Siemens S7-300 Manual page 23

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2.3

Measuring methods and measuring ranges of the SM 331;

AI 8

Measuring Methods

You can set the following measuring methods for the input channels:

S Voltage measurement

S Current 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

you obtain an optimum interference immunity for the analog input module. Set the

"measuring method" parameter for unused channels to "disabled".

Special characteristics of unused channels for some measuring ranges

Since configured inputs can remain unused because of the channel group

generation, you must take note of the following special characteristics of these

inputs to enable the diagnostic functions on the used channels.

S Measuring range 1 to 5 V: parallel connection of the unused input with the

used input of the same channel group.

S Current measurement, 2-wire transmitter:

two channel wiring options.

a) Leave the unused input open and do not enable diagnostics for this

channel group. Otherwise, if diagnostics are enabled, the analog

module triggers a single diagnostic interrupt and the SF LED of the

analog module comes on.

b) Connect the unused input with a resistance of 1.5 to 3.3 kW. You may

then enable diagnostics for this channel group.

S Current measurement 4 to 20 mA, 4-wire transmitter: series connection of

the unused input with the input of the same channel group.

Product Information on the Manual S7-300 Module Specifications, Edition 11/2002

A5E00213444-02

14 Bit High Speed

. In this way,

ANA

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