Measurement Computing ADAC/5500 Series - Manual (Page 20)

ADAC Series PCI Boards 795 - 15 - ADAC/5500 Series User Manual
Signal Level
In addition to the grounding of source signals, the maximum voltage level of the signal should be taken into account
when choosing the optimum input configuration on the data acquisition board. When working with signals with a
maximum level below 1 V (Low Level), care must be taken to minimize possible affects caused by noise in the
environment. The addition of noise will have less effect on signals in the 1-10 V range (High Level), and therefore
High Level signals can use more types of input configurations.
4.1.2 Choosing A/D Input Configuration
Once you have determined what type of input signal source you have, and the voltage level, you then need to select the
proper/optimum input configuration on your data acquisition card:
4.1.2.1 Single-Ended
Applications with a Floating Source are typically wired to a data acquisition board configured for Single-
Ended (SE) configuration. Since only one wire from each input signal is connected to a multiplexed input of
the A/D, the Single-Ended configuration provides a larger number of inputs per board than Differential (see
below) configuration. Grounded Signal Sources can be wired in Single-Ended configuration only when signal
leads are less than 12 feet AND when all signals share a common ground (the signals must be local to one
another).
With the Single-Ended configuration, the input signals are tied to the Channel Hi side of an analog input, and
all signal low sides are tied to the SGND ground on the data acquisition card.
Single-Ended configuration should only be used when:
• There is no Common Mode Voltage
• Ground isolation is not required
• Signal leads are less than 12 feet.
Note that of all the three possible input configurations, Single-Ended offers the least amount of noise rejection.
Because of this, Low Level signals should only be wired in Single-Ended configuration when you are certain
that there is little or no noise being introduced to the signal from the system, or the environment. We DO NOT
recommend using Single-Ended configuration with Low Level signals.
Figure 4.1 shows proper wiring for Single-Ended configuration.
Figure 4.1
Single-Ended Configuration
928