Signal Connections
Chapter 3
DAQCard-700 User Manual
3-4
© National Instruments Corporation
The connector pins can be grouped into analog input signal pins, digital I/O signal pins, and
timing I/O signal pins. Signal connection guidelines for each of these groups are included in the
following pages.
Analog Input Signal Connections
Pins 1 through 18 are analog input signal pins for the ADC. Pins 1 and 2, AIGND, are an analog
common signal. You can use these pins for a general analog power ground tie to the
DAQCard-700. Pins 3 through 18 are the ACH<15..0> signal pins. These pins are tied to the
analog input channels of the DAQCard-700 through 4.7 k
Ω
series resistors. These resistors limit
the input current to the multiplexer. The following input ranges and maximum ratings apply to
inputs ACH<0..15>:
•
Input signal range
±
2.5 V,
±
5 V, or
±
10 V
•
Maximum input voltage rating
±
30 V powered on or off
Warning: Exceeding the input signal range distorts input signals. Exceeding the maximum
input voltage rating may damage the DAQCard-700 card and the computer.
National Instruments is
NOT
liable for any damages resulting from any such signal
connections.
Types of Signal Sources
When configuring the input mode of the DAQCard-700 and making signal connections, you
should first determine whether the signal source and the measurement system are floating or
ground referenced. The two types of signal sources are described as follows, and the types of
measurement systems are described in later sections.
Ground-Referenced Signal Sources
A ground-referenced signal source is one that is connected in some way to the building system
ground. Nonisolated outputs of instruments and devices that plug into the building power system
fall into this category.
The difference in ground potential between two instruments connected to the same building
power system is typically between 1 and 100 mV but can be much higher if power distribution
circuits are not properly connected. The connection instructions described later in this chapter
for grounded signal sources are designed to eliminate this ground potential difference from the
measured signal.
Floating Signal Sources
A floating signal source is one that is not connected in any way to the building ground system
but rather has an isolated ground-reference point. Some examples of floating signal sources are
outputs of transformers, thermocouples, battery-powered devices, optical isolator outputs, and