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Datasheets and User Guides

App Notes

Software & Driver


2 - Hardware Description

Hardware Description Overview

U3 Hardware Description

The U3 has 3 different I/O areas:

  • Communication Edge,
  • Screw Terminal Edge,
  • DB Edge.

The communication edge has a USB type B connector (with black cable connected in Figure 2-1). All power and communication is handled by the USB interface.

The screw terminal edge has convenient connections for the analog outputs and 8 flexible I/O (digital I/O, analog inputs, timers, or counters). The screw terminals are arranged in blocks of 4, with each block consisting of Vs, GND, and two I/O. There is also a status LED located on the left edge.

The DB Edge has a D-sub type connectors called DB15 which has the 8 EIO lines and 4 CIO lines. The EIO lines are flexible like the FIO lines, while the CIO are dedicated digital I/O.

Figure 2-1. LabJack U3


We have a U3-HV module. We want to monitor two differential lines: one is a 1.5VDC and the other one is around 9VDC. We are not sure how you wire the differential signals, do you use the signal ground for the negative leg or and adjacent port?. Thanks


One problem up front is that the high-voltage analog inputs on the U3-HV don't really support differential readings.  Only single-ended.

Where do these signals come from?  Is there a common ground?  Is there common-mode voltage?

I would check out Section 2.6 and the Differential AIN App Note and continue this discussion on one of those pages.

Does the U3 have internal switches that can be used to route the EIO lines on DB15 connector to any of the screw terminals?


The U3 does not have any sort of patch through options. The best it can do is read an input and send that information to a host. The host then has to decide what to do with that information. Response times are going to be 2+ms.