Analog Input failures on 7KF02 modules

Dear Expert

recently, I got several Analog Input failures on 7KF02 modules and I found some question on 4 wire wiring of it.

All M- of 4 wire transmitters shall be tied into comp(10/11) of module and eventually it will tie with M of power for 2 wire. if 4 wire device make noise then all channels tie into Mana can be affected due to have same common point.

Could you let me know why M- of 4wire has to be connected Mana

appreciate you comment

Mike 

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Split from 6ES7331-7KF02-0AB0 AI Wiring.

JH5

Dear Expert

recently, I got several Analog Input failures on 7KF02 modules and I found some question on 4 wire wiring of it.

All M- of 4 wire transmitters shall be tied into comp(10/11) of module and eventually it will tie with M of power for 2 wire. if 4 wire device make noise then all channels tie into Mana can be affected due to have same common point.

Could you let me know why M- of 4wire has to be connected Mana

appreciate you comment

Mike 

------------------------------------------------------------------------------------------
Split from 6ES7331-7KF02-0AB0 AI Wiring.

 hi JH5

4 wire transmitter have separated power and analog signal cause for safety device for it, so u have 2 wire for power and 2 wire for analog signal, M- is 0V and Mana (M analog) need too connected to M- for loop connection

S7-300 module data, chapter4: principal of analog value processing

Electrically isolated transducers are not connected to local ground potential. They can be operated in electrically isolated mode.

Potential differences may develop between electrically isolated sensors. These potential differences may be caused by interference, or may develop as a result of the local

distribution of transducers.

In environments with a high level of EMC interference, it is advisable to interconnect M- with MANA in order to prevent the permissible CMV value from being exceeded.

Note: For modules where VCM ≤ 2.5 V, interconnect M- and MANA

 And also

Chapter6, module data sheet

Maximum potential difference:

• between inputs and MANA (VCM) : typ. 2.5 V DC (> 2.3 V DC)

• between inputs (VCM) : typ. 2.5 V DC (> 2.3 V DC)

 Hope this helps

 Regards

Hosein