Hardware Filter 8 Channels Scan Time - Siemens SIMATIC S7-300 Reference Manual
Programmable logic controllers module data
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Analog Modules
"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).
Figure 4-42
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
Scan time = (85 ms + 12 ms) x 2
Scan time = 194 ms
t
:
channel conversion time for one channel
K
t
:
time for switching to the other channel in the channel group
U
4-132
Start analog conversion
(simultaneous)
K0
K2
Start analog conversion
(simultaneous)
K1
K3
Hardware filter 8 channels scan time
+ t
) x 2
K
U
K4
K6
K5
K7
Programmable Logic Controllers S7-300 Module Data
Scan time
A5E00105505-03
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