4-Channel Mode - Siemens SIMATIC S7-300 Reference Manual
Programmable logic controllers module data
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Scan time of the module
In the 8-channel mode of the SM 331; AI 8 x 16 bits, the channel conversion time
depends on the selected interference frequency. When you set an interference
frequency of 50 Hz, the channel conversion time including communication time is
76 ms. When you set an interference frequency of 60 Hz, the channel conversion
time is 65 ms. When you set an interference frequency of 400 Hz, the channel
conversion time is reduced to 16 ms. When you set an interference frequency of
50, 60 and 400 Hz, the channel conversion time is 88 ms. The module must then
be switched over to the other channel of the group by means of opto-MOS relays.
Opto-MOS relays need 7 ms to switch and settle. Table 4-56 shows the scan times
of the module at certain interference frequencies.
Table 4-56 Scan times in 8-channel mode
Interference frequency
400/60/50
4.19.3
4-channel mode
Description of the module cycle
In 4-channel mode, the SM 331; AI 8 x 16 bits does not switch over between the
channels of the individual groups. As the module contains four analog/digital
converters (ADC), all four of the ADCs convert simultaneously for channels 0, 2, 4
and 6.
Figure 4-36
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Channel scan time
(Hz)
50
60
400
Start analog conversion
(simultaneous)
K0
K2
4-channel mode cycle
Module scan time
(ms)
83
72
23
95
K4
K6
Analog Modules
(All channels)
166
144
46
190
Scan time
4-93
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