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2.11.1 CB37 Terminal Board

The CB37 terminal board from LabJack connects to the U6’s DB37 connector and provides convenient screw terminal access to all lines. The CB37 is designed to connect directly to the U6, but can also connect via a 37-line 1:1 male-female cable.

When using the analog connections on the CB37, the effect of ground currents should be considered, particularly when a cable is used and substantial current is sourced/sunk through the CB37 terminals. For instance, a test was done with a 6 foot cable between the CB37 and U6, and a 100 ohm load placed from Vs to GND on the CB37 (~50 mA load). A measurement of CB37 GND compared to U6 GND showed 29.9 mV. If a signal was connected to AIN0 on the CB37 and referred to GND on the CB37, the U6 reading would be offset by ~29 mV. The same test with the CB37 direct connected to the U6 (no cable) resulted in an offset of only 9 mV. In both cases (cable or no cable), the voltage measured between CB37 AGND and U6 GND was 0.01 mV.

When any sizeable cable lengths are involved, a good practice is to separate current carrying ground from ADC reference ground. An easy way to do this on the CB37 is to use GND as the current source/sink, and use AGND as the reference ground. This works well for passive sensors (no power supply), such as a thermocouple, where the only ground current is the return of the input bias current of the analog input.

2 comments

The guide indicates 16 analog inputs on the U6 with the first 4 on the screw terminals and all on the DB37. Please clarify. Does a DB37 come with it? If not, why not indicate this in the literature? No big deal but very unclear.

I am not totally sure what you are asking, but the normal U6 does come with the DB37 connector.  See Section 2.0.  Section 2.11 also talks about the DB37 connector, while this section (2.11.1) talks about the optional CB37 terminal board accessory (not normally included with a U6).  You can access the I/O on the DB37 connector however you want, but the CB37 is a convenient way.

The U6-OEM does not have the DB37 connector installed, as mentioned in Section 2.13.