|Product Performed to Expectations:||9|
|Specifications were sufficient to design with:||9|
|Demo Software was of good quality:||9|
|Product was easy to use:||10|
|Support materials were available:||8|
|The price to performance ratio was good:||7|
|TotalScore:||52 / 60|
Table of contents:
A source meter is basically a few instruments combined into one, to facilitate testing and characterizing. It can be used as a power supply or electronic load to source or sink power, and can also be a multimeter to measure voltage, current, resistance.
A comparison between the 2450 and B2961A which is around the same specs and price range:
|Header 1||Keithley SMU 2450||Keysight B2961A|
|Current||10 nA – 1 A||3.03A|
|Wideband Noise||2 mVrms Typ||3 mVrms|
Linear, Log, Dual Linear, Dual Log, Custom, Source-Memory (SCPI 2400 Mode)
|linear, logarithmic (log) or list|
SCPI (2400 + 2450) + TSP Programming
GPIB, USB, Ethernet (LXI)
|GPIB, USB 2.0, LAN and digital I/O (LXI Core Conformant)|
|Measurment Capability||6.5 digits||6.5 digits source resolution and 4.5 digits measurement resolution|
Same type of packing as when I got the DMM6500 from Tektronix a couple of years ago, excellent packaging, the unit comes very well protected.
The unit came with a lot of extras:
- Power cable (US)
- Quick start guide and safety notice
- Old version of Keithley KickStart on a CD
- Ethernet cable
- USB cable
- Interlock connector dongle
- 2 Test leads
The SMU2450's case is slightly bigger than the DMM6500, however both would still fit in a rack cage if needed.
One thing I consider as a great improvement is the built in stand, as you can see in the photos below the 6500 comes with 2 small legs that do not give a robust feel, whereas the 2450 has a one piece stand that can be tucked underneath if not needed.
In order to download the IV-Tracer app that was bundled in this roadtest, firmware needed to be upgraded from version 1.6.7c to the latest version which is 1.7.1e.
The firmware upgrade was a simple procedure, following the instructions provided I downloaded the latest firmware image from the website. then followed the procedure below.
6. Software, support material:
The documentation that came with the device was extensive, the scanned document below pointed out all the support material and software to be used with the device:
The sourcemeter has many applications, I tried to demonstrate practical use cases that I often use at work.
This application is about equipment operating in hazardous environments. A low power device running on 11 cells of Li-Ion batteries and a solar cell need to have a protection mechanism to prevent battery cells from charging eachother, this introduced a lot of complications to the calculated battery capacity. the snippet below is from IEC 60079-0
After many enquiries if there is a protection mechanism between the cells then they are not considered a parallel combination.
And here the SMU came in handy to compare different components at various load levels that will cover the working range of the device.
The schematic below shows an ideal diode configuration
The schematic below shows a schottky configuration
using the same settings as the first application in Kickstart
The SMU was very helpful for quick testing over the working range of the device, the two important values were at 40uA for sleep mode and 50mA when the GPS modem is searching for a fix.
This application in particular is something I spent 3 months doing in the past while preparing to propose changes to the current standards of characterizing and validating inverters. I would have appreciated having a sourcemeter at hand instead of a big setup of programmable power supplies and data loggers.
A bit of theory:
PV modules are manufactured as strings each containing a number of cells, Usually each string or few cells are connected with a bypass diode for protection, if the diodes were not connected then the shaded cells might conduct in reverse mode which will cause the cells to overheat and cause a permanent damage to the module known as hotspots .
Lots of factors affect the shape of the IV curve like the irradiance, temperature, number of cells, how cells are connected, how much of the cells are shaded, the depth of shade and the type of cells. The shade pattern, depth and rapid irradiance changes represent the dynamic conditions that affect the output of the PV modules that is fed into the inverter.
Partial shading on a module decreases the output net energy yield of the whole array drastically, by bypassing these poor output cells one major issue occurs which is a deformation in the IV curve and also the power curve of the whole module. As seen in the figure below the deformation causes a huge loss in output power and introduces more than one local maximum power point; this is where inverters face difficulties tracking the global MPP, so more losses occur due to system failure in producing the maximum potential power.
This is where source meters can come in very handy for testing various IV curves, with different types of deformation to monitor the inverter behaviour and accuracy in tracking MPPT.
A - Using the front panel:
Procedure from the user's manual :
Set up the solar cell I-V sweep from the front panel
This is an example of an I-V test that sweeps voltage from 0 V to 5 V in 10 mV steps and
measures the resulting current. You can then view the data on the graph screen.
To set up the application from the front panel:
1. Make connections to the instrument and device under test (DUT) as described in Device
connections (User's Manual P.92)
2. Press the POWER switch on the front panel to turn on the instrument.
3. Reset the instrument:
a. Press the MENU key.
b. Under System, select Info/Manage.
c. Select System Reset.
d. Select OK.
4. Press the HOME key.
5. Press the FUNCTION key.
6. Under Source Voltage and Measure, select Current.
7. Press the MENU key.
8. Under Measure, select Settings.
9. Set Sense to 4-Wire Sense. A warning is displayed.
10. Select OK to clear the warning.
11. Press the MENU key.
12. Under Source, select Sweep.
13. Set the Start level to 0 V and select OK.
14. Set the Stop level to 5 V and select OK.
15. Set the Step level to 100 mV and select OK.
16. Swipe the SWEEP SETTINGS screen until you see Source Limit.
17. Set Source Limit to 1 A and select OK.
18. Select Generate. This sets up a trigger model for the sweep.
19. Press the MENU key.
20. Under Views, select Graph.
21. Press the TRIGGER key to initiate the trigger model. The output turns on and a RUN indicator is
visible at the top of the screen while the sweep is running.
22. Press the trigger key again to repeat the sweep.
The following note is from the user's manual:
B - Using IV-Tracer:
C - Using Kickstart IV-Characterizer:
I created the same configuration in the figure below using a small prototyping breadboard to demonstrate the use of a source meter in characterising IV curves.
(all measurements were taken indoors, so current values are very low, and not accurate since it wasn't measured at STC).
One of the solar cells was covered to show the effect of a bypass diode and how the SMU can be useful in capturing the curve.
The 2450 is rated up to 200V however I tried different loads and the highest voltage I was able to source was around 43V. I spent some time trying different loads but just couldn’t pinpoint the source of the problem. I will post an update when I hear back from Tektronix. The photo below is from a resistive load rated at a maximum of 80W, highest voltage reached was 42.8V.
This is a problem I encountered a few times, Kickstart is not meant to control the app IV-Tracer, which is understandable since it defeats the purpose of using the rotating knob.
But sometimes when I try to capture the measurements I get the following error. I attached a photo of the system monitor to show that there is no actual memory problem.
The SMU 2450 is one of those devices that I never thought of buying until I tested it and now I think how did I even manage in the past without it. The device is packed with features that are definitely a great help to any engineer to verify calculations and simulations. In my case its main advantage is the quick test setup. I believe it can also be very helpful for quality control process for production of semiconductors, thermistors, solar cells, and other components.
Main limitation of the 2450 is the 1A current limit, which limits its potential. I would recommend a minimum of 3A, this will open doors to a much wider range of applications and instead on just focusing on semiconductors it will include all types of modems (cellular/GPS/BLE/…etc), which also means that the SMU can then be used to characterize operating range for embedded systems and IoT applications, battery profiles and current peaks.
Hopefully the next firmware upgrade will solve the issue of capturing data from IV-Tracer in Kickstart.
I seem to have missed using the interlock connector [MPN: CS-1616-3], which was the reason the output voltage in section 7.4 was limited to around 42V.
Once connected, the 2450 can source voltages at the full range of the device up to 200V.
When pins 1 and 2 are connected using a jumper wire, and the connector is plugged into the back of the unit, the green Interlock led at the front panel switched on.
IV-tracer data is captured in KIckstart:
After further experiminting with the device, I couldn't source more than 10W at >100V range.
Fans do not start and I got the following issue in the photo.
After reporting the issue to Tektronix, their invistigation resulted that when operating on the 200V rail at certain voltage and current levels, the ranging circuitry can start to oscillate. This causes the instrument to falsely believe it's overheating and shut down.
I had a very good experience with their support team and their reply was quick, they identified the fix which will require sending the unit to them.
 Model 2450 SourceMeter® Instrument User's Manual
 R. E. Hanitsch, Detlef Schulz and Udo Siegfried. "Shading Effects on Output Power of Grid Connected Photovoltaic Generator Systems." Technical University Berlin, Institute of Electrical Power and Automation Technology Sec. EM 4.