Floating Signals - Measurement Computing CIO-DAS16/M1/16 User Manual

3.3.3 GROUNDED SIGNAL SOURCE
A grounded signal source is defined as having the signal low referenced to chassis ground. If an instrument has only
two poles, HI and LOW, it is probably referenced to chassis ground internally. It is easy to check with an Ohmmeter
between LOW and the power cord ground prong. If an instrument has three poles, a HI, LOW and GND then you can
strap LO to GND as shown in Figure 3-2, or use the connection for Floating Signal Source.

3.3.4 FLOATING SIGNALS

A floating signal source is defined as having the signal low with no reference to earth ground (PC Chassis ground or
LLGND). Examples are a battery, an isolated precision power supply or a sensor which is not earth grounded.
A reference between signal LOW and LLGND must be provided because the CIO-DAS16/M1/16 inputs are
differential. Failure to supply the reference resistor (10K) will result in unrepeatable readings (Figure 3-3).
Signal High
Signal Low
FLOATING SIGNAL SOURCE - Suggested way to connect signals
and cable shield. Connection is made to Earth ground through
power ground.
Instrument
Shielded Cable
Signal High
Signal Low
Tie Low to GND
GND
GROUNDED SIGNAL SOURCE - Suggested way to connect
signal and cable shield. Ground is completed through
power ground. Voltage between outlet grounds not to
exceed the common mode range.
Figure 3-2. Recommended Cabling Method
Shielded
CIO-DAS16/M1/16
Cable
Channel # High
Channel # Low
10K
Figure 3-3. Recommended Method for Connecting Floating Signals
CIO-DAS16/M1/16
Channel # High
Channel # Low
LLGND
4
LLGND