sm331

 Hello behrooz;

There are many points you must pay attention to when using an analog input module, you must check them all, systematically, if you want to read an analog sensor from the field.

- First, which analog input module are you using? This manual will give you the complete list of the most recent modules in the section "Analog modules":

https://support.industry.siemens.com/cs/us/en/view/8859629

Attached below is a screenshot from the chapter on analog modules listing the part numbers from the manual.

behrooz_mb

hi

i have a sm331 analog input current on s7 300 

the inputs are ok (tested by source) and the module has been replaced

but we havent any number in the plc

how can i solve it?

 - Once you have found the part number of your module, look at the type of signals it supports (current 2-wire, current 4-wire, voltage, temperature...). Validate that the sensor you are using produces the type of signal supported by your analog input module.

- Now go to the section for your module, showing the different wiring diagrams for each type of signal. Generally each diagram is given for only one channel, if there are more channels used you must visualize and draw the wiring for each channel so you can check that ir has been done properly.

- Also check whether your particular module uses the Mana pin in your wiring, verify that it has been done properly. Verify how your module treats unused channels, do they need to be wired in a special way, do you have to do settings in the module properties (in HWConfig)?

- Open the HWConfig editor and check what input addresses have been attributed to your module. Let's say you are using a 2-channel analog input module, you would see a range of addresses something like 256..259. Analog signals are treated by the PLC differently that digital signals. They are considered "peripheral" addresses (outside of the Input Image Table, where digital inputs are treated) and when used in your program the channels must be addressed as PIW 256 and PIW 258.

- Once you are at this point and if everything has been configured and wired properly, you should have values in your channel addresses.You cannot see them in a VAT table, if you want to monitor them transfer them to a M-word address. At this point you can decide to scale the raw values of these channels to engineering values, using FC 105 from the TI-S7 converting library.

Hope this helps,

Daniel Chartier