Water level control case with PLC, touch screen and inverter control

Today I will mainly share with you a real case involving a water level control project with PLC, inverter, and touch screen. Let’s take a look at the whole process. You can save it for future use!

● Project Description

● EM235 module

● Project realization

● Touch screen monitoring

01 Project Description

1. Project control requirements

The water tank supplies water to external users, and the water consumption is unstable, sometimes large and sometimes small. The water inlet of the water tank can be pumped into the water tank by a water pump. Now it is necessary to control the water level in the water tank and adjust it within the range of 0~200mm (the maximum value data can be determined according to the height of the water tank). If the water level value of the water tank is set to 100mm, then no matter how the water output of the water tank is, the water inlet is adjusted to require the water level of the water tank to be maintained at 100mm. If the water output is small, the water inlet should be controlled to be small, and if the water output is large, the water inlet should be controlled to be large.

2. Control ideas

Because the liquid level is proportional to the water pressure at the bottom of the tank, a pressure sensor can be used to detect the pressure at the bottom of the tank to determine the liquid level.

The PD algorithm is used to automatically adjust the water level. The water level signal 4~20mA detected by the pressure sensor is sent to the PLC, and the PLC performs PID calculation on the deviation between the set value and the detected value. The calculation result is output to adjust the speed of the water pump motor, thereby adjusting the water intake. The speed of the water pump motor can be adjusted by the frequency converter.

3. Component selection

1) PLC and module selection. The PLC can be S7-200cPU224. In order to receive the analog signal of the pressure sensor and adjust the speed of the water pump motor, an EM235 analog input and output module is selected.

2) Inverter selection: In order to adjust the water inlet, Siemens G110 inverter is selected.

3) Touch screen selection: Siemens human-machine interface TP170B touch screen is selected.

4) Water tank object equipment is shown in the figure below.

02 EM235 module

EM235 terminals and wiring

03 Project Implementation

1. PLC IO allocation and circuit diagram

PLC IO allocation

Start button, 10.0;

stop button, 10.1;

Q0.0, controls the operation of the water pump motor.

04 Touch screen monitoring