Analog input signal connections, Analog output signal connections – National Instruments BNC -2140 User Manual
Page 16
Chapter 3
Signal Connections
© National Instruments Corporation
3-5
Caution
Connections that exceed any of the maximum ratings for input or output signals
on the BNC-2140 accessory can damage not only the BNC-2140 but also the DSA plug-in
device and the computer. Maximum input ratings for each signal are given in Appendix A,
. National Instruments is not liable for any damages resulting from signal
connections exceeding maximum ratings.
The outer shell of the BNC connectors is not GND (0 V). The outer shell
of the BNC is not physically connected to the metal box of the BNC-2140.
In DIFF mode, the outer shell is the inverting differential signal; in SE
mode, the outer shell is tethered to GND (0 V) through a 50
Ω, 1 W resistor.
Analog Input Signal Connections
The analog input signals for the BNC-2140 device are +ACH<0..3> and
–ACH<0..3>. How you connect analog input signals to your BNC-2140
accessory depends on the configuration of the input signal sources.
For most signals, you use a DIFF configuration and simply connect the
signal to +ACHx (where x is the BNC-2140 channel) and the signal ground
(or signal minus), as appropriate, to –ACHx. If a signal has a high output
impedance (greater than 1 k
Ω) and is floating, you may find it useful to use
an SE configuration that tethers the signal minus to AIGND. This reduces
common-mode interference.
Analog Output Signal Connections
The BNC-2140 analog output signals are +DAC0OUT, –DAC0OUT,
+DAC1OUT, and –DAC1OUT.
+DAC0OUT is the voltage output signal for analog output channel 0.
+DAC1OUT is the voltage output signal for analog output channel 1.
The way you connect analog output signals from your BNC-2140
accessory depends on the configuration of the devices receiving the signals.
For most signals, you use a DIFF configuration and simply connect
+DACxOUT (where x is the BNC-2140 channel) to the signal and
–DACxOUT to the signal ground (or signal minus), as appropriate. When
driving some devices with floating grounds, you may sometimes find it
helpful to use the SE configuration and connect the floating ground system
of the device to AOGND to reduce common-mode noise coupled from an
interfering source to the device.