Analog Modules
4-132
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
”Hardware filter 8 channels” mode
In “Hardware filter 8 channels” mode, the analog input module SM331; AI 8 x RTD
switches over between the two channels in each group. As the module contains
four analog/digital converters (ADC), all four of the ADCs convert simultaneously
for channels 0, 2, 4 and 6. Once the even-numbered channels have been
converted all the ADCs simultaneously convert for the odd-numbered channels 1,
3, 5 and 7 (see Figure 4-42).
Scan time
Start analog conversion
(simultaneous)
K0 K2 K4 K6
K1 K3 K5 K7
Start analog conversion
(simultaneous)
Figure 4-42 Hardware filter 8 channels scan time
Scan time of the module
In 8-channel hardware filter mode, the channel conversion time including the
communication time of the analog input module SM 331; AI 8 x RTD is 85 ms. The
module must then be switched over to the other channel in the group by means of
opto-MOS relays. Opto-MOS relays need 12 ms to switch and settle. Each
channel needs a time of 97 ms, so that the scan time is exactly 194 ms.
Scan time = (t
K
+ t
U
) x 2
Scan time = (85 ms + 12 ms) x 2
Scan time = 194 ms
t
K
: channel conversion time for one channel
t
U
: time for switching to the other channel in the channel group
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