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U3 Datasheet

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LabJack U3-HV Low Cost USB DAQ Device Picture

Affordable multifunction DAQ with USB.

This datasheet covers all U3 variants:  U3-LV, U3-HV, U3-LV-OEM, and U3-HV-OEM.

These HTML pages form the complete datasheet, manual, and user's guide for the U3.  Most information in this datasheet applies to all U3 variants.  There is an OEM section with information specific to the build of OEM versions.  There is a Hardware Revision section that describes variations due to hardware revisions 1.20, 1.21 and 1.30.  Specifications are in Appendix A.  UD library documentation is in Section 4.


Reading This Document

Searching The Datasheet

To search this datasheet you can just use the search box you find on every page, and to further refine your results include "u3" or "u3 datasheet" in your search term.  To specifically restrict your search to just this datasheet, include "site:labjack.com/support/datasheets/u3" in your search term.  For more information see the main Search Page.

Table of Contents Note

Navigating using the Table of Contents Table of Contents button on mobile

An efficient way to navigate this online document is to use the Table of Contents button to the left.

Offline PDF Note

Offline PDF

If you are looking at a PDF, hardcopy, or other downloaded offline version of this document, realize that it is possibly out-of-date since the original is an online document.  Also, this document is designed as online documentation, so the formatting of an offline version might be less than perfect.

To make a PDF of this entire document including all child pages, click "Save as PDF" towards the bottom-right of this page.  Doing so converts these pages to a PDF on-the-fly, using the latest content, and can take 20-30 seconds.  Make sure you have a current browser (we mostly test in Firefox and Chrome) and the current version of Acrobat Reader.  If it is not working for you, rather than a normal click of "Save as PDF" do a right-click and select "Save link as" or similar.  Then wait 20-30 seconds and a dialog box will pop up asking you where to save the PDF.  Then you can open it in the real Acrobat Reader rather than embedded in a browser.

Rather than downloading, though, we encourage you to use this web-based documentation.  Some advantages:

  • We can quickly improve and update content.
  • Click-able links to further or related details throughout the online document.
  • The site search includes this document, the forum, and all other resources at labjack.com.  When you are looking for something try using the site search.
  • For support, try going to the applicable page and post a comment.  When appropriate we can then immediately add/change content on that page to address the question.

Periodically we use the "Save as PDF" feature to export a PDF and attach it to this page (below).


It would be most helpful if this user guide could be expanded to describe installation and use with Mac OS X and Linux.  Not all of us use Windows.

Good comment.  There should at least be pointers on where to go for Linux and Mac, so we will address that.


Looking at the first link on the U3 user's guide webpage it says: http://labjack.com/support/u12/users-guide

Shouldn't the link point to the U3 and not the U12 guide or are they so similar that it doesn't matter?



Fixed the typo.  We recently added that remark for the sake of people who might be looking at a pdf or harcopy version of this user's guide.

Is there any way that the font on the export all could be increased?

I second this.  I exported & printed, and I honestly cannot read print this small.

Will this be the thing that drives me to reading glasses?


Your link to the PDF version is broken.

When you click "Export all" the server creates a PDF on-the-fly using the current content.  This can take 20-30 seconds for many web pages like we have with the U3 User's Guide.  If your browser times-out too quick you can get an error from your browser.

Try a couple more times and if it still does not work contact [email protected] so we can look into it further.  You can also use the "Print all" link if you want to print a copy.  This is much faster because it does not convert to PDF.

I just sent an e-mail to [email protected] with a copy of the screen shot. For some reason, I was not able to properly attach it here in the comment section.

When I click the link "Export All", the .pdf does not show properly. Everything after section 2.13 is there but doesn't show. For example, if I search the document for the word "program", the word is found in a Sections 2.13, but there is not text visible. Is the link broke or did I do something wrong? Thanks!

I don't understand "everything after section 2.13 is there but doesn't show".  When I search for "program" in the PDF, it is not found in Section 2.13.  The closest place it is found is the 4th paragraph of Section 3.1, and when I go there I see it and all the text fine.

I tested with Google Chrome and have the latest Acrobat Reader installed.  Also, I added more information to the page above.

I bought a labjack U3-LV module and Lj Amp to connect with Load cell. please advise me how to read the load value. Software installed and view the set up.


I can control two Labjacks U3-LV in one process basing on labjackUD.lib. One process means one command window running my test code. For example, test code running in a dos command window can power on/off both labjack HBA 0 and labjack HBA 1.

However, I failed in control labjacks in multi-process. I wanted to let No.1 test running in No.1 command window control Labjack HBA 0, and concurrently, let No.2 test running in No.2 command window control Labjack HBA 1. I did not make it. If I run No.1 test first, the No.1 test can list out the two U3 Labjacks connected and get the handler of each Labjack, then No.1 test control labjack HBA 0 correctly. During No.1 test running, I start No.2 test, although No.1 test and No.2 test use same test code for labjack, this No.2 test can not list out Labjacks and can not get handlers. Even if I use inter-process technique to pass the Labjack HBA 1 handler address from No.1 test to No.2 test, the No.2 test will still fail in control power on/off. I think the different process have different memory mapping, so the labjack HBA handler address in process 1 is not valid in porcess 2.

Does Labjack U3-LV support multi-process control? If yes, how to do that?

Thank you very much in advance.

Is there any way to close labjack or release labjack during program running?

There is a function in the driver void Close() which will free all resources in the driver and return it to its initialization state.  Generally it is meant to be used as a debugging function or for very specific cases.

I would like to have "next topic" (or "next section") and "previous topic" links at the bottom of each page.  Not so necessary at the top, where the sidebar navigation is visible, but some sections are long enough that that scrolls out of the browser viewport, and if you're reading through in order (typical noobie behavior, I'd guess ... and I fall into that category for this device) then having access to the next page  right where you're looking is very helpful.

The module we are using to organize this content does not support that at this time, but we will keep your feedback in mind for an update.

This is a weird question, but will the LABJACK accept LIN communication it is serial (UART kinda)?

The U3's UART can be used to communicate with a LIN hardware transceiver. Which can then connect to other LIN devices. The higher-level protocol will have to be implemented in host software.


Also, there may be an issue if you want to use the U3 as a slave device. It will take a few millisecond to receive and respond to a command. If the LIN master is unwilling to wait that long there may be a communication failure.


Is possible to connect this DAQ module with accelerometer for measuring vibrations?


If you get a nice voltage signal, then you can measure it with the U3.  See Section 2.6.3 of the U3 User's Guide and forum topic #6120.

rbsexton's picture

The PDF has badly-converted tables in the specification section.     I understand the appeal of web docs, but you really need a functional PDF thats ready to go.   You can't search a set of web pages.   I'll take a real document over a web page any day.

labjack support's picture

We generated a new PDF. The Specification tables are no longer cut off on the right side.