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How can I measure higher voltages (> +/- 10V) with a USB DAQ...

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How can I measure higher voltages (> +/- 10V) with a USB DAQ device?


Most USB DAQ devices have +/- 10V as their highest input range.  However, several MCC models have higher ranges:



USB-2404-60   This model has a fixed input range of +/- 60V, and provides channel-to-channel isolation.



USB-2416 series    This model offers a +/- 20V range on both single-ended and differential channels.  Both the + and the - leads must be kept within +/-20.01 volts of the GND terminal.  Note that the USB-2416 offers bank isolation (between the I/O signals and the USB bus), so until you connect one of its GND terminal to an outside potential, the +/- 20.01 volt limit does not have an established anchor. 



USB-1208HS series   This series offers a +/- 20V range when set to 4 channel differential mode, however neither the + nor - pin can vary more than 14 volts from PC/earth ground.   So it is possible to correctly measure a 20 volt (or -20V) difference between the + and - leads, as would be the case if +6V (with respect to PC/earth ground) is on one pin, and -14V (with respect to PC/earth ground) is on the other pin.



USB-1208LS, USB-1208FS, USB-1408FS, USB-7204, miniLAB 1008 *   These 5 models share a similar front-end architecture.  They offer a +/- 20V range when set to 4 channel differential mode, however neither the + nor - pin can be > +20V, or < -10V, away from PC/earth ground.  



Resistive voltage divider    For any USB A/D model (not just the ones listed above) you may wish to consider creating your own resistive divider to step down your voltage.   It is best to choose an A/D model with a high (> several megohm) impedance. 

* Note that since the 5 models listed in the last group above have an input impedance of only about 120 KOhm, using a resistive voltage divider is not recommended, as measurement accuracy will be greatly affected.



External active (powered) isolation module   While MCC does not offer cables or backplanes to interface to them, single channel isolation modules do exist on the market.


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Article ID: 50361

Last Modified:5/21/2012 4:05:33 PM

Article has been viewed 4,529 times.

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