Measurement Computing CIO-DAS16/M1 - Manual (Page 9)

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3.2.1 Analog Inputs
The CIO-DAS16/M1 has eight differential analog input channels. Each channel has a signal-high input
and a signal-low input. The measurement made by the A/D is the voltage difference between the LOW
and HIGH inputs. Differential inputs have a common mode range (see application note). The CIO-
DAS16/M1 can have as much as 10V of common mode voltage between LLGND and signal LOW.
CAUTION
Measure the voltage between the ground signal at the signal source and the PC. Use a voltmeter and
place the red probe on the PC ground and the black probe on the signal ground. If there is more than 10
volts, do not connect the CIO-DAS16/M1 to this signal source because you will not be able to make any
reading. If the voltage is over 20V, DO NOT connect this signal because it will damage the board .
3.2.2 Connecting Analog Inpu ts
Connect analog inputs as shown in Figure 3-2 below. Pay close attention to cabling and grounding of the
shield. Failure to cable as shown will result in signal noise.
NOTE: Failure to cable as recommended will cause less than perfect readings. Perform signal wiring with
consideration to the high speeds involved. Even if your A/D pacing rate is not high, the converter is
always converting at less than 1
µ
s and the internal MUX switching is done at a similar high speed.
NOTE: Keep high and low wires together. Keep the signal wires for a channel together. Ideally, they
should be a twisted pair. This will aid the differential inputs in rejecting EMI or RFI from input signals.
3.2.3 Shielding
To further protect the input signals from noise, use shielded cable. Shielded twisted-pair cable is readily
available. Connect the shield as in the diagrams below or ground loops and signals noise may result.
3.2.4 Grounded Signal Source
A grounded signal source has the low signal referenced to chassis ground. If an instrument has only two
poles, HI and LOW, it is probably referenced to chassis ground internally. Check with an Ohmmeter
between LOW and the power cord ground prong. If an instrument has three poles, a HI, LOW and GND,
you can strap LO to GND as shown here, or use the connection for Floating Signal Source.