Nematron Pointe Controller - Manual (Page 93)

Pointe Controller User Guide Chapter 4: System Design and Installation
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Accuracy
Accuracy is expressed as the worst case deviation from the “ideal value” across
the entire input range. For example, for a 0 to 5V input range and a 12-bit A/D
module, a 2.0 volt input should yield a value equal to 1638 (0.4 x 4096). If it
returns a value of 1636, and this is the worst case error across the entire range of
0 to 5V, the accuracy is 12 bits +/- 2 counts.
Range
The analog input range is the minimum and maximum voltage, or current level,
measured by the A/C converter. Typical ranges are 0 to 5 volts, 0 to 10 volts, +/- 5
volts, +/- 10 volts, and 4 to 20 mA.
You should try to match the input range to the range of the signal that you are
measuring.
Multiplexing
Analog to digital converter devices are typically quite expensive. In order to keep
the cost per channel of analog inputs down, a multiplexer is commonly used.
A multiplexer switches one analog input at a time into the A/D converter. Each
input is converted in sequence. The trade off is reduced sampling rate for a
particular channel versus reduced cost per channel measured. In most industrial
applications, the conversion rate is so fast in relation to the rate of change in the
measured value, that sampling rate is not a factor.
Single Ended Inputs
Single ended inputs are all referenced to the same ground point. In many
applications, single ended inputs produce significant advantages. Single ended
inputs require only one ground connection and one signal input per measured
value. The result is reduced wiring costs along with the reduced cost per channel
on the analog input module.