Measurement Computing CIO-DAS801 - Manual (Page 15)

15
Chapter 3
Functional Details
Analog inputs
Analog inputs on the CIO-DAS801 are designed to accept voltage signals for measurement.
The analog inputs may be configured in three different ways:
 True differential inputs; for sources with a separate ground, common to the PC.
 Pseudo-differential inputs used for floating sources has noise rejection capability
 Single ended inputs; also used for floating sources.
Caution! Using a voltmeter, measure the AC and DC voltage between the ground signal at the signal source
and the PC. 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-DAS801 to this signal source because you
will not be able to make any reading. If there is more than 30 volts, DO NOT connect this signal
to the board because it will damage the board and possibly the computer.
Use great care when measuring any voltage. Voltages over 30 V can be dangerous to your health.
Single-ended inputs
A single ended input is two wires connected to the CIO-DAS801; a channel high (CH# HI) and a Low level
ground (LLGND). The LLGND signal must be the same ground the PC is on. The CH# HI is the signal
voltage. Single-ended mode is selected via switch S2 on the board (refer to Input configuration on page 10 for
more information.)
Floating differential
A floating differential input is two wires from the signal source and a 10K ground reference resistor installed at
the CIO-DAS801 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 CIO-DAS801 CH# LO and LLGND pins. This is
accomplished with the installation of the SIP resistor pack.
A floating differential hookup is handy when the signal source is floating with respect to ground, such as a
battery, 4-20 mA transmitter or if the lead lengths are long or subject to EMI interference. The floating
differential input will reject up to 10 V of EMI on the signal wires.
Caution! Verify that the signal source really floating. Check it with an ohmmeter before risking the CIO-
DAS801 and the PC.
Fully differential
A differential signal has three wires from the signal source. The signals are Signal High (CH# HI), Signal Low
(CH# LO) and Signal Ground (LLGND).
A differential connection allows you to connect the CIO-DAS801 to a signal source with a ground that is
different than the PC ground, but less than 10 V difference, and still make a true measurement of the signal
between CH# HI and CH# LO.
Example: A laboratory instrument with its own wall plug. There are sometimes voltage differences in wall
GND between outlets.