Chapter 4
Connecting the Signals
4-44
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at that source edge, as shown by t
gsu
and t
gh
in Figure 4-39. The gate signal
is not required to be held after the active edge of the source signal.
If you use an internal timebase clock, the gate signal cannot be
synchronized with the clock. In this case, gates applied close to a source
edge take effect either on that source edge or on the next one. This
arrangement results in an uncertainty of one source clock period with
respect to unsynchronized gating sources.
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 6052E. Figure 4-39 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, generated by the NI 6052E frequency generator, is available
only as an output on 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 configurable from
the internal 10 MHz and 100 kHz timebases. The output polarity is
software configurable. This output is set to high-impedance at startup.
Field Wiring Considerations
Environmental noise can seriously affect the accuracy of measurements
if you do not take proper care when running signal wires between signal
sources and the device.
The following recommendations mainly apply to AI signal routing to the
device, although they also apply to signal routing in general:
•
Use differential input 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 far as possible.
