Current; Switch; Grounding - Siemens SIMATIC S7-300 Manual

Power supply
You must connect the interval counter input to a 20 V power supply. It is recommended to
use the 24 V load voltage supply.

Current

The current flow on a signal line with '1' state (connected to + 24 V) must have a minimum
value of 2.5 mA and a maximum of 4.4 mA.
You must observe this minimum current to make allowances for a certain voltage drop, for
example, if using an electronic proximity switch switch instead of the mechanical, low-
bounce switch shown in the drawing above. You'll have to observe the maximum current if
compensating for this voltage drop with a voltage higher than 24 V.
Cables
Always used shielded, twisted-pair cables. Interconnect the cable shield with the grounded
rack via the shield connection element similar to the other analog cables.

Switch

The switch of the cam disc must be capable of operating at an opening and closing ratio of 1
ms at the highest speed.

Grounding

The interval counter input is electrically isolated from all other terminals to prevent the
generation of ground loops.
To provide a reference potential for the interval counter input, it is sufficient to connect the
input to the 24 V load voltage which is connected to ground potential; refer to the SIMATIC
S7-300, Hardware and Installation
(http://support.automation.siemens.com/WW/view/en/13008499) Operating Instructions.
SM 335 - High-speed analog mixed module for SIMATIC S7-300
Manual, 02/2009, A5E02409063-01
Interval counter input
4.3 Wiring the interval counter input
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