Hi guys,

I am still rookie with SIMATIC PLC handling. My problem is the following one - I connected one AI module (SM1231 AI 8x13 bit) to my CPU and set the first 2 channels as current inputs (4-20 mA). The problem is that both my probes (first one for T, second one for H) are passive and therefore I got no current through the loops. Do I need to add an external power supply into each loop or there is workaround solution? I am enclosing some screenshots for providing more information. Thanks in advance for any advice.

Regards,

Primoz

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Split from 4-20mA sensor in AI module.

Hi mapSO4,

I`ve got 2-wire sensors connected this way:

Sensor#1 - one wire to pin 0+, another one to 0-.

Sensor#2 - one wire to pin 1+, another one to 1-.

Values 65535 were my mistake and I already corrected them to 32767. 

Regards,

Banci

Hi 0_Einstein,

I did according to the manual and the scheme attached (see screenshot 4AI_Wiring).

Can you please check whether I miss something (have a look at screenshots Wiring2PLC and Wiring2probe)? I select the 4th channel at module, the brown wire is the power supply (+24VDC), the blue wire is GND and the white one is the probe return. I also checked the voltage at probe`s terminals and it`s below 5 V, far to low I think. Is it possible that I ruined something at module? The TIA portal reads the input current signal as 32676 value (see the screenshots TIA - Screenshot#1 and TIA - Screenshot#2). Btw - with V-type channels (+/-10V) I don`t have any problems.

Thanks in advance for any tip.

Regards,

banci

Hi banci,

Did you verify that the current is flowing through your circuit i.e. your transducer is giving 4-20 mA to the input card. For that purpose connect the probes of the a DMM in the series of the circuit and then check the current flow which will be like open the white cable coming from the transducer and connect it to the positive probe of the DMM and connect the negative probe of the DMM to the positive terminal of the module.

Hi Kashir,

I don`t know what went wrong but when I checked the current I got 11 mA and something, which was ok. Maybe I didin`t fix the terminal contacts enough. Now everything is fine, thanks.

There is only one thing that still bothers me - when I make on open circuit I get a readable input value above 27648. It supposed to be zero, doesn`t it?

Regards,

banci