Omega Engineering PCI-DAS1200 manual A /D Board, Common Mode Voltage +/-10V / Single-Ended Inputs

4.2.3 Common Mode Voltage < +/-10V / Single-Ended Inputs

This is not a recommended configuration. In fact, the phrase “common mode” has no meaning in a single-ended system, and this case would be better described as a system with offset grounds. Anyway, you are welcome to try this configuration, no system damage should occur, and, depending on the overall accuracy you require, you may receive acceptable results.

4.2.4 Common Mode Voltage < +/-10V / Differential Inputs

Systems with varying ground potentials should always be monitored in the differential mode. Use care to ensure that the sum of the input signal and the ground differential (referred to as the common mode voltage) does not exceed the common mode range of the A/D board (+/-10 V on the PCI-DAS1200). The diagram below shows recommended connections in this configuration.

		rce		mon
	al Sou		om
n
Sig		ith C			Voltage
		w	ode
		M				 
					G N D

The voltage differential betw een these grounds, added to the m axim um input signal m ust stay w ithin +/-10V

CH High

CH Low

LL GND

I/O

C onn ector

+

Inp ut	To A /D
A m p

-

A /D Board

S ignal source and A /D board with com m on m ode volta ge connected to a differential input.

4.2.5 Common Mode Voltage > +/-10V

The PCI-DAS1200 will not directly monitor signals with common mode voltages greater than +/-10V. You will need to either alter the system ground configuration to reduce the overall common mode voltage, or add isolated signal conditioning between the source and your board.

Is o la tio n

B a rrie r

arge com		mon
					￿￿
L	e	voltage	signal
mod		een
			&	A/D board
	betw
		source

G N D

C H IN

+

In p u t

LL G N D

I/O

C o n n e c to r

A m p

-

To A /D

W h en the voltage difference betw een signal source and A /D boa rd ground is large enough so the A /D board ’s com m on m od e range is exceeded, isolated sig nal conditioning m ust be add ed.

A /D Board

System w ith a Large C om m on M ode Voltage, Connected to a Single-Ended Input

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