User Manual
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Siemens TX-I/O Engineering and installation guide CM110562en_13
Building Technologies Principles of electrical design 2019-05-15
10.11 Digital inputs (status and counting)
The permissible length of the cables connected to the status contacts and counter
contacts, regardless of the thickness of the wire (min. diameter 0.6 mm) is restricted to
300 m and is defined by the anticipated noise interference.
Counter inputs faster than 1 Hz that are routed for more than 10 m in the same trunking
as analog inputs must be shielded.
When several status or counter contacts are to be connected, a common ⊥ conductor
may be used. This saves wiring.
However, system ground must be connected at least once per module (see 6.6).
1 3 52 4 6
U1
7 8 9 10
10562A030
(1) (2) (3) (4) (5)
In principle, the number of contacts that can be connected via a common ⊥ conductor
depends on the length and cross section of the conductor.
However, the measuring current (1 … 1.6 mA) is so small that all 16 inputs of a
TXM1.16D module can be connected with the minimum cross section 0.28 mm
2
(0.6 mm diameter) and with the maximum cable length of 300 m.
Technical data
Digital inputs /
counter inputs
Digital inputs are not electrically isolated from the system electronics.
Mechanical contacts must be volt-free.
Electronic switches must comply with SELV or PELV standards.
Contact sensing voltage
DC 21.5 ...25 V
Contact sensing current (TX1.8X, 8U)
1.0 mA (initial current 6 mA)
Contact sensing current (TX1.8D, 16D)
1.6 mA (initial current 10 mA)
Insulation resistance with
contacts closed
Max. 200Ω
Contact resistance with contacts open
Min. 50kΩ
A = TXM1.8D, 16D
B = TXM1.8U, 8U-ML,
TXM1.8X, 8X-ML
Min. closing /
opening time [ms]
including bouncing
Max. bounce time
[ms]
Max. counting
frequency
(symmetric)
A B A B A B
Maintained contact
80
60
40
20
Pulse contact
50
30
30
10
Counter mechanical
1)
40
20
30
10
10 Hz
25 Hz
Counter electronic
2)
5
0
10 Hz
100 Hz
Counter inputs
counter memory
0 ... 4.3 x 10
9
(32 bit counter)
1) TXM1.16D: I/O points 1 ... 8 only
Cable length
STOP
Counter inputs
Common ⊥
conductor
with multiple contacts
Connection diagram
(Example)