VL-1225/6 Analog Input/Output Board
2-13
Analog Input Configuration
The VL-1225/6 board accommodates 16 single-ended or 8 differential channels.
Input Mode
The VL-1225/6 board can be configured for three types of voltage inputs: differential, single-ended, and
pseudo-differential. In addition, by adding an external user-supplied 500
W
resistor, the VL-1225/6 can be
hooked up to a 4-20 ma current loop. All inputs connected to the boards must be of the same type.
Typical connections for the three input modes are shown in the figures below. Since ground loops (current
flowing between various equipment ground lines) affect analog measurements made with reference to
ground, careful attention should be paid to the ground connections shown. In particular, the STD Bus
power supply logic ground line should never be connected to earth ground when operating in the
differential or pseudo-differential modes.
Single Ended Mode
The single-ended mode is used for signals that are referenced to a common ground. It is normally used
only for higher level signals on short distance runs (less than 10 feet). In this mode up to 16 input channels
can be accommodated.
Figure 2-11. Single Ended Input Mode
Configuration – Analog Input Configuration
