Tag: plc

Speed control is generally achieved by inverters, servo motors to do speed control, is generally used for rapid acceleration and deceleration or speed precision control occasions, because relative to the inverter, servo motors can reach thousands of revolutions within a few millimeters, because the servo is closed-loop, the speed is very stable. Torque control is mainly to control the output torque of the servo motor, again because of the fast response of the servo motor. Application of the above two kinds of control, you can treat the servo drive as a frequency converter, generally with analog control.

Programmable Logic Controller referred to as PC or PLC is an electronic system operated by digital operations, specially designed for application in an industrial environment. It uses a memory that can be programmed to execute instructions for storing logical operations and sequence control, timing, counting and arithmetic operations, and through digital or analog input (I) and output (O) interfaces, controls various Type of mechanical equipment or production process. PLC is developed on the basis of electrical control technology and computer technology, and gradually developed into a new type of industrial control device with microprocessor as the core and integrating automation technology, computer technology and communication technology. PLC has been widely used in the automatic control of various production machinery and production processes. 

Programmable Logic Controller, short for PLC, is a digital electronic device with a microprocessor. The device is a digital logic controller for automatic control, which can load control instructions into the memory at any time for storage and execution. The programmable controller is composed of internal CPU, instruction and data memory, input and output units, power supply modules, digital and analog units.

When the PLC is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution and output refresh three stages. Completing the above three stages can be called a scan cycle. During the entire operation, the CPU of PLC repeatedly executes the above three stages at a certain scanning speed.

In PLC control system, we mostly use DC proximity sensors. And in DC circuit, the proximity sensors used include 2-wire proximity sensor, 3-wire proximity sensor and 4-wire proximity sensor. And they can be further divided into NPN type and PNP type. Generally, people in the United States and Japan usually use NPN proximity sensor, while in the Europe use the PNP proximity sensor.
The difference of NPN proximity sensor and PNP proximity sensor lies in the conduction situation. NPN proximity sensor belongs to the low level conduction and PNP proximity sensor belongs to the high level conduction. In other words, signal of the NPN proximity sensor flows from the load to the proximity sensor, while that of the PNP proximity sensor flows from the proximity sensor to the load.
We will take FX3U PLC and S7-200 PLC as examples to explain how is the NPN proximity sensor and PNP proximity sensor connected to PLC.

In our load cell product pages, when we introducing the load cells, we often say that you can buy a transmitter/amplifier with a customized output signal (0-5V, 0-10V, 4-20mA) to output standard signal to PLC, DCS and other control systems. Then someone will ask us how to connect load cell to plc. Now today we will explain the connection methods of load cell in details. When forming the weighing and batching control system with PLC, there are four connection methods for load cell.