DL205 Analog I/O Manual, 7th Edition Rev. D
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Chapter 1: Getting Started
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Analog Input Module Terminology
Several different terms are used throughout the rest of this manual. The terms may be helpful
to make it easier to select the appropriate analog modules. Take a few minutes to review these
definitions.
Channels per Module - The total number of analog signals the module receives from field
devices.
Input Ranges - The minimum to maximum spans in voltage or current the module will
successfully convert to digital values.
Resolution - The number of binary weighted bits available on the digital side of the module for
use in converting the analog value to a digital value.
Input Type - Specifies if the module accepts single ended, or differential input signals.
Input Impedance - The resistive load of the module as seen by a voltage or current input signal.
Conversion Method - The method the module uses to convert the analog signal to a digital
value.
PLC Update Rate - Speed at which the analog signals are digitized and acknowledged in the
PLC.
Linearity Error - The relative accuracy of the digital representation over the entire input range.
Maximum Inaccuracy - Maximum absolute error of the digital representation of the signal
over the entire input range. Factors which contribute to maximum inaccuracy are also specified
separately. These factors are full-scale calibration error, offset calibration error, and accuracy
vs. temperature.
Accuracy vs. Temperature - The variations in the module’s conversion accuracy with
temperature over the module’s operating temperature range.
I/O Points Required - The number of I/O points the CPU must dedicate to the module.
External Power Source - Some modules require a separate 12VDC or 24VDC power source.
The 24VDC output supply at the local base can be used as long as you do not exceed the
current ratings of 300mA.
Base Power Required - The amount of base current required by the module. Use this value in
your power budget calculations.
Operating Temperature - The minimum and maximum temperatures the module will operate
within.
Relative Temperature - The minimum and maximum humidity the module will operate
within.
Step Response - The time required for an analog input to reach 95% of its final value at the
converter following a step change in the input signal level.
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