Current Or Voltage Input; Choosing Resistors - Siemens SIMATIC 505 PPX:505–6108A User Manual

Analog Input Operation (continued)
Current or Voltage
Input

Choosing Resistors

1-6 Product Overview
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
The analog input module has eight inputs. You can select each of the eight
inputs to receive either voltage or current as the incoming analog signal.
Since the inputs are single-ended, the source for a current signal must be a
true current-sourcing transmitter, not a current-sinking transmitter.
For a voltage input, the incoming signal may range from –5 to +5 V, or
from –10 to +10 V. The optional voltage input range of 10 V is available
via jumper selection on the circuit board. The voltage range selected
applies to all eight input channels. Refer to Figure 3-2.
For a current input, the incoming signal may range from 0 to 20 mA.
NOTE: The module is factory-calibrated and shipped configured for the 5 V
input range, which is required for current input using the internal sense
resistors. If your application requires 10 V, recalibrate the module with the
10 V setting selected.
The input module has eight (one per point) built-in, precision resistors
(250 Ω, 0.1%). The resistor changes input current to voltage, which is what
the module monitors internally. The built-in resistor allows a current range
from 0 to 20 mA. You may use other external resistor values for other
current ranges. If you install an external resistor, be sure that it meets the
5 V input constraint and connects between Voltage In and Return for the
selected channel. Follow proper safety guidelines when you install resistors.
To determine the resistor needed, use the following equation.
Resistor needed (W) +
5 V
max current in amps
Series 505 Analog I/O Modules User Manual