Navigation
Rating 
Thanks 5
| 6/11/2009 8:18 PM | |
|
Posts: 12 Rating:
|
Hi, I'm a bit confused about the 2 wire connection on an AM2 analogue module. Both the documentation in the Logo! manual and on this site tell to connect the ground of the sensor to the M1 terminal. On the drawing however, the M wire is connected to the M terminal and no sign of the ground wire. The page https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=en&objid=23425009&caller=viewseems even to suggest that the PE and the M should be connected, which happens to work fine, but it isn't clear if this is the way to do it. The drawing shows a connection of the shield to the PE terminal - but then where does the ground go? If we follow these guidelines, the ground and the M end up connected witheachotherand the sensor ends up not-grounded. Thanks in advance for your comments. Best regards, Dimitri |
| 6/16/2009 2:15 PM | |
|
Posts: 12 Rating:
|
And thanks for your answer again Still the question remains: But why not just connect the ground of the sensor to the ground/PE of the system? (and not on the M) |
| 6/16/2009 5:42 PM | |
|
Posts: 173 Rating:
|
You CAN connect the ground of the sensor to the PE of the entire system - it will still work, BUT it is not good electrical engineering practice. If you want to do this, then the circuit of the sensor connected to the LOGO! is trying togo through the power supply. The Siemens LOGO! Power power supplies are isolated power supplies and you do not have to connect a PE to the supply because it is completely enclosed in plastic. You only need to connect the L1 & N and then you will get the 24 V DC L+ and M. If you are using such an isolated power supply and you connect a sensor to an AM2 module of the LOGO! with the sensor signal wire to the I1 or V1 input of the AM2 module and the negative/ground wire of the sensor connected to PE, then the circuit between PE and M has to be connected somewhere for the AM2 module to get an electrical signal from the sensor. If you connect the PE on the AM2 module to the M of the AM2 module and also to the M of the power supply, then you have made everything at the same ground potential and it will work, but then you have also made many more opportunities for ground loops between PE & M. Keeping the PE grounding separate from the M grounding will make sure that all the functional devices (LOGO! and sensors) are working on the SAME 'ground potential', so a 5V signal at one point (for example on a 0..10 V input) will have the same 0V reference voltage to another signal at another point. If you have some parts of the system referenced to PE as the signal ground and other signals from sensors somewhere else referenced to some other ground, then you will get some very strange readings or values that you do not expect. I will best try and explain it again with a diagram - please see the attached. AttachmentPE_ground_vs_Signal_ground.zip (577 Downloads) |
Last edited by: LOGO!Barbarian at: 6/16/2009 5:51 PM |
|
This contribution was helpful to
|
|
| 6/17/2009 1:59 PM | |
|
Posts: 153 Rating:
|
The pages from manual. AttachmentInstalation_and_wiring_LOGO!AM2_str.zip (1696 Downloads) |
Last edited by: Andrey [Str] at: 6/17/2009 2:04 PM |
|
Follow us on