Calculating The Counter Frequency Limit - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
11.6

Calculating the Counter Frequency Limit

The maximum counting frequency (frequency limit) - without connecting programmers, OPs, SINEC
L1/L2 is as follows:
S5-90U: 1 kHz
S5-95U: 5 kHz for counter A, 2 kHz for counter B,
5 kHz for counter cascade.
If you want to use the PLC interfaces (e.g. connect an OP to the programmer interface), you can
calculate the maximum counting frequency (frequency limit) of the counters by means of simple
formulae:
S5-90U
For counter: Frequency limit 1 kHz.
Frequency limit =
S5-95U
For counter A or counter cascade:
Currently valid
Frequency limit =
comparison value of counter A
For counter B: Frequency limit 2 kHz.
Frequency limit =
0.5 ms + additional interrupt reaction time
Example: An OP is connected to the programmer interface of the S5-95U. The currently valid
comparison value is 3 for counter A. The frequency limits for counters A and B are to
be calculated.
According to Table 10-6 in Section 10.4, the additional interrupt reaction time for the OP
function is 0.4 ms.
Counter A:
Frequency limit=
In the example, the frequency limit for counter A is 3.3 kHz.
Counter B:
Frequency limit=
In the example, the frequency limit for counter B is 1.1 kHz.
EWA 4NEB 812 6115-02b
1
1 ms + additional interrupt reaction time
*
See Section 10.4, Table 10-6 for additional reaction times
Frequency limit 5 kHz.
*
See Section 10.4, Table 10-6 for additional reaction times
1
*
See Section 10.4, Table 10-6 for additional reaction times
1
3
•
(0.5 ms + 0.4 ms)
1
= 1.111 kHz
(0.5 ms + 0.4)
Onboard Counter Inputs
*
1
•
(0.5 ms + additional interr. reaction time
*
= 3.33 kHz
)
*
11-9