SIMATIC S7-1500 PLC Application Examples

[Example] There is a control system, the controller is CPU 1511C-IPN, the pressure sensor measures the oil pressure, the oil pressure range is 0 ~ 10MPa, when the oil pressure is higher than 8MPa, an alarm will be triggered. Please design this system.

[Answer] CPU 1511C-1PN integrates analog input/output and digital input/output. Its wiring is shown in Figure 1. Terminals 1 and 2 of the analog input are respectively connected to the current signal + and current signal - of the sensor.

Figure 1

Numeric Conversion (FC105) The SCALE function accepts an integer value (IN) and converts it to a real value between the lower and upper limits (LO_LIM and HI_LIM) of the engineering units table.

① Create a new project. Create a new project "Alarm". In the project tree of the TIA Portal software project view, click "Add New Block" to create a new program block. The block name is "Pressure Acquisition". Select the programming language as "LAD" and the block type as "Function FC". Then click the "OK" button, as shown in Figure 2, to generate function FC1, whose programming language is LAD.

Figure 2

② Define the variables of the function. Open the newly created function "FC1" and define the input variable (Input), output variable (Output) and temporary variable (Temp) of function FC1, as shown in Figure 3. Note: These variables are local variables and are only valid within this function.

Figure 3

③Insert the SCALE instruction. Click "Instructions" → "Basic Instructions" → "Original" → "SCALE" to insert the SCALE instruction.

④ Write the LAD program of function FC1 as shown in Figure 4.

Figure 4

⑤ Add loop organization block OB30 and write LAD program, as shown in Figure 5. The pin of FC1 is very similar to CALE in the instruction, and the pressure variable range collected is within 0~10MPa.

Figure 5