A SECU16 input looks like this:
Code:
+5v
|
1k res.
|
supervised
mode jumper
| Analog
input >--+---------mux chip-------->PIC analog input
|
current loop
mode jumper
|
249 ohm res.
|
common >+------------------------->common
In supervised mode, it pulls up the input signal to +5v through 1k, while in analog mode it just passes through the analog mux chip (CMOS 14051). In current loop mode, the input is pulled to common through a 249 ohm precision resistor to convert a 4 to 20mA signal into a 1 to 5v signal.
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