Siemens SIMATIC S7-1200 - 5.7 Protecting access to the CPU or code block is easy

Installation
4.4 Wiring guidelines
S7-1200 Programmable controller
82 System Manual, V4.2, 09/2016, A5E02486680-AK
If you design your own suppressor circuit, the following table suggests resistor and capacitor
values for a range of AC loads. These values are based on calculations with ideal
component parameters. I rms in the table refers to the steady-state current of the load when
fully ON.
Table 4- 18 AC suppressor circuit resistor and capacitor values
Inductive load
Suppressor values
I rms
230 V AC
120 V AC
Resistor
Capacitor
Amps VA VA Ω W (power rating) nF
0.02
4.6
2.4
15000
0.1
15
0.05
11.5
6
5600
0.25
470
0.1
23
12
2700
0.5
100
0.2
46
24
1500
1
150
0.5
115
60
560
2.5
470
1
230
120
270
5
1000
2
460
240
150
10
1500
Conditions satisfied by the table values:
Maximum turn-off transition step < 500 V
Resistor peak voltage < 500 V
Capacitor peak voltage < 1250 V
Suppressor current < 8% of load current (50 Hz)
Suppressor current < 11% of load current (60 Hz)
Capacitor dV/dt < 2 V/μs
Capacitor pulse dissipation : ∫(dv/dt)
2
dt < 10000 V
2
/μs
Resonant frequency < 300 Hz
Resistor power for 2 Hz max switching frequency
Power factor of 0.3 assumed for typical inductive load
Guidelines for differential inputs and outputs
Differential inputs and outputs behave differently than standard inputs and outputs. There
are two pins per differential input and output. Determining whether a differential input or
output is on or off requires that you measure the voltage difference between these two pins.
See the detailed specifications for the CPU 1217C in Appendix A (Page 1425).