In order to understand the meaning of the instruction, the first I_DI is to convert integer (16 bits) data into double integer (32 bits) data. As the name implies, the input is 16-bit integer and the output is 32-bit integer. The second DI_R is to convert double integer (32-bit) data into real number (32-bit). Because Siemens 200PLC does not directly convert integers (16 bits) into real numbers, it usually takes two instructions to convert integers into real numbers! When the analog module is involved in the conversion, because the analog-to-digital conversion is 16-bit integer data, and the engineering scalar of PID operation is in the range of-32,000 ~ 32,000 or 0 ~ 32,000, and the data during the operation are all real numbers less than 1, it is necessary to convert the analog-to-digital converted 16-bit data into real numbers, and then complete the operation.