Chapter 3
Connecting the Signals
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National Instruments Corporation
3-43
DAQPad-MIO-16XE-50 User Manual
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
DAQPad-MIO-16XE-50. Figure 3-34 shows the OUT signal referenced to
the rising edge of a source signal. Any OUT signal state changes occur
within 80 ns after the source signal rising or falling edge.
FREQ_OUT Signal
This signal is available only as an output on FREQ_OUT. The FREQ_OUT
signal is the output of the DAQPad-MIO-16XE-50 frequency generator.
The frequency generator is a 4-bit counter that can divide its input clock
by 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 DAQPad-MIO-16XE-50 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.
You can 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 DAQPad-TB-52. 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 board carefully. Keep cabling away from noise
sources. The most common noise source in a PC DAQ system is the
video monitor. Separate the monitor from the analog signals as much
as possible.