Analog Modules
4-122
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Special characteristic of channel groups with resistance measurement
If you use the resistance measurement method, there is only one channel per
channel group. The “2nd” channel of each group is used for current injection (I
C
).
The measured value is obtained by accessing the “1st” channel of the group. The
“2nd” channel of the group has the default carry value “7FFF
H
”.
Special characteristic of channel groups for hardware interrupts
You can set hardware interrupts in STEP 7 for the channel groups 0 and 1. Note,
however, that a hardware interrupt is set only for the first channel in the channel
group in each case – in other words, for channel 0 or channel 2
Diagnostics
You will find the diagnostic messages that are grouped under the “group diagnosis”
parameter in Table 4-46, on page 4-72.
4.22.2 Measuring Methods and Measuring Ranges of the SM 331;
AI 8 x 12 bits
Measuring Methods
You can set the following measuring methods for the input channels:
• Voltage measurement
• Current measurement
• Resistance test
• Temperature measurement
You perform the setting by means of the measuring range modules on the module
and with the “measuring method” parameter in STEP 7.
Unused Channels
You must short-circuit unused channels and connect them to M
ANA
. In this way,
you obtain an optimum interference immunity for the analog input module. Set the
“measuring method” parameter for unused channels to “disabled”. In this way you
shorten the scan time of the module.
If you do not use the COMP input, you must short-circuit it also.
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