6.3 Constant and Transient Operation
The load offers two independent level settings, referred to as Level A and Level B. Two keys
marked A and B in the
active.
Transient changes in the magnitude of the load are generated by switching between the two
levels. The transition between the two is a straight line at a slew rate that is specified by the user.
The switching between the two levels can be controlled either by an internal transient oscillator,
which has adjustable frequency and duty cycle, or an external logic (TTL level) signal.
There is no restriction on which of the two levels is the larger.
LEVEL SELECT area of the front panel allow the choice of which level is
6.4 Dropout voltage
The primary purpose of the dropout facility is to protect batteries from being excessively
discharged. When the source voltage falls below the Dropout threshold voltage setting, the load
will reduce the current it draws, eventually to zero. This is a dynamic limit, not a latched state, so
if the source voltage recovers above the threshold (as batt eries often do) then the load will
conduct current again.
6.5 Slow Start
The slow start facility causes the current taken by the load to r ise gently, at the rate
determined by the slew rate setting, when the load is enabled or when the source
voltage rises above the Dropout Voltage threshold setting. It also causes the current to
fall at the same rate when the load input is disabled. This facility is particularly useful in
Constant Power mode, to avoid a latch-up condition when the source is started; see the
‘Application Notes’ section 9.
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6.6 Voltage and Current Limit Conditions
The unit has provision for the user to specify limits on the permitted measured value of voltage or
current. If either of these limits is exceeded then the input will be disabled.
6.7 Power Lim it
The unit continuously monitors the internal power dissipation and varies the speed of the fan
accordingly. If the dissipation rises above about 430 Watts, a hardware power limit circuit will
come into operation and attempt to constrain the load current to control the dissipation. The unit
is then operating in a non-linear mode, which will change the stability conditions. If the power limit
circuit fails to prevent the power rising above a slightly higher fault threshold ( per haps because of
instability) then the fault detector will be tripped and the load will cease to conduct.
6.8 Input Condition Lamps
Two lamps above the Input Enable switch indicate the operating stat e of the unit. They are both
off when the input is disabled. The green lamp lights when the input is enabled, and if t he load is
operating normally then the yellow lamp will not be lit.
The yellow lamps lights if the load cannot conduct the required current, with a message on the
status line at the top right of the display distinguishing between the three possible reasons:
• Power Limit: the power limit circuit is operating as described above.
• Dropout: the voltage applied from t he sour c e is below the sett ing of the Dropout voltage.
• Low Voltage: the power stage is in the minimum resistance condition, because the
voltage available from the source is insufficient to maintain the curr ent level req uir ed.
The minimum resistance condition will occur either if t he sour c e is switched off and is not
providing any voltage at all, or if the voltage drop across the connection leads is causing the
actual input voltage at the load to be below its minimum operating level. Note that if the source
voltage is suddenly applied while the load circuit is in this state, then a current t ransient will
probably occur.
If only the yellow lamp is lit, with the green lamp off, then a persistent fault condition exists.
6.9 Fault Conditions
The unit detects (in hardware) the following fault conditions:
• Current above about 20 Amps.
• Power in excess of about 450 Watts (that the power limit circuit has not succeeded in
controlling to the lower threshold as described above).
• Voltage above about 530 Volts.
• Reverse Polarity (current exceeding 200mA) .
• Excessive heatsink temperat ur e.
• Fan failure.
The fault detectors for excess current, power and voltage have filter networks with a
time-constant of a few milliseconds to allow brief transients to be handled.
When any of thes e fault conditions occurs, the input is disabled, so the unit will cease to conduct
current and a fault messag e will be displayed. An excessive current or power condition will
disappear as soon as the input is disabled, but any of the other c onditions will cause t he yellow
lamp only to remain lit, and the message Fault to show on the status line, until it is cleared.
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6.10 Connecting the Loa d to the Source
The INPUT terminals of the load must be connect ed t o t he s our ce to be tested using sufficiently
low resistance and low inductance connections. Inductance in the interconnection can have a
significant adverse impact on the stability of the source and load com binat ion. The wiring should
be as short and as thick as possible. It is es sent ial t hat t he voltage dr op acr os s t he c onnec ting
leads is sufficiently less than the source voltage to leave enough working voltage across the load.
The load input terminals of t he inst rument are floating from ground, and are rated to CATII 300V.
Connection to an AC mains circuit, primary side DC or non isolated bridge rectifier is permitted on
the negative input terminal with a voltage limit o f 500Vdc between the positive input terminal and
the negative input terminal.
Reverse polarity of the inputs is not permitted.
The maximum permissible voltage between the negative input terminal and earth ground
425V (peak of CAT II 300V).
Ensure that all wiring is safely insulated for the working voltage involved.
PFC safe test and operation area diagram
is
6.10.1 Prospective Fault Current
The instrument detects any fault condit ion and r esponds by disabling t he load by turning off the
power devices. As a last resort there ar e internal fuses in the load circuit, so that if the external
source applies a condition so far beyond the current rating of the unit, the f us es will protect the
instrument against dangerously high currents.
6.10.2 Remote Input Disable
This input is provided for remote override of the INPUT ENABLE function of t he load, poss ibly for
safety reasons. It is available in all operating modes of the instrument. It is a fully floating input to
an opto-isolator: apply 3 to 12 volts (observing polarity) to disable the load. The load is only
enabled if this signal is absent and the input has been enabled with the front panel controls.
6.11 Switching On
The line POWER ( ) switch is at the bottom left of the front panel. Before switching on ( l ),
check that the line operating voltage of the unit (marked on the rear panel) is suitable for the local
supply. After switching the power on (
information. Avoid turning off the power until the instrument is fully initialised and the home
screen is displayed.
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l ) the LCD should light and display firmware version
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