Source voltage, measure current, get data
The ability to control instruments is a key skill for experimental scientists and engineers. We’ve designed the Ossila Source Measure Unit so that no matter what your skill level is, you can access affordable, precise instrumentation. Accelerate your data collection today with this versatile, high-performance and low-cost measurement device.
The Source Measure Unit incorporates two voltage source meters for measuring current and two voltage meters for measuring voltage. With it, you can measure a wide range of research devices including photovoltaics, LEDs and OLEDs, transistors, and more. This product is covered by our FREE 2-year warranty and is eligible for FREE worldwide shipping.
What is a Source Measure Unit?
The basic working principle of a source measure unit (also called an SMU or source meter) is very simple - it outputs a voltage and measures the current that flows. In this respect, it is just like a bench-top power supply. However, it is programmable and allows the user to sweep the voltage over a defined range. It is also considerably more accurate than a regular power supply.
The Ossila Source Measure Unit features dual source measure and voltmeter channels and is perhaps our most versatile piece of equipment to-date.
Five current ranges
Choose between five separate current ranges to suit your experimental needs
Flexible & scalable communication
Connect the Source Measure Unit via USB or use several units at the same time via Ethernet connection
User-friendly PC software
No coding experience required! The included PC software comes with pre-set modes, allowing you to perform simple measurements
Portable data exports
All test data can be saved in csv format for convenient analysis in your favourite software package
Software-controlled current ranges
For safety and convenience, the current range switches can be controlled using the included PC software - no need for manual adjustment
Wide language compatibility
All common programming languages (LabVIEW, Matlab, C, Java, Fortran, Python, Perl etc) are compatible with the unit
The Source Measure Unit is a professional alternative to old-fashioned and outdated bench top source-measure units at a fraction of cost. Ossila's product was thoroughly tested by us, it had to compete with state-of-art devices and to our surprise it won the race in all categories: precise PV measurements, networking capabilities, flexibility of programming language and smooth operation in pretty tough chemical/material science laboratories. The Ossila team has delivered a game changer for all of the PV community.
Adam Surmiak, PhD Student in Excitonic Systems for Solar Energy Conversion
Monash University, Australia
Source measure units output a controlled voltage and measure the current that flows. Many everyday objects will have been tested with a source-measure unit as part of the production and quality control process. If you use LEDs to light your home or have solar panels on your roof, these will have been tested with a source measure unit as part of the quality control process.
Source measure units are similar to bench-top power supplies only in their basic operating principle. SMUs are orders or magnitude more precise, are fully programmable, and allow the user to sweep the voltage over a defined range.
With a bench-top power supply you usually use a dial to select the voltage you want to generate, and then look at the display to read off how much current is flowing through your circuit. Usually a bench-top power supply will output a voltage from zero to 12 or 24 volts and measure the current to the nearest milliamp (1 thousandth of an amp) or so. This is great when measuring the current used by motors or light bulbs or high power devices. However, if your want to make precise scientific measurements, then a milliamp is actually a huge amount of current - very often it is necessary to have a precision of microamps (1 millionth of an amp) or nanoamps (1 billionth of an amp) to characterize many electronic devices.
It is important to separate the function of a source measure unit from a regular multimeter; both are very useful but have different purposes. A standard multimeter can measure voltage and it can also measure current - but not at the same time. It also doesn't output a voltage. A good handheld multimeter will be able to measure voltage with an accuracy of a few hundred micro-volts and current to an accuracy of a micro-amp or so - much better than a bench-top power supply. As such, you could also build a source-measure unit with moderate accuracy by using a bench-top power supply to output a voltage/current and two good quality multimeters - one to measure voltage and the other to measure the current. However, this still wouldn't be programmable and also wouldn't allow negative voltages to be measured very easily (both of which are important for many applications).
For some applications it might not be important to have a programmable instrument - you may just want to read off the value once or a small number of times. However, in many cases you might want to collect lots of data so that you can plot a graph or measure the performance of something over time, or link several pieces of apparatus together. However doing this manually is time consuming and difficult. There are also lots of different experiments that require automated data collection to get faster or more accurate measurements, or to take measurements over a long time-scale (months or even years). Here, you will certainly need a computer to collect your data and export it to a spreadsheet or database for analysis.
Not all experiments will need negative voltages - and in some cases, you can avoid this. However, many different types of devices work differently if a positive or a negative voltage is applied. To fully understand how such devices work, we need to be able to change the sign of the voltage applied.
As an example, consider a diode - a device that only allows electricity to pass through it in one direction. In order to evaluate if a diode is working, we need to see if it can pass electricity in both directions. We can do this in one of two ways. We can measure the diode in one direction, then manually turn it around and measure it the other direction, and then 'stitch' the data sets together. More simply however, we can just measure current flow when we apply either a positive or negative voltage. In fact, this technique is so useful it is used to characterize many types of devices that have diode-like behavior - solar cells and light emitting diodes are both very good examples of this.
Measurement of a Solar Cell with a Source Measure Unit
An application that effectively demonstrates the use of a source measure units is the measurement of new solar cells. Rather than build a full-scale cell, researchers will often characterise the performance of a small-scale test device. These devices are much too small to generate any usable power, but are big enough for determining the efficiency of the design.
The efficiency of a solar cell can be determined by shining a known amount of light power over the area of the cell and calculating the electrical power produced per unit area. Since power is simply voltage multiplied by current, a starting point is to measure the applied voltage and the current produced per unit area.
We can measure the voltage generated simply by placing a multimeter across the solar-cell terminals while it is illuminated. Similarly, we can also measure the current using a multimeter; and if we divide this by the area of the solar cell, we get the current density.
However, if you multiply the voltage by the current (or current density) then this only tells us how much power (or power per unit area) we can generate if we had a perfect device. The reason for this is that a good voltmeter has a very high (near infinite) internal resistance, and when we measure the voltage by itself no current can flow and hence no power is generated. Similarly, a good ammeter has near zero internal resistance so when we place the multimeter across the terminals to measure the current we are testing the device when it has been short-circuited.
For any practical (real) solar cell, the voltage that it outputs will depend upon how much current is being produced. A source measure unit is able to vary the voltage and measure the change in current.
The graph below shows a typical JV curve for a prototype perovskite solar cell. The 'J' in JV stands for current density, and the 'V' stands for voltage. The JV curve tells us how the voltage and current are affected by one another and allows us to calculate the actual amount of power that a solar cell generates.
If we multiply the voltage by the current density we get the power density produced by the solar cell, as plotted below. The peak of the graph is the point at which maximum power is generated (the so-called maximum power point).
In the above graphs, we also measure the solar cell when a negative voltage has been applied (so-called reverse bias). This tells us that the device doesn't break down under reverse bias, which is a sign that the device is of good quality.
Secondly, it tells us whether there is any extra current available that we are not making good use of, as by applying a negative voltage we can effectively "suck" charges out of the device that wouldn't otherwise be extracted. While these "sucked" charges can't be used to generate power, they allow us to understand some of the photocurrent loss mechanisms.
Measuring JV curves is one of the most important tools used in solar-cell development and optimization. Similarly taking IV and JV curves is hugely important to understanding a wide range of other device types including LEDs and OLEDs, transistors, sensors and many more.
The source measure unit contains four instruments on one board - two SMUs (voltage source, current sense) and two precision voltage sense channels. There is also a general-purpose shutter/trigger which enables it to control (or be controlled by) other instruments.
Source Measure Units (SMU 1 & SMU 2)
The SMUs output a voltage and then measure both the voltage and current. The output voltage is always measured on the output to the BNC, rather than assuming it is at the set voltage. This is to account for any load effects, for example, short circuiting the output, or low impedance causing a small drop in voltage. Each source measure unit has multiple current ranges, so that you can measure both large and small currents with accuracy.
Voltage source specifications
|± 10 V||10 mV||333 µV||170 µV|
Voltage measure specifications
|± 10V||10 mV||50 µV||10 µV|
Current measure specifications.
|1||± 150 mA||± 200 µA||10 µA||1 µA|
|2||± 20 mA||± 10 µA||1 µA||100 nA|
|3||± 2 mA||± 1 µA||100 nA||10 nA|
|4||± 200 µA||± 100 nA||10 nA||1 nA|
|5||± 20 µA||± 10 nA||1 nA||0.1nA|
Precision Voltage Meter Specifications (Vsense 1 and Vsense 2)
The voltage meters are designed to accurately sense small voltages while also having a wide dynamic range (±10 V).
|±10 V||10 mV||50 µV||10 µV|
The Shutter/Trigger can be used either as an input or an output. It can be used to send a trigger signal to other instruments or configured to wait for a trigger from other instruments. The voltage level of this BNC is 5V - any higher may cause damage to the port.
The X200's user-friendly design will work almost any programming language (at least anything that supports either serial COMs or Ethernet, which is nearly everything commonly used). Common languages that can be used to interface to it are:
|Computer Connectivity||USB-B and Ethernet|
|Measurement Connections||BNC connector|
|Dimensions||Width: 125 mm
Height: 55 mm
Depth: 185 mm
The Ossila Source Measure Unit includes a software Front Panel that enables you to start taking measurements as quickly as possible. With the program you can control each SMU and Vsense channel independently, allowing you to perform many of the most common electrical measurements.
Control both SMU channels
Set voltage and measure current with two independent SMU channels (voltage source, current sense)
Quickly measure voltages
Accurately measure small voltages with the two Vsense channels
Easily set sampling rates
Set sampling rates (OSR) for the SMUs and Vsense channels via the interface
Uses portable data formats
Save data as a portable spreadsheet (.csv) file or a text (.txt) file for analysis with your favourite software package
We also have software for performing specific measurements with the Ossila Source Measure Unit. These can be downloaded for free from our software and drivers page. The currently available measurements are:
- I-V curves
- Solar cell characterisation and lifetime
- Four-point probe sheet resistance
|Operating System||Windows 10 (32-bit or 64-bit)|
|CPU||Dual Core 2 GHz|
|Available Hard Drive Space||116 MB|
|Connectivity||USB 2.0, or Ethernet (requires DHCP)|
The Ossila Source Measure Unit is perhaps our most versatile piece of equipment. It can be used in a wide range of applications; most lab-scale devices that require electrical characterisation in the DC (or low frequency) range (between ±10 V and ±150 mA per channel) can be measured with an SMU.
We have used our X200 SMU to develop systems for measurements for sheet resistance (Four-Point Probe), IV curves and OLED lifetime (OLED Lifetime System and Solar Cell IV Test System), and cyclic voltammetry (the Ossila Potentiostat).
For complete 'out-of-the-box' measurements, please see the measurement systems on our Test and Measurement page. For guides on how to program the source measure unit, please see our Getting Started page. For programming in Python, please see our more extensive Scientific Python Tutorials.
To the best of our knowledge the technical information provided here is accurate. However, Ossila assume no liability for the accuracy of this information. The values provided here are typical at the time of manufacture and may vary over time and from batch to batch.