Siemens S7 - 200 PLC power demand and computation

S7- 200 CPU module provides 5 VDC or 24 VDC power supply: the CPU when a extension module through the I/O bus with 5 v power supply, all the extension module 5 v power consume no more than the sum of the CPU provides power rating. If not enough use cannot be an external 5 v power supply. Each CPU has a 24 VDC power supply sensor, it is the machine input point and extension module input point and extension modules provide 24 VDC relay coil. If the power supply requirements is beyond the power rating of CPU module, you can increase the 24 VDC power supply to provide an external extension module. The so-called power calculation, is to use the CPU can provide power supply capacity, minus the needed for each module's power consumption. Note: EM277 module itself does not need to be 24 VDC power supply, the power supply is used for communication port. 24 VDC power supply demand depends on the size of a load on the communication port. CPU communication port, can connect to the PC/PPI cable and TD 200 and power supply for them, the power consumption is not included in calculation.