Chapter 4
Connecting Signals
4-40
ni.com
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 6013/6014. Figure 4-35 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
device frequency generator 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 accuracy of measurements
made with the device 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 CH+ and
CH– 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 computer-based DAQ
system is the video monitor. Separate the monitor from the analog
signals as much as possible.
•
Separate device signal lines from high-current or high-voltage lines.
These lines can induce currents in or voltages on the device signal lines
if they run in parallel paths at a close distance. To reduce the magnetic
coupling between lines, separate them by a reasonable distance if they
run in parallel, or run the lines at right angles to each other.
