User manual

Chapter 4 Connecting Signals

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 6034E/6035E/6036E device. 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 tri-state at

startup.

Field Wiring Considerations

Environmental noise can seriously affect the accuracy of measurements

made with your device if you do not take proper care when running signal

wires between signal sources and the device. The following

recommendations apply mainly to analog input 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 analog input connections to reject common-mode

noise.

• Use individually shielded, twisted-pair wires to connect analog input

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 data

acquisition system is the video monitor. Separate the monitor from the

analog signals as much as possible.

UM.book Page 41 Monday, May 14, 2001 10:32 AM