Analog Input and weather station modules

[IC_Systems]

Hello Dears,

I have two modules (Analog input MTN682191 and Weather station MTN682991) as analog input all inputs are 4-20mA, 

both modules and sensors connected to the same 24V DC Power supply.

I noticed that the reading from the Weather station module are incorrect, I refereed to the manual and its mentioned that "US and GND must not be interconnected with the corresponding terminals of another device." 

So To be sure I need a power supply for each module? and why?

[Thomas_Rohde]

Hello IC_Systems,

I do not understand fully this sentence:
"... both modules and sensors connected to the same 24V DC Power supply."

1. The article MTN682191 needs to be powered with AC 24V and not DC. Maybe it was just a typo?!

2. Did you connected +Us/GND of both modules also?

[IC_Systems]

Hello @Thomas_Rohde 

regarding: 2. Did you connected +Us/GND of both modules also? Yes

I have one DC Power supply connected to the +US/Gnd for both Analog input and Weather station modules.

but When I replace the Weather station module with Analog Input module and keep the +US/Gnd Connected for the both modules, the issue solved and the values become reasonable.

Is the issue connecting the +US/Gnd for Analog input and weather station, but if connecting same modules there will be no issue?

I am referring to this quotation from the manual : "Never connect the sensors at the inputs (K1...K4) of the weather station to the supply terminals US and GND of a connected analog input module. US and GND must not be interconnected with the corresponding terminals of another device."

[Thomas_Rohde · Accepted solution]

Hello IC-Systems,
out of your answer I see that you have connected the 24V DC to contacts +US/GND and these you have even linked them between the weather station and the analogue input.
But there is no need to connect 24V DC to +US/GND. The devices are powered (beside KNX) with 24V AC. This is used to provide a certain voltage/current +US/GND by THEM SELVES.
If you connect 24V DC in addition (which is by the way not described or requested in the manual) then this influences the results of the voltage/current of the inputs and you will get bad results on the KNX-Side. 
Connecting even both modules will influence the internal measurement also in a bad way.

I propose to wire them completely seperat as shown in the picture.

[IC_Systems]

thanks @Thomas_Rohde 

So there is no need for external 24V DC unless the consumption current exceeds 100mA.

But I have this scheme in the site and its working fine and the readings are reasonable, Is there any issue in this scheme?

 

[Thomas_Rohde]

to "So there is no need for external 24V DC unless the consumption current exceeds 100mA."
Yes correct.

to "But I have this scheme in the site and its working fine and the readings are reasonable, Is there any issue in this scheme?"
As you already wrote ... "the readings are reasonable," But I think you can improve the figures by deleting the bridge and 24V. Finally it is up to you ... I can just propose 😉