CIO-EXP16 User's Guide
Functional Details
Floating differential input
A floating differential input has two wires from the signal source, and a 100 K ground reference resistor
installed at the CIO-EXP16 input. The two signals from the signal source are Signal High (CH#-HI) and Signal
Low (CH#-LO). The reference resistor is connected between the CH#-LO and #-G (Signal Ground) pins.
Use a floating differential hookup when the signal source is floating with respect to ground, such as a battery, 4-
20 mA transmitter or thermocouple, and the lead lengths are long or subject to electromagnetic interference
(EMI) pickup.
A thermocouple is an example of a floating differential signal source. Instead of using an external 100 K
resistor, add a solder bridge between the 'G' pads to enable a ground reference. The floating differential input
will reject up to 10 V of EMI.
Caution!
Use a voltmeter to verify that the signal source is floating, or you may damage the CIO-EXP16
and/or your computer.
Differential input
A differential signal uses three wires from the signal source — Signal High (CH#-HI), Signal Low (CH#-LO)
and Signal Ground (#-G).
With a differential configuration, you can connect the CIO-EXP16 to a signal source with a ground that is
different from the PC ground, but with less than 10 V difference, and still make a true measurement of the
signal between CH# HI and CH# LO. An example of this is a laboratory instrument with its own wall plug,
where there are sometimes differences in wall grounds between outlets.
Information on signal connections
For general information about signal connection and configuration, refer to the
Guide to Signal Connections
on
our web site at
www.mccdaq.com/signals/signals.pdf
Thermocouples
A thermocouple is made of two dissimilar wires that react electrically when in contact with each other. The
reaction produces a voltage which is dependent on the temperature at the point where the two metals touch.
There is a reaction at every point where dissimilar metals (the thermocouple wire) touch, including the screw
terminal where the thermocouple wire is connected to the CIO-EXP16 board.
To process thermocouple signals, the CIO-EXP16 provides cold junction compensation (CJC), open
thermocouple detect (OTD) and stable amplification for accurate temperature measurements.
Figure 12
Figure 12. Typical thermocouple connection
shows a thermocouple connected to one channel of the CIO-EXP16. The thermocouple has a positive
and a negative lead. If you're not sure which is the positive lead and which is the negative lead, make a test
hookup and use a match to heat the thermocouple. If the temperature reading goes down, switch the leads.
C = Filter capacitor, pad open. V = Open TC Detect, pad open. G = Reference to ground, pad open.
Pads are located on the circuit side. All pads must be closed when thermocouples are used.
Thermocouple
negative lead
Thermocouple
positive lead
High
Low
Ground
Ground
Low
High
-15 V
3.9M
10K
10K
100K
1 F
µ
C
V
G
19
Summary of Contents for CIO-EXP16
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