R&S 4-Output Bench Power Supply, Prog (HMP4040.04) - Review

Table of contents

RoadTest: R&S 4-Output Bench Power Supply, Prog (HMP4040.04)

Author: Gough Lui

Creation date:

Evaluation Type: Independent Products

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: Various other power supplies from Keithley, GW-Instek, Aim-TTi, B&K Precision, Keysight, RIgol and ELC were considered, but no true four-channel power supply was identified.

What were the biggest problems encountered?: Product was damaged in shipping, resulting in a partial failure of the device. RoadTest was still completed nonetheless, awaiting final resolution.

Detailed Review:

Rohde & Schwarz HMP4040.04 Programmable Power Supply Road-Test Review

By Gough Lui – October-November 2018


After being extremely fortunate to have been chosen to RoadTest the Rohde & Schwarz RTM3004 Oscilloscope Kit, I was pleasantly surprised and honoured to have been selected for another opportunity to review some serious gear. Thanks to element14 and Rohde & Schwarz, I present my RoadTest review of the Rohde & Schwarz HMP4040.04 Programmable Power Supply.


While reading this review, keep your eyes peeled for the occasional Easter Egg – there are no prizes on offer (sorry), but I thought it was worth including given the recent furore about the GNU Overhead badge.


Market Survey

When it comes to power supplies, the term “channel” is used very loosely. While normally referring to independent floating outputs, many of the supplies on the market feature dissimilar capabilities between channels. If you are in the market for a four-channel power supply, guess what? There aren’t many choices at all. If you’re willing to settle for three, there are a few more choices, but many of them only possess two equal channels with an “auxiliary” channel that has additional limitations (e.g. fixed voltages, limited current, limited protection).


But even more than this, the total power rating and channel power rating is also something that can catch buyers unaware. Some supplies have “discrete” ranges of voltage/current limits which must be respected which can leave you unable to use all of the “rating” depending on your operating voltage.


As a result, while the R&S HMP4040.04 was the most expensive supply in the round-up, it is the only true four-rail power supply I could find. Unlike other supplies, the four rails on the supply are equal in capability which is important for flexibility in parallel/series operation and maximising the use of the power rating. Also, unlike many of the supplies in the round-up, the voltage/current ranges for each rail are “continuous” rather than in fixed sub-ranges which further improves flexibility. While you do pay for the 160W per channel and 384W total, you’re much more likely to be able to use it more often. It also saves space, as it is only marginally larger than some of the lesser alternatives and of similar weight.


The downside compared to the other supplies mainly lie in the monochrome LCD which is somewhat outmoded by the newer colour LCDs, limited default connectivity of USB/LAN (relegating GPIB and RS-232 as options) and lack of internal series/parallel operation which can result in cable clutter.


While the price of the HMP4040.04 may seem high, considering that the unit is truly four identical channels which are much more flexible in regards to channel load balance, the price doesn’t seem as bad once you realise that for quite a few configurations, the third rail of “2+1” style supplies might not be useful at all. Add to this the Hameg Instruments heritage of this design, the Rohde & Schwarz reputation backed by a three-year warranty, and it’s clear that the HMP4040.04 does have a distinct position within the market that few supplies could match.


To learn more about the intricacies about power supply ratings and what’s on offer, see R&S HMP4040.04 PSU RoadTest in Depth – Ch1: Market Survey.



The HMP4040.04 is a rather hefty beast. The packaging seems rather simple but appropriate with a thick double-walled sturdy outer box, a cardboard inner wrap around the supply, protective film on scratch-sensitive components and generous clearance from all sides through the use of foam ends. The supply comes with a calibration certificate, printed quick-start manual, full complement of power cords and fuses to cover international operation. While no data cables were included, they are extremely common and their omission is of no great issue.


The supply features a relatively large front panel display, rotary dial and direction-button input along with a full direct-entry keypad. Connections are made by shrouded banana plug jacks, which are safer for high voltage use but not as convenient as binding posts. Direct wire connection can be made at the rear, with the remote-control interface card being user replaceable.


The unit is designed with a stackable feet design, with copious ventilation holes at the top and vents to both left and right of the unit.


However, unlike previous unboxings, instead of having a pleasant experience, this was more of a “crime scene” being documented. Rather unfortunately, the shipping carrier didn’t take any care to deliver the package with the respect it deserved, resulting in significant damage to the power supply unit within, including a warped chassis, bent I/O plate on the HO732 card and potentially further damage to the internals which are not assessable from the exterior.


As a result, this RoadTest was interrupted to submit the necessary documentation for an insurance claim to the shipping provider. Apparently, the insurance is still in the process of being finalised. In my opinion, the carrier was negligent in transporting the unit as it was clear that the box was rounded at most edges, holes were punctured into the double-walled box, the box was not transported in its correct orientation to my door and the delivery person had even “dumped” it unceremoniously onto the concrete floor during delivery. I was not going to sign for it, but the staff member motioned for me to sign it claiming it was “probably just bubble wrap crumpling”. As a result, I am still awaiting a resolution to the damage.


To some degree, Rohde & Schwarz may want to take note of this and further bulletproof their packaging. Adding bands around the foam itself, to ensure the power supply cannot “escape” the foam ends even if the double-walled box were to be collapsed would ensure there wouldn’t be a case where a hard “drop” of a crushed box would allow the chassis to make hard contact with the inside cardboard. The weighty nature of the power supply means that any free movement of the power supply relative to a “hard surface” would probably result in the damage that was seen, so an even more sturdy outer box may be necessary to avoid corner deformation that could allow the supply to move within the box. It may add a slight cost to the packaging, but if it avoids damage due to negligent couriers, it could be very much worth it.


To see the (not-so-pretty) pictures, see R&S HMP4040.04 PSU RoadTest in Depth – Ch2: Unboxing.


Standalone User Experience & Features

Using the Rohde & Schwarz HMP4040.04 in a standalone fashion reveals that the supply is the product of very sensible design decisions. While it may appear somewhat old due to the use of a monochrome display, it is bright and large for easy reading with an acceptable viewing angle. The use of a direct-entry keypad allows for more rapid entry of numeric values, while directional keys and a rotary knob allow for alternative ways to adjust values. Colour-coded LEDs are used to denote channel selection, operating status and input modes which can be understood at a glance. The method of operation is intuitive and easy to get acquainted with, and the menu set-up is relatively straightforward and logical.


More importantly, the layout of the power button in the top left and the master output button in the top right makes it easy to identify by feel in case of an emergency to allow for rapid de-energising of the load. The presence of the sense terminals that require no manual configuration eliminates the potential for misconfiguration and saves hassle. The sure-fire isolation provided by relay-controlled outputs provides an added level of reassurance.


I was especially impressed by the low noise of the cooling system even under full load for an hour. Using an unconventional cross-flow design, the fans start imperceptibly and run at a continuously variable speed. The fans are powerful and capable, demonstrated by the self-test sequence on power-up. However, in a regular open room with a full load, the fans ran nowhere near their maximum and were only barely audible above my computer fans. The amount of margin available should ensure reliable full-load delivery even in demanding situations such as rack-mounted configurations with elevated ambient temperatures.


The downsides identified included the omission of rail sequencing on the device (e.g. power up delays between rails), limitations with monochrome LCD display data (no display of output set-points and metering simultaneously), the use of shrouded banana connectors that may not be ideal for use with thicker wire or bare wire, the small shrouded terminal blocks on the rear which make thicker wire difficult to use, the lack of internal series/paralleling which can result in external wire clutter and inconsistencies in the IP address entry menu which requires a lot of knob-spinning to enter an address.


It is also worth noting that the HMP4040.04 also offers an integrated electronic fuse for protecting devices under test (DUT) with configurable delay for capacitor charging in-rush currents. While this doesn’t emulate a real fuse (as it is a hard current limit), it is useful where a current-trip (OCP) behaviour is desired. FuseLink functionality allows for multiple outputs to trip “nearly” simultaneously, thus avoiding damage in the case of multi-rail DUTs.


The HMP4040.04 also offers an over-voltage protection (OVP) based on measured or configured voltage that also protects the DUT against over-voltage. Finally, the EasyArb functionality allows for sequences of pre-defined voltages, currents and delays to be generated from the power supply without the assistance of a computer.

In all, I found the HMP4040.04 to be featureful, highly performant, easy to use on the bench and with a sensible traditional design. The only drawbacks identified are relatively minor in my opinion, some of them are personal preferences and many of them are common to other supplies on the market as well. As a result, I’d have to say that the HMP4040.04 does a good job when it comes to user experience.


To see more of what the power supply has to offer, see R&S HMP4040.04 PSU RoadTest in Depth – Ch3: Standalone User Experience & Features.


PC-Connected Remote Operation

The full power of the HMP4040.04 is realised when it is used in connection with computer remote-control for automated testing. To this end, Rohde and Schwarz provide a comprehensive support library of software drivers and examples for IVI.NET, LabView, VXIpnp, C#, MATLAB and VBA to name a few.


The HMP4040.04 comes with an HO732 USB and LAN interface board installed, providing either USB-CDC (COM port), USB-TMC (VISA) or LAN based connectivity. This can be exchanged for an HO720 for USB and RS-232 interface or HO740 for a GPIB interface, however, no other forms of analog/digital control interface appear to be available. Drivers for the HO732 are not required for CDC operation, with USB-TMC drivers covered by the installed VISA manager, making installation straightforward. It was discovered that the USB mode is not memorised through a power cycle, defaulting to USB-CDC operation at every boot-up.


The HO732 currently does have one disadvantage compared to the HO720/HO740, as this interface is not currently able to be used to update the firmware on the HMP4040.04. Rohde & Schwarz have indicated that this is a problem that they are looking towards resolving – which is important as another issue with the EasyArb functionality which requires a firmware rectification was identified.


The LAN interface offers a basic web interface offering the ability to read settings, take a screenshot and send SCPI commands. Unfortunately, the interface is as basic as it gets, without any password protection, front panel emulation or live screen updates, making it somewhat underwhelming. SCPI Direct connection allows for socket-based direct control, as is standard for most LAN-connected instruments.


HMExplorer is the software specifically intended for use with R&S HMP-series instruments (formerly Hameg). The software offers a scriptable SCPI terminal with command reference, screenshot tool and EasyArb configuration tool. The latter is the most useful, allowing for easy definition, visualisation, import and upload of arbitrary waveforms to the HMP4040.04. While the installation of HMExplorer was without difficulty, I was not able to get USB-TMC connectivity through my installed VISA manager to operate and the screenshot tool recorded only truncated screenshot files.


Through testing, it was determined that the EasyArb functionality does seem to have a limitation where waveforms are not replayed continuously if they have 127 or 128 points. Rohde & Schwarz have informed me that they are aware of this issue and it should be corrected in an upcoming firmware update.


R&S Forum is a more general piece of software intended for automating test equipment in general and appears to be a Python 2.7 based application that mimics an IDE in its design and uses its own visa_pytron engine for communication. More sophisticated than RSCommander, it offers fairly similar capabilities in automating a standalone install of Python and related tools so that users can automate their testing more easily.


It was possible to use the HMP4040.04 with my existing install of Python and pyvisa and direct SCPI command was achieved although I did find some anomalies with command synchronisation and buffer handling (which could be entirely my fault). Using fixed delays seemed to work just fine with an occasional retry necessary – although this could be due to the damage that the unit sustained during shipping which resulted in unresponsiveness of the interface altogether and necessitated power cycling.


The SCPI command-set for the instrument treats each of the channels as if it were a separate instrument, necessitating selecting the channel (INST:NSEL 1) before issuing commands that alter the state of the channel. The global output switch is controlled (OUTP:GEN 1) separately to the activation of the channel (OUTP:SEL 1). This took a little time to get used to. There were several cases where there was more than one command to achieve a certain outcome, with additional commands to step increment/decrement values being a nice touch.


Out of curiosity, I gave the included MATLAB and Excel/VBA examples a go and found them functional, albeit the Excel example did seem to show some command synchronisation issues as well.


For more information, see R&S HMP4040.04 PSU RoadTest in Depth – Ch4: PC-Connected Remote Operation.


Instrument Performance Testing

I’ve put the HMP4040.04 through my barrage of tests and its performance can only be described as unimpeachable. Despite the shipping damage, the unit’s insulation was uncompromised and the unit was (at least initially, fully) electrically functional.



While each rail is slightly different, voltage programming accuracy was extremely tight with most of the results showing agreement with a 5.5-digit DMM within the margin of error and being well within the claimed accuracy levels. The voltage read-back accuracy was slightly poorer, but still well within the claimed limits. Current programming and read-back accuracy was even more impressive, again being mostly within the margin of error of a 5.5-digit DMM. All of this, when considering the power supply was operating in a non-temperature-controlled room off raw mains power which has noise and voltage variations. This suggests that Rohde & Schwarz have been extremely conservative with their specifications to ensure they will be met even under adverse operating conditions and that the unit was well calibrated from the factory, not drifting much despite the abusive shipping conditions.


Channel-to-channel power-up timing varied by about 2.73ms owing to the relay-controlled output and potential mechanical variances at play, which is still quite acceptable. Rail ramp-up and ramp-down times were a swift ~2ms and ~16ms respectively.


Overshoot into constant current mode was observed, with the overshoot magnitude being greater for a higher voltage, but the recovery is also more rapid at higher voltages. In the tested cases, the constant current regulation was achieved in 4-7ms after the channel comes up – a very rapid response. Testing this, I connected a 5mm red LED to the outputs, set to 32V at 50mA and cycled the output multiple times. The LED survived seemingly undamaged – where doing the same thing to some other supplies had resulted in the LED being destroyed at the first cycle. This demonstrates just how responsive the regulation loop is.


Transient regulation was tested informally using a DC electronic load. While the load was able to provoke some voltage excursions, this is not unexpected at high slew rates. On the whole, the response was very quick and any excursions were very limited in duration. If anything, it demonstrates that the load is faster but the power supply is still very quick to respond.


Attempting to quantify the noise and ripple was more difficult owing to difficulties with ensuring a balance of bandwidth and noise levels. In the end, I was not able to conclude much about the actual ripple voltage amplitude, however, it seems that there is significant ripple at 175khz and also noise at 5 and 7Mhz which might not be appreciated by LF/HF radio loads. This noise appears to be present whenever the power supply is switched on, even with the outputs disabled.


Finally, it was determined that the power supply was able to operate throughout the voltage range required with some additional margin. Internal monitoring is able to inform the user when the power supply outputs are unstable and when the voltage has dipped too far.


The only potentially major issue was the behaviour of the rails when power is removed from the power supply unexpectedly. In the test case, an unloaded 1V rail rose to 10V as the hardware power switch was actuated – so it’s best to turn off the rails first using the output button before turning off the power to the supply to ensure the DUT is not damaged. Another observation was a ~30W power consumption of an idle power supply with outputs switched on. This is a significant draw, but if the supply is not in use, the hardware power button can be used to bring the draw down to zero.


To see all of the juicy test details including test code, see R&S HMP4040.04 PSU RoadTest in Depth – Ch5: Instrument Performance Testing.



The Rohde & Schwarz HMP4040.04 is a rather unique and flexible four-channel power supply which draws upon the Hameg Instruments heritage and offers a three-year warranty. With four channels of equal specification with no fixed sub-ranges, it is possible to combine channels externally in series and parallel to achieve a wide range of operating conditions with very few restrictions compared to the competitors. While it is the most expensive supply in my market survey, it is also the most flexible, with the majority of other supplies marketed as three channel units but really only having two main outputs and one lower-powered auxiliary outputs. Depending on whether you can make use of the auxiliary channel, the HMP4040.04 could replace two of these “2+1” channel units in a smaller package, making the price somewhat justified.


The HMP4040.04 comes packaged in a sturdy cardboard box with generous clearances from all sides and foam ends. Included are power leads and fuses to cover all regions, calibration certificates and a printed quick-start guide. Unfortunately, despite the adequate packaging, the unit arrived damaged in transit. As a result, the test results obtained may not be truly reflective of a “to-specification” unit. My particular HMP4040.04 suffers from intermittent loss of remote-control capability and a loss of functionality on the fourth channel, limiting some of my testing.


In standalone use, the sensible design of the HMP4040.04 made operation rather intuitive and straightforward. Taking advantage of the large front-panel area, direct keypad entry, directional button and rotary knob control are provided for. The large monochrome LCD is somewhat old-fashioned and can only show the current metered voltage/current/power or the set-point voltage/current/power at any time, but is backlit and can be configured to be easily read. Colour coded LEDs shine through the buttons to allow for “at-a-glance” understanding of channel status. The addition of arbitrary waveform generation, OVP and OCP with FuseLink capabilities are helpful, and the cooling solution is well designed such that in the case of full-load room-temperature operation, the fan noise is unobtrusive with a mostly “white” spectral character.


But the full potential of the HMP4040.04 is realised when connected to the PC for remote control. With extensive support with examples provided for various different development environments, along with a downloadable detailed manual with a full list of SCPI commands, integration is made easier. Dedicated software in the form of HMExplorer allows for some automation and easy import/export of EasyArb data. R&S Forum allows for Python-based automation as well, although I also found pyvisa to be usable as well. MATLAB and Excel VBA examples were also tested with success.


When put through the gauntlet of instrument tests, the HMP4040.04 was beyond impressive with voltage and current programming accuracies which are mostly within the margin of error of my 5.5-digit DMM. Voltage readback accuracy was slightly lower, but was still very much within specification suggesting a very conservative specification sheet to handle operation even under adverse conditions. Rail-to-rail synchronisation along with rail rise/fall times were swift - measured to be around 2.8, 2 and 16ms respectively. Constant current overshoot was quickly bought into line within 4-7ms, allowing direct connection of even a 5mm red LED to the rails configured at 32V/50mA without being damaged by the turn-on transient. Transient regulation was also quite rapid, but quantification of ripple and noise was not possible. The power supply also monitors the power input and issues warnings for instability or power failures.


The main functional downsides to the HMP4040.04 include the electronic fuse functionality which is a “hard” limit rather than emulating a real fuse. The supply does not seem to offer a rail “sequencing” feature. The front panel shrouded banana plug connectors, while safe, may not be the most convenient for all users. The rear-panel shrouded terminal blocks are also a little small for larger gauge wire. The supply does not offer an internal series/paralleling feature, which may require additional external wire clutter to achieve. The monochrome LCD is unable to show both set-point and measurements at the same time. The menu does not allow for direct entry of IP addresses and the menu does not memorise the USB connection mode across power-cycles. It was also determined that there is a glitch with the EasyArb functionality for 127/128 sample-long waveforms which cannot be replayed continuously which would require a firmware update to rectify. Unfortunately, it was also determined that it is not presently possible to use the included HO732 to update the firmware – an issue that Rohde & Schwarz are currently working on. The screenshot tool within HMExplorer doesn’t seem to work correctly either and the outputs can become “unregulated” upon a sudden removal of power.


In all, I find these issues to be relatively minor in comparison to the exemplary performance demonstrated in all aspects and the vast number of features that have been explored and tested in the course of the RoadTest review. The HMP4040.04 really does perform as you would expect from a device bearing the Rohde & Schwarz badge and is commendable as one of the only true four-rail supplies on the market.


Thanks to element14 and Rohde & Schwarz for giving me the opportunity to RoadTest the HMP4040.04. It is my hope that the shipping insurance claim can be finalised soon and an undamaged unit can be tested in a similar way (and the review updated). If approved to dismantle the damaged unit, a teardown and investigation into the failed channel will also be attempted along with some of the original proposal items that were not achieved in time. However, in spite of some of the oddities experienced with this damaged unit, the HMP4040.04 still performed extremely well and must be commended for enduring such extreme handling while remaining mostly functional.


Don’t forget to leave a comment, rating, like or bookmark the content. If you want to know more, click-through to the detailed sub-sections which have greater detail about testing methodology and results. Finally, if you’re interested to see what I’ve been up to, you can always visit my personal blog at https://goughlui.com.



[01/12/2018] - Updates to the review will be posted in the R&S HMP4040.04 PSU RoadTest in Depth – Addenda as they are discovered. As of this update, a better understanding of the USB-TMC behaviour of the HMP4040.04 has been developed, a second attempt at measuring command rate is made and the use of the HMP4040.04 in an automated test set-up with a B&K Model 8600 to characterise a boost converter is explored.


Top Comments

  • Thanks for the reply .


    Indeed, it turned out all three units RoadTested suffered some damage in transit judging from the reviews - but I don't think that's entirely R&S's fault judging from the punctures through the double-sided cardboard and even just witnessing my local delivery driver carrying the box the wrong way and slamming it into the ground on my porch. With the clearance from all sides, sturdy foam and double-wall box, it should not have received the damage it did if the shipping carrier were a little more respectful of the package. That being said, if R&S did do something to make it even more robust, that would be ideal as the failure seems to relate to the outer box being damaged badly enough to deform sufficiently to allow the unit to "escape" from its foam end-pieces and thus move about in the box. I've had instruments packaged worse arrive fully intact and in better condition - so I'd have to say the carrier's handling was probably the main difference.


    I am still yet to hear back from about what's happening with it, as I did comply with the necessary claims procedure - once I have been green lighted, there may be a tear-down to add to this too. Until such time, everything (including packaging) is being preserved for evidence at the request of the carrier.


    - Gough

  • Nice detailed review - thanks for your efforts.


    I do think you are a bit kind in your comments -  other companies manage boxes that don't break (and at least one other reviewer of this supply had transit damage issues.)


    The noise and lack of any built in support for channel combining rule this box out for me - I was doing a job (testing low noise 100MHz bandwidth amplifier) today needing 4 linked supplies but I couldn't have used the HMP4040 because of the noise.



  • Just a short comment to let everyone know that updates will be posted in a separate blog post:

    R&S HMP4040.04 PSU RoadTest in Depth – Addenda


    As of this update (01/12/2018), I develop a better understanding of the USB-TMC behaviour of the HMP4040.04, a second attempt is made at measuring command rate and the use of the HMP4040.04 in an automated test set-up with a B&K Model 8600 to characterise a boost converter is explored.


    - Gough

  • Dear ,


    Indeed, the noise is "real" ... I was struggling to understand it myself and relocated the supply several times away from computers, disconnected USB/LAN leads, changed scope probes, shortened the wires connecting to the jacks, but it seemed to be always there. There were some other background noise spikes, but I suspect because we were sampling such low-amplitude AC noise, that some of that noise is internal to the scope itself, radiated from power cables, etc. I tried my best to use bandwidth limiting and 1x probes to minimise the scope noise contribution, but in the end, I'm still not able to accurately characterise the ripple and noise conclusively. That being said, the regulation performance was rather impressive, so maybe the noise is a side effect of a "tight" high-bandwidth control loop circuit.


    The other possibility is that the noise is digital in nature and incidental to the operation of the supply (e.g. each of the channel's microcontrollers might be communicating over an SPI bus at several Mhz, or maybe the LCD's internal controller is making some noise), but whether it was radiated or conducted was not something I could clearly determine either. Switching converters in even hybrid linear designs do create noise, but I was expecting less high-frequency noise.


    That being said, I can't rule out the possibility that my unit was creating more noise than originally intended owing to the shipping damage, and the lack of a dedicated "power rail probe" makes my readings merely an inconclusive attempt. But it was something I wanted to try nonetheless, and I have learned from trying.


    Indeed, the FFT on the RTM3004 is quite snappy - I've used some others which really bog down and can't give a finer resolution. You really do need the memory and processing power to do it - so I guess I'm putting the RTM3004 to good use image.


    - Gough

  • Hi Dr. Lui - thanks for the thorough review and feedback!  It was my pleasure to help out, even while out of the office.  We'll follow-up with the items I mentioned that are planned for future firmware updates.


    -Rich @ Rohde

  • Good review!


    I see you found the same issues I did. I had to unplug almost everything around here in order to make sure that noise in the ham bands was real.


    That scope's FFT is amazing. I was so bummed when I didn't get selected.



  • Thanks everyone for the positive responses - it's great to wake up after a long marathon writing effort to see that my efforts have been appreciated. I do appreciate that it's a long read, and that's not something that everyone can tolerate, so feel free to take some time to digest it image. I just regret that it didn't go more smoothly, with the shipping damage really throwing a spanner into the works. I just hope that the carrier does end up following through with the insurance claim so that and won't get chased around by me about it (sorry!) and the review updated. Of course, I am still grateful for the opportunity nonetheless, as this unit has very much been a superb performer despite the damage.


    Also, many thanks to for being so attentive to my queries and suggestions, even while away from the office.


    As usual, if anyone has any questions - feel free to ask and I'll do my best to answer them.


    - Gough

  • Very thorough road test and an excellent read.


    Kind regards

  • Excellent road test report.


    Well done.



  • Very nice roadtest on this monster of a power supply.  Looks like I still have a bunch of blogs to read through to get the whole story.

    Well done!