1747-L541 Analogue Data Transmission

1747-L541 upper computer will receive the data completely, after data processing shows the waveform curve of the unit operation quantity U, If, P, Q, Ug (voltage given) in 7 seconds before the fault and 13 seconds after the fault, so that the generator fault can be analysed. In this system, PLC selected SIMATIC S7-226; analogue module selection and S7-226 supporting products EM235; PLC and computer through the PC / PPI cable connection to communicate in serial mode.

The 1747-L541 programme sends the sampled data to the respective data blocks every 40 ms. A data pointer is defined for each data block with its initial value pointing to the first address of the respective data block. Each time data is transmitted, the respective pointer is moved down by 2 bytes. The first 7 seconds of data (350 bytes) are recorded cyclically, i.e., if the data is full before the fault arrives, the data pointers will point to the first address of the data block again. The definition pointer index is used to record the position at which the 20 seconds of fault data begins. When the fault arrives, the data pointer points to the 13 seconds of data after the fault (the last 650 bytes), at this time the pointer index will be divided into the first 7 seconds of data before and after the two parts, the correct order is to swap the two parts before and after. When the latter 13 seconds of data are recorded, the recording subroutine ends.

In the communication subroutine, the 1747-L541 first stops the reception of the free port, then transfers the data with the pointer tran_pointer as the first address and the size of 200 bytes to the send buffer, and then sends it out through the serial port with the send command. Every time the data is sent, the pointer tran_pointer is moved down 200 bytes, the value of variable count is increased by 1, and M6.0 is reset. When the host computer sends the 26th transmission command, the 5000 bytes of the data area VW4000 ~ VW8998 in PLC have been sent out, and then the rated voltage, rated current, rated active power, rated reactive power and the pointer index are sent out, the count value is cleared to zero, and the pointer tran_pointer is re-initialised, and the M6.0 is reset.