|Product Performed to Expectations:||7|
|Specifications were sufficient to design with:||10|
|Demo Software was of good quality:||8|
|Product was easy to use:||8|
|Support materials were available:||10|
|The price to performance ratio was good:||10|
|TotalScore:||53 / 60|
Keithley 2450 SMU with I-V Tracer App RoadTest
By Gough Lui - May-July 2020
For those who may be working with electrochemical cells, primary/rechargeable batteries and semiconductor devices (including diodes, LEDs, MOSFETs and solar cells), the source-measurement unit (SMU) is quite a useful piece of test equipment to have. It can be thought of as a four-quadrant power supply combined with high precision metering all in the one box, achieving compact flexibility to run tests in any polarity, in voltage or current and determining parameters such as resistance and I-V curves with high precision. This makes them very useful devices to simplify testing of components, however, their flexibility does come at a cost which is often out of reach of the hobbyist.
Back in 2013, there was a RoadTest for the Keithley 2450 SMU which I applied for but did not ultimately get selected. Seven years later, thanks to element14 and Keithley/Tektronix, I now have the opportunity to fully evaluate the Keithley 2450 SourceMeter Unit’s capabilities, including the bundled software and the new I-V Tracer App which allows the unit to perform curve tracing without the need for a PC. Read on to find out more about its features, performance capabilities and my thoughts.
If you found this review informative, helpful, entertaining or interesting, I would appreciate if you could please leave a comment, like, rating, bookmark or share it with those who may be interested. Also, if you are interested in more details in any section, feel free to click-through to read the full “in-depth” blog associated with that section.
FINAL Update: 25th December 2020 - Follow Up #6 with Neons, Light Globes, Transient Response & Revised Final Conclusion.
All content post-review delivery will be posted in Update blogs linked at the end of this review to maintain the integrity of this review. Please read this review in conjunction with the updates linked at the end.
Unfortunately, the SMU I received appears to have a hardware fault causing problems with its 200V range and also produces some occasional unexpected readings even at lower voltages when using the I-V Characterizer in KickStart 2. Other minor inconsistencies and inconveniences have also been noted. More details about the instrument’s behaviour is given in the in-depth blog on instrument performance tests.
I have been in contact with representatives from both the Singapore and US branches of Tektronix since 22nd May 2020 reporting my findings and attempting to work through the issues towards a resolution. However, in part due to COVID-19 disruptions, it did not appear that a full resolution of the issues would be forthcoming prior to the deadline for review delivery.
As a result, in order to fulfill the RoadTest review requirements to deliver a full review by the two-month deadline to maintain my standing within the program, to allow me to access further RoadTest applications and as a way to communicate my findings regarding the Keithley 2450 SMU and I-V Tracer App, I have decided to publish this review on time despite these issues. Another reason for this is due to the 60-day time-limited trial of Keithley KickStart 2 licensed software (not included in this RoadTest), which expires soon after this review is posted.
While reading this review, please keep in mind that the unit I received does have hardware faults which can manifest itself as unusual readings, which have resulted in a deviation from the originally proposed RoadTest. Despite this, it has still been possible to evaluate and present most of the user experience, user interface and functionality independent of these faults. An update will be added to the review upon resolution.
A source-measure unit, or SMU for short, can be thought of as a precision voltage/current source and meter in the one unit. Operating over all four quadrants, the SMU is able to source and sink positive and negative voltages and currents. This is in contrast with conventional power supplies and DC electronic loads which operate in one quadrant only. Source-Measure Units improve flexibility at a cost of a more limited power envelope and a more complex and expensive instrument. In return, it makes performing many tests easier due to tight integration and synchronisation, reduces the footprint on the bench or in the rack, improves accuracy and testing speed and reduces the wiring set-up necessary. Applications include I-V curve testing of semiconductor devices of almost every variety (diodes, LEDs, lasers, BJT, MOSFET, IGBT, OLEDs), photovoltaic (solar) cells, batteries, power supplies, thermistors, MOVs, gas-discharge tubes, insulator leakage current, resistances and more.
In order to understand the positioning of the Keithley 2450 SMU, on-paper specifications for bench-top style SMUs were compared. The Keithley family was the largest, consisting of the latest graphical SourceMeters, the older 2400-series and 2600-series. Of these, the graphical SourceMeter range improves on the specifications of the older series while improving flexibility through more connectivity options and programmability, while also incorporating a superior user interface through the use of a 5” capacitive touch LCD. Other vendor alternatives included Rohde & Schwarz/ADCMT, Yokogawa and Keysight, however, some of these appeared to be “unobtainium”, they generally offered lower specifications and more limited user interfaces.
As a result, it seems clear that the Keithley 2450 SMU seems appropriately positioned in the market, with leading specifications and capabilities where it matters, at a price that sits well with the Keithley family of SMUs and those from other vendors. The Keithley SMU range has different units for different needs, making choosing a Keithley SMU feel quite natural. Other vendors have a more limited range of SMUs available by comparison, with the closest match on price and specs perhaps being the Keysight B2901A which doesn’t present any compelling advantages over the 2450.
For more thoughts on the subject, see Keithley 2450 SMU In-Depth: Ch1 – Intro to SMUs & Market Survey.
The unit arrived safely from the USA packaged in a distinct, Keithley-branded double-walled cardboard box. Inside, the accessories are stored in their own zip-lock style plastic bag and the unit is bare (with the exception of an LCD protection cover film), supported at its ends by foam inserts which provide clearance around the unit. This minimal packaging philosophy is more environmentally friendly and seems to be sufficient to keep the unit safe.
The unit’s front panel is dominated by a 5” colour LCD with capacitive touch, with supplementary inputs supplied by eight rectangular rubberised buttons flanking both sides of the display and a push-rotary encoder. There is a hardware power button, USB-A socket for exporting data and screenshots, output on/off and front/rear terminal control button. Front panel outputs are in the form of five safety banana sockets. The rear of the unit offers a fused universal-voltage power input, remote control interfaces including LAN, USB, TSP-Link and GPIB, digital I/O, interlock connection and guarded outputs especially suited for low-level measurements in the form of four triaxial connections. The unit features air vents on all sides except the front and has a plastic carry handle that doubles as a stand, although this doesn’t seem particularly sturdy and can only be set in one of four positions. The unit was lighter than expected and its metal casing exhibited some amount of flex. The unit itself was manufactured 19th December 2019 in China and carries the Australian RCM, making it approved for use in Australia.
The unit has a rather generous accessory bundle which includes safety notices, information about where to find the downloads, information about the included test leads, a plastic-spiral bound colour quick-start guide, Keithley KickStart CD (which is out of date), cross-over Ethernet cable (for LAN or TSP-Link), a USB A to B cable, a US power lead, interlock connector and Keithley 4mm safety test lead kit (1.2m, surprisingly flexible for its 1000V/20A CATIII rating). Unlike some other instruments I’ve received, this unit does away with the calibration certificate and report entirely. If I had any particular wish, it would be for something with a four-wire Kelvin connection to better illustrate more of what the 2450 is capable of without adding too much in the way of cost.
For all the high-resolution photos, please refer to Keithley 2450 SMU In-Depth: Ch2 – Unboxing Introduction.
The 2450 SMU is about as easy to set-up as an instrument can be – its universal voltage input means that it’s basically plug-and-play. Initial set-up included firmware updating the unit from 1.6.7c as shipped to 1.7.1.e which supports I-V Tracer and contains a number of improvements. From there, it was easy to get going.
The user interface consists of a touch-screen interface with buttons flanking either side, the use of both necessary to navigate all of the features. While the main screen looks basic, it is actually packed with features and shortcuts allowing for efficient access to the main settings screens without having to access the main menu. The design of the main menu as a single page with no scrolling makes it easy to navigate the instrument’s full suite of settings at a glance.
The instrument’s configurability is quite varied, with the ability to configure sourcing and measurement separately, the ability to visualise data onboard the device and execute actions using TriggerFlow graphs or TSP scripts.
At first, the interface felt a little intimidating, but it was easy to adjust to and proved to be quite likeable, finding a good balance between ease of use for the beginner and flexibility/efficiency for the power user. My main complaint would lie in the quality of the LCD display which appears to be a TN type, with a more limited viewing angle which makes it harder to view especially if you’re looking down toward the screen. When combined with the slightly matted plastic front layer which seems to have a repetitive spotty pattern, it makes things a little more difficult to see as it reflects the glare from the room lights and reduces the display contrast even with the brightness at 100%.
The other thing of note is the default setting of warning alerts seems to be a little excessive – the interlock warning for example proved to be rather surprising as it was triggered when attempting to source more than 21V, even though it is possible to source 42V without asserting the interlock according to the manual. This proved to be confusing and I have suggested it be looked into for a change. Likewise, there are also limitations to how the SMU handles high impedance output mode and four-wire mode which results in disabling continuous measurement mode which is not automatically re-enabled when the output is enabled.
Executing a battery discharge test was easily accomplished using the SMU alone. Discharging a simulated AA Sanyo Eneloop cell on the R&S NGM202’s Battery Simulator option resulted in a capacity value within 2mAh with an expected sourcing error of around 9mAh, which was extremely impressive.
The full documentation for the SMU can be accessed online, split into a datasheet, user manual, reference manual and security/declassification procedures. The quality of the documentation is excellent, being clear, free of errors (that I could see) and sufficiently detailed. The division between what goes into the user manual and the full reference manual is also well done, such that users who choose to consult the user manual need not be burdened by the full details of SCPI/TSP command listings. Additionally, Keithley/Tektronix also provide quality reference materials regarding making low-level measurements which proved to be quite informative and a great introduction to the intricacies involved and the relative strengths and weaknesses of different types of instruments.
For more information, please refer to Keithley 2450 SMU In-Depth: Ch3 – User Experience & Documentation.
The Keithley 2450 SMU offers a vast array of remote-control connectivity options, including USB, LAN, GPIB, TSP-Link and Digital I/O. The USB interface allows for front-panel usage of USB Mass Storage Devices in FAT/FAT32 format for recording data, settings and screenshots from the instrument and for loading scripts and firmware upgrades. The rear USB interface allows for use as a USB-TMC compliant instrument. The instrument’s LAN interface is compliant with LXI Version 1.5 (2016) as of the latest firmware upgrade, offering a powerful web interface, direct socket and VXI-11 connectivity. The web interface is especially commendable for its implementation of the virtual front panel and buffer download capabilities which makes remote working with the instrument without programming a breeze. The unit offers GPIB connectivity to ensure near-drop-in backwards compatibility with older SMUs with a minimal amount of programming changes while offering an industry-standard bus with hardware trigger synchronisation. Alternatively, the Keithley-specific TSP-Link daisy-chain bus is also supported, along with TriggerLink using an adapter with the digital I/O port. The digital I/O port offers six I/O lines, configurable as input, output or open collector for use as digital bits or trigger, and additionally a Vext line for use with relays, making it a very versatile arrangement for interfacing with both Keithley and non-Keithley equipment.
During testing, I made use of the LAN interface extensively and found it to be reliable throughout the two-week long command sequences used in the Instrument Performance Testing chapter. The consideration of security of the LAN interface through the use of passwords and security levels to prevent authorised use of the instrument is also a first amongst the instruments I have tested, making it less likely for instruments to be accidentally or intentionally misused.
But by far the biggest asset of the 2450 are its large memory buffers, dual-dialect support for SCPI commands and Test Script Processor (TSP) commands, and implementation of TSP scripts through the Test Script Builder (TSB). This allows a break away from the traditional SCPI model of smart host controlling “dumb” instruments, which suffers from bottlenecks due to command transmission and processing latencies which often limit the speed at which these systems can operate and impose synchronisation challenges. Instead, by making a Lua-based programming/scripting language interpreter in the instrument accessible to the user, these issues can be overcome by allowing the test logic (branches, loops) to execute on the instrument directly, storing results into a capacious buffer or front panel USB. When combined with the ability to prepare and debug scripts interactively through TSB, it is a fully-featured Eclipse-based development environment for TSP scripts which makes transitioning from SCPI just that little bit easier. The authored scripts can be saved to USB for loading and executing on the SMU, thereby also allowing users to eschew the use of a PC if they desire.
The only downside to TSP is that it is a Keithley-specific feature that is not otherwise standardised, so any scripts developed are “tied” to Keithley equipment with TSP capabilities. However, that may not be such a big issue for some, as there are ways to use TSP on a Keithley instrument to provide remote control of non-Keithley instruments through the use of tspnet commands. I show how this is done in the chapter on I-V Tracer App Comparison. It’s definitely a powerful feature, and if you don’t like it, well you still have good-ol’ SCPI.
The fun part? You can make your SMU do this ...
For a closer look, please refer to Keithley 2450 SMU In-Depth: Ch4 – Remote Interfaces & Programmability.
The KickStart 2 software is intended as a start-up software to let users get up and running with their instruments immediately without any programming, supporting a range of Keithley and Tektronix products including SMUs, oscilloscopes, DAQs, DMMs and PSUs. It consists of a number of standard apps and add-on apps. It is licensed as KICKSTART-FL-BASE option, with a 60-day fully-featured evaluation period which is used for this RoadTest.
For the SMU, KickStart 2 offers a competent I-V Characterizer app that has support for multiple SMUs with most of the necessary settings allowing for customisation of the sweep type and parameters. It offers a table of values and graph which is updated in real-time as the test progresses, along with a progress bar that offers estimated times. It allows data to be exported in CSV, Excel and PNG screenshot image formats at various resolutions.
Using KickStart 2 and the 2450 SMU, I was able to characterize a variety of devices, including diodes, LEDs, metal-oxide varistors (MOVs) and NE-2 neon bulbs in forward and reverse bias. The exported data was used to build the graphs which show the differences in behaviour between different devices. The data illustrated the superior low-level capabilities of an SMU compared to power supplies and digital multimeters I had previously used, with the background current noise in the tens of picoamps even when using banana leads on the front panel. Previously, I was only able to measure down into the hundreds of nanoamps.
The software generally performed well, with some anomalies experienced likely due to hardware faults in the 2450 SMU that I received. Despite this, I noted the occasional spurious bug that required a restart of the program. KickStart 2 is also a little less flexible than I imagined, as other apps are not available for SMUs. I would imagine something like data logging, similar to what might be available for DMMs, could be easily adaptable to the SMU but is not offered. It was also discovered that the CD included contained the original version of KickStart from 2014 which had issues detecting the instrument when installed on my Windows 10 desktop machine.
Users will have to evaluate whether KickStart 2 provides the functionality and value they expect, as the price of a KICKSTART-FL-BASE license is not inconsiderable and its capabilities are still relatively limited. Of course, if one is comfortable with programming their own solutions either using SCPI or TSP remote control, such options are fully available as an alternative.
For more information, please refer to Keithley 2450 SMU In-Depth: Ch5 – KickStart 2 & I-V Characterizer.
The 2450 SMU offers a number of different on-board approaches to I-V curve measurement – there is the onboard sweep generator and graphing feature, the optional I-V Tracer app and the possibility of using TSP scripting.
The I-V Tracer app is licensed as option KICKSTARTNL-ACT1 which was provided as a claim check by e-mail for redemption through the TekAMS system which generated a license file to be imported into KickStart 2. From there, the app needs to be installed to the SMU on the first use, after which it remains resident on the SMU and can be run without the computer. The claim process was a bit more complex than I had expected and after installation, the system believed I had a one-year trial even though this should not have been the case. It could be related to installation on a trial version of KickStart 2, but I was assured by Tektronix that this should not cause any problems.
The I-V Tracer app is designed to imitate the intuitive operation of a curve tracer by providing a real-time graph of current and voltage, controlled by the rotary encoder knob on the front panel. I found the set-up to be somewhat lacking, especially on the 2450. I found the feel of the rotary encoder to be less “analog” and more “digital” owing to the stepped operation. The knob “acceleration” with regards to speed of rotation is hard to gauge, since the unit plots only 2-3 points per second at the most. Depending on the limit settings, it can be extremely easy to overshoot the inflection point of the curve, requiring a back-and-forth action to try and get more resolution around this point. The output is maintained on during the trace, which means that slower tracing will result in possible heating of the device under test, resulting in deviations of the traced curve. The alternative is turning the knob slowly and consistently, but this results in a very slow trace that may wear out the rotary encoder (and your fingers). Based on my experiences so far, I find the I-V Tracer App hard to consider as a good replacement for a curve tracer, especially when used on the 2450 in its current form.
Some of these limitations seem to be specific to the 2450, because it does not have the high-speed digitisers and AC capability of the 2461, thus cannot offer quite the same experience. I have made some suggestions to Tektronix that they may consider automatically plotting intermediate points while sweeping, adjust the way the knob acceleration works or instead use the touch screen input (e.g. slide your finger to adjust sweep direction and speed) to make a more “analog” feeling tracer. After all, the SMU is quite quick with its outputs, but this app just doesn’t feel like it’s making the most of the capabilities.
Compared to the Sweep Generator and graphing features on-board the SMU, the I-V Tracer offers the user more “direct” control of how the trace proceeds, having some flexibility as to where to spend more “effort” to get clearer data. The downside is that the implementation using the digital rotary encoder and unintuitive-feeling knob acceleration makes this less ideal than it could be.
I-V Tracer can also be used with KickStart 2 connected, in which case it provides a table of data, plotting of the I-V curve on the computer and the ability to export the data. For both the I-V Tracer app and KickStart 2, a number of quirks were encountered which suggests the software could do with some additional polish.
I also explored I-V tracing a MOSFET at several different gate voltages using TSP scripting to control the 2450 to provide the Vds and an R&S NGM202 to provide the Vgs. Using the tspnet commands, it is possible to use the 2450 to also control other vendor instruments over LAN (in this case, using SCPI). As a result, it was possible to perform such an I-V trace without the need for PC connection entirely, storing the data to a locally-connected USB memory device for later processing. As someone who has never written TSP code prior to this RoadTest and has never coded in Lua before, it was exciting to see that it only took about 30 minutes of looking at references to get from nothing to a completed script. The results weren’t perfect, as it seems thermal effects and stray charges may have affected some of the curves, but the SMU shows impressive low-current resolution in this test as well.
For a closer look, see the Keithley 2450 SMU In-Depth: Ch6 – I-V Tracer App Comparison.
The determination of the instrument’s performance is made difficult by the fact that the unit I received is suspected of having a hardware fault, thus is not a typical unit. Notwithstanding this, the 2450’s specifications are generally higher than the instruments I have at my disposal, thus firm conclusions on some parameters can be difficult to draw. Regardless, I believe it was still a worthwhile exercise, even if it was time consuming, so that I could gain some understanding of how SMU performance compares with ordinary power supplies and to have the opportunity to test the unit’s remote-control interfaces over long command sequences spanning a number of weeks.
In terms of instrument stability, in general, I had no issues with remote control using SCPI over VXI-11 LAN for the purposes of the instrument testing, in fact, the Keithley Model 2110 5.5-digit DMM connected via USB used to perform comparison measurements faulted twice in the same timeframe. The testing, however, was interrupted by spurious overheat errors which tripped the output off, which is related to the suspected hardware fault. The instrument generally remained quiet under testing, but when stressed, the fan nestled within the unit becomes audible like a louder laptop with a tonal element manifesting as a noticeable whine. It is not subjectively loud, but is noticeable.
The output programming accuracy in voltage was verified with the 2110 which was able to clearly indicate that the output error was within datasheet ranges despite the 2110’s calibration being 6 years out of date. This is a good indication that both instruments are doing well. When the 2450 is used to judge itself in a combined programming and readback accuracy test, the errors were well within specifications with errors ranging from about 2uV to 4mV depending on range. This level of precision is generally unattainable with even performance level power supplies.
The output programming accuracy in current was more difficult to verify, due to the difficulty of accurate current measurements in general. The margin of error of the 2110 generally was at a similar magnitude or greater than the 2450’s datasheet specifications, thus not allowing any firm conclusions to be drawn, however the absolute difference lines did remain close to zero and generally within the 2450’s margin of error which again illustrates the likelihood that both instruments agree to within their margin of error. Using the 2450 to gauge its output, the errors were well within error margins, achieving errors within 20nA to 50uA depending on the range, however, low current ranges below 1mA could not be adequately tested due to limitations in my test equipment. This illustrates the additional capability of the SMU to be a “true” current source, providing fine, accurate current sourcing capabilities which is generally not achievable with ordinary power supplies.
Further graphs available in the in-depth blog posting link which follows this section.
Testing of the warm-up drift showed a very small amount of drift – on an output of 50mV, the output drifted about 10uV in total, settling in to its final value in close to 25-minutes.
Unexpected power-down behaviour of the supply for positive voltages is good, showing a loss of regulation initially resulting in a slow voltage decline followed by the loss of all output. However, for negative voltages, the initial voltage decline is followed by a short burst of positive voltage before loss of output, meaning that unexpected power down when operating in the negative voltage regime could result in unexpected output, and it is prudent to turn off the outputs of the 2450 before using the mains power switch.
Dynamic load regulation results showed a very rapid regulation response, where slower transitions were tracked by the power supply, including the 1ms and 130ms examples, although there seemed to be some voltage offset at the two load levels of 100mA and 900mA which seems to be ohmic in some regard but should not have appeared especially with the use of 4-wire mode. This may be related to the various instrument quirks. When challenged with the most demanding transitions with times in the 10-15us region while outputting 10V, the supply showed a deviation of about 800mV with recovery in 75-250us. These rapid transitions easily bring most power supplies to their knees, collapsing their outputs to zero with significant recovery times, so in light of that, the SMU handled this case well. There was some output noise and oscillation visible in high-resolution mode every 500ms which seemed specific to the SMU which I did not observe with other instruments – it could be related to the combination of test equipment or the test set-up, so this result is a little inconclusive.
As expected, the power supply has great constant voltage to constant current transition behaviour. It was difficult to provoke misbehaviour, with no overshoot when asked to source 20V/100mA into a 4.7-ohm resistor (470mV). Increasing the voltage to 200V managed to cause a brief overshoot to 600mV for under 5us, despite the rapid application of the output, rising within 15us.
Output from the SMU has been observed to either be “quick”, rising up to the output value within 40us to 1ms, or more leisurely, ramping up over approximately 155-312ms. Turning off the output results in a smooth near-linear ramp of a period of about 4.51-312ms, dependent on voltage. The output toggle rate appears to be fastest when working within a quadrant, achieving around 1.1ms dwell times for each point. Crossing quadrants, the dwell time was closer to 1.47ms. Attempts to do a -200V to 200V step wave showed slew rate limitations which prevented the SMU from reaching the programmed output voltage. However, 0-200V step waves were possible, with rounded edges looking more akin to a sawtooth wave. While the speed based on a simple TSP loop is not as fast as the 1ms dwell time which some performance power supplies advertise, the faster slew rate of the SMU actually makes its output far more accurate even if its maximum output rate is a bit slower.
The digital I/O performance was very snappy, with the input of digital trigger to output generation propagation time of just 400us. The interlock signal was responded to within 1.5 to 3.6ms.
The downside of the SMU is that its power consumption and overall efficiency are lower than an ordinary power supply. At 230V, 50Hz supply, the 2450 idled at around 25W with each Watt of output costing about 2.76W, reaching about 80W when sourcing 20W. The peak efficiency measured was 25%. While efficiency may not be the primary concern of an SMU user, this is perhaps something that is not obvious and is to be borne in mind in case you intend to be using many of them for automated testing in a rack due to power and thermal concerns.
For the full set of test results, please click through to Keithley 2450 SMU In-Depth: Ch7 – Instrument Performance Testing.
Source Measurement Units (SMUs) are specialised, integrated, precision four-quadrant power supplies and metering in the one box. As a leading name in SMUs, the Keithley 2450 SMU belongs to their latest graphical SourceMeter range alongside the 2460, 2461 and 2470, being the most inexpensive unit within the range, specifically targeting lower-level measurements. The 2450’s specifications often are equal to or superior of those of their competitors, giving little reason to look elsewhere.
The 2450 SMU is packaged simply with just a few foam end-pieces keeping it suspended above the sides of a double-walled cardboard box, accompanied by a zip-lock style bag with the paperwork and accessories, minimising packaging waste. It was good to see that the accessories included a set of highly flexible test leads and clips, LAN/TSP-Link cross-over cable, USB A-B cable, interlock connector and power cable. While a colour quick-start guide and safety notices are included, no calibration certificate was included in my unit.
It’s often difficult to balance flexibility with ease of use, but the 2450 does a good job. The unit’s front banana jacks and rear triaxial connections provide versatility for more accurate low-level measurements and convenience for working on the bench. The touch user interface features a one-page main menu with easy access to all the features, but also offers a swipe-screen with shortcuts to the most frequently required settings. The system offers the ability to perform some graphical programming using the TriggerFlow blocks, or the ability to execute more powerful code in the form of TSP scripts. My biggest complaint would be that the screen suffers from limited viewing angles and noticeable glare due to the plastic film overlay, and that warnings are perhaps a little more intrusive than absolutely necessary especially with regards to the interlock status. The documentation for the unit is solid and comprehensive, sensibly separated into a datasheet, user manual and comprehensive reference manual.
The 2450 SMU has a full plethora of interfaces, allowing for connectivity with GPIB, USB, LAN and TSP-Link. Additionally, digital I/O with six flexible lines (adaptable for Trigger-Link) and an interlock safety interface are provided. The remote-control interfaces performed reliably during several week-long SCPI command sequences. The large memory buffers of the 2450 and the integrated Test Script Processor (TSP) programming facilities enable the SMU to run programs within the unit allowing for faster operation and greater flexibility, including controlling other instruments over LAN or saving data to a connected USB flash memory device. It also opens the possibility of running test sequences without PC-connection. The Test Script Builder (TSB) software provides a full development environment for TSP scripts, allowing for connected debugging.
The KickStart 2 software option offers (KICKSTARTFL-BASE) the possibility to use the I-V Characterizer app with the SMU, allowing for PC-connected I-V tracing using up to four instruments without needing any programming. It allows for customisation of the sweep type and parameters and offers a table of values and graph. Data can be exported in CSV, Excel and PNG screenshot image formats, providing an easy way to get up and running.
The other module available is the I-V Tracer App option (KICKSTARTNL-ACT1), which requires KickStart 2 for initial download to the SMU. The I-V Tracer app is designed to imitate the operation of a curve tracer by providing a graph of current and voltage, controlled by the rotary encoder knob. I found the set-up to feel “digital” owing to the stepped operation plotting 2-3 points a second, with unintuitive knob acceleration which often causes overshooting. A back-and-forth action is frequently necessary to obtain sufficient resolution, while the output remains on during tracing causing heating of the device under test. The alternative of turning the knob slowly results in a very slow trace that risks wearing out the rotary encoder. The main advantage of the I-V Tracer app is the direct control of the tracing as compared to a fixed I-V Sweep, however, the implementation seems to be less than ideal. I find the I-V Tracer App on the 2450 difficult to consider as a good replacement for a curve tracer as it lacks the speed and analog precision offered by a simple knob, although this may be improved with future updates. Perhaps the high-speed digitisers and AC capability of the 2461 would allow a better experience with I-V Tracer. I-V Tracer can also be used with KickStart 2 connected, in which case it provides a table of data, plotting of the I-V curve on the computer and the ability to export the data, although some quirks were observed.
It is clear from the performance testing results that the 2450 SMU itself is excellent on the whole. Voltage and current sourcing and measurement accuracies were verified to be well within their specifications. Dynamic regulation response, output generation rate, digital I/O and interlock interfaces all were very fast compared with other general-purpose instruments. Warm-up drift was very small, settling down within 25 minutes. While it is easy to think of an SMU as a combination of a multi-quadrant power supply and precision metering, in reality its performance is “more than the sum of its parts.”
On the downside, my particular unit appears to have a hardware issue affecting the 200V range and perhaps even the regulation of the unit to some extent which may throw quality control into question. Unexpected power-down while sourcing negative voltages could result in the generation of positive voltages, while the electrical efficiency of the SMU seemed to peak at 25%. While electrical efficiency is probably not the primary concern for a precision instrument, this could be a consideration where many units are intended to run together in a rack or instrument room.
Thanks to element14 and Keithley/Tektronix for the opportunity to review the 2450 SMU with I-V Tracer App – I look forward to providing further updates as the issues with my unit are addressed.
Review update sections will be posted in the following section:
With the delivery of the sixth follow-up installment, I consider the re-evaluation of the Keithley 2450 SMU post-repair to be completed in what turned out to be a bit of a marathon "double-RoadTest". I hope you enjoyed the review and associated updates - if you have any questions, feel free to leave a comment. In closing, I'd like to wish a Merry Christmas to all and here's hoping for a better 2021.