"Mein Mikrocontroller (Mesakarte) hat im Ruhezustand (nicht geschaltet) 24VDC am Pin anliegen."
Dann hat die Mesa einen Pull-Up Widerstand drin, welcher die Spannung auf 24V rauf zieht, wenn der Eingang unbeschaltet bzw Schalter offen ist.
Der Schalter ist dann also eingangsseitig an Ground angeschlossen. Richtig?
Ja genau, das Gegenstück auf der Mesakarte ist an GND angeschlossen.
Zitat aus dem Handbuch, Version 1.5
ISOLATED INPUT CHARACTERISTICS
The isolated inputs use opto-isolators with a 4.7K input series resistance. This
results in an approximate current draw of 5 mA at 24V. The inputs will operate with +-4V
to +-36V signals relative to input common. Isolated inputs are relatively slow and not suited
for signals faster than about 5 KHz. Each input pair has a separate common connection
to allow mixing of sinking/sourcing and mixed supply voltages.
For PNP type sensors or switches with a common positive, the input common pin
for a given input pair is grounded.
For NPN type sensors or switches with a common ground, the input common for a
given input pair is connected to +5 to +36V and the input pins are grounded to activate an
input.
