Introduction
My name is Seth Price and I am an instrumentation instructor in the Chemical Engineering department at New Mexico Tech, as well as a National Instruments Certified LabVIEW Associate Developer. The LabJack U3-LV integrates with LabVIEW, and so I was excited to test out this system.
Rather than focusing on the intricate technical details, I wanted to demonstrate what was possible with the LabJack U3-LV within the first hour of installation. The LabJack installation provided a suite of programs that can be used for simple data collection or output. I focused on testing the device out of the box and starting LabVIEW integration.
Installation
The installation was simple. I first plugged the LabJack U3-LV into the USB port. As expected, Windows 7 did not find drivers. However, a quick look on the easy-to-navigate website led me to the drivers. Once I installed the drivers, Windows had no trouble identifying the device, and the LabJack U3-LV was ready-to-use in a few minutes.
Once the LabJack was installed, I put several pairs of wires into the screw terminals for three of the “Flexible I/O” terminals and one ground terminal, FI06, FI07, FI04, GND, respectively. I used these for testing the “Flexible I/O” by alternating between analog inputs, digital outputs, and single-ended versus differential mode measurements.
The LabJack U3-LV comes with a small screwdriver that was a tight, but sure fit in the screw terminals. The terminals gripped the wires securely. For a permanent application, I would recommend some strain relief.
I also downloaded the LabVIEW drivers and sample Virtual Instruments (VIs, or LabVIEW programs) to explore. The LabJack website has some starter VIs as a free download.
The first set of tests was to see how the LabJack performed out of the box. I started LJControlPanel, and selected “Find Devices”. The LabJack U3-LV was found quickly and I navigated to the test panels.
Analog I/O
My first test was to place a used AA battery across terminals FI04 and ground. I configured FI04 as an analog input (AIN4), in Single-Ended mode. Because there was no common ground, I ended up wiring the negative battery terminal to the GND screw terminal. The test panel read 1.465 V, which I then verified with my multimeter as well.
My second test was to place the used AA battery across terminals FI06 and FI07, wiring the negative terminal to FI06 and the positive terminal to FI07. Then, I configured the terminals in the test panels such that FI07 was in differential mode to FI06. Once again, the test panel read 1.465 V. So far, so good.
Digital I/O
I also tested the digital output from the LabJack U3-LV. I wired my multimeter to the FI06 and FI07 terminals. In the test panels, I was able to configure these as digital output lines. A check mark signified a high signal (3.25 V, according to the multimeter), and an unchecked box was a low signal (~ 0V). I tried all four binary combinations (00, 01, 10, 11) between the FI06 and FI07, and they behaved as expected.
The LabJack U3-LV could be connected to a solid-state relay and used as a simple on-off controller. The device could read an analog input, such as voltage from a thermocouple, then output a digital control signal to a solid-state relay to switch on a fan or heater.
Advantages
There is a real advantage to the flexible I/O system developed by LabJack. It is really neat to be able to programmatically change a port from an analog input to a digital output without a lot of effort. Many similar-priced devices have assigned analog and digital channels, making the LabJack U3-LV a more versatile instrument.
I also liked the DB15 connector for additional digital I/O lines. 8 of the lines are flexible I/O lines (EIO0-EIO7), having a standard connector and cables is always a nice touch. There is an optional relay board, RB12, that plugs into this connector, allowing the LabJack U3-LV to control multiple solid state relays.
Integrating with LabVIEW
LabJack is not a National Instruments product. Therefore, it will not show up in NI Max, or be accessible with the DAQ Assistant. However, LabJack has provided a driver bundle and an assortment of sample VIs to get started.
The sample VIs are worth reviewing. Unlike many third party packages, the LabJack VIs are transparent and easily understood with a few minutes of study. These VIs can be modified and saved under a different name, or referenced as needed.
Within a few minutes, I was able to modify one of the existing VIs to select an analog input channel to read. In another hour, I could have had a thermocouple reader/logger up and running.
Conclusions
In my first hour, I was able to measure analog voltage input, send digital output signals, and modify LabVIEW code to take data measurements from the LabJack U3-LV. Its versatility and affordability make it a good choice for small instrumentation and control projects.
The LabJack U3-LV is also well-suited for the academic laboratory environment. With the flexible I/O channels, students can use the same module for multiple instrumentation projects. It is compact and rugged enough for a backpack, but also has a screw hole for permanent mounting in the laboratory.