National Instruments NI PCI-6110 - Manual (Page 67)

Chapter 4 Connecting Signals
© National Instruments Corporation 4-37 NI PCI-6110/6111 User Manual
The OUT output timing parameters are referenced to the signal at the
SOURCE input or to one of the internally generated clock signals on the
NI PCI-6110/6111. Figure 4-33 shows the OUT signal referenced to the
rising edge of a source signal. Any OUT signal state changes occur within
80 ns after the rising or falling edge of the source signal.
FREQ_OUT Signal
This signal is available only as an output on the FREQ_OUT pin.
The frequency generator for the NI PCI-6110/6111 outputs the
FREQ_OUT pin. The frequency generator is a 4-bit counter that can divide
its input clock by the numbers 1 through 16. The input clock of the
frequency generator is software-selectable from the internal 10 MHz and
100 kHz timebases. The output polarity is software-selectable. This output
is set to high-impedance at startup.
Field Wiring Considerations
Environmental noise can seriously affect the measurement accuracy of the
NI PCI-6110/6111 if you do not take proper care when running signal wires
between signal sources and the device. The following recommendations
apply mainly to AI signal routing to the device, although they also apply to
signal routing in general.
Minimize noise pickup and maximize measurement accuracy by taking the
following precautions:
• Use differential AI connections to reject common-mode noise.
• Use individually shielded, twisted-pair wires to connect AI signals to
the device. With this type of wire, the signals attached to the ACH+ and
ACH– inputs are twisted together and then covered with a shield. You
then connect this shield only at one point to the signal source ground.
This kind of connection is required for signals traveling through areas
with large magnetic fields or high electromagnetic interference.
• Route signals to the device carefully. Keep cabling away from noise
sources. The most common noise source in a PCI DAQ system is the
video monitor. Separate the monitor from the analog signals as far as
possible.
• Separate the NI PCI-6110/6111 signal lines from high-current or
high-voltage lines. These lines can induce currents in or voltages on
the NI PCI-6110/6111 signal lines if they run in parallel paths at a
close distance. To reduce the magnetic coupling between lines,