What are the two working states of PLC? What signals does PLC process?

What are the two working states of PLC?

PLC has two working states: running state and stopping state.

Running state: When the PLC is in the running state, the input module collects external signals, the CPU performs logical operations according to the pre-written program, and the output module controls external devices. The PLC can realize various logical control functions in the running state and realize industrial automation control.

Stop state: When the PLC is in the stop state, the input module no longer collects external signals, the CPU stops performing logical operations on the program, and the output module no longer controls external devices. The PLC cannot control external devices in the stop state. At this time, the PLC can be operated by parameter setting, program modification, fault diagnosis, etc. The working state of the PLC can be switched through the PLC operation panel, programming software, etc. It should be noted that when the PLC is in the running state, the PLC should be avoided from parameter setting, program modification, etc., so as not to affect the normal operation of the PLC.

PLC has the following requirements for input signals:

The electrical characteristics must meet the requirements of the PLC input module: The electrical characteristics of the input signal should meet the requirements of the PLC input module. For example, the input voltage, current, frequency, etc. should be within the range specified by the PLC input module.

Signal stability should be good: The input signal should be stable and reliable to avoid signal jitter or interference that may cause PLC misjudgment or malfunction.

The signal sampling period must meet the requirements: The PLC input module has certain requirements for the input signal sampling period. The input signal should be sampled and processed according to the sampling period to ensure sampling accuracy and signal stability.

The input signal should meet the logic requirements: The input signal should meet the logic program requirements written by the PLC. For example, for digital input signals, a switch input module should be used; for analog input signals, an analog input module should be used.

The input signal should match the external device: The input signal should match the external device, for example, the interface of the sensor and PLC input module should match, and the voltage and current of the input signal should match the external device.

These are the basic requirements of PLC for input signals. The quality and stability of input signals have an important impact on the control accuracy and reliability of PLC.

What signal does PLC process?

The signals processed by PLC can be divided into two types: digital and analog:

Digital signal: A digital signal refers to a signal with only two states, such as a switch signal, a button signal, a sensor signal, etc. PLC collects digital signals through digital input modules, and after logical processing, controls external devices through digital output modules. Digital signal processing is simple and is suitable for binary control of external devices.

Analog signal: Analog signal refers to a signal whose size can change continuously, such as temperature signal, pressure signal, flow signal, etc. PLC collects analog signals through analog input modules, and controls external devices through analog output modules after A/D conversion and logic processing. Analog signal processing is complex and is suitable for occasions where external devices are precisely controlled and adjusted. In actual industrial control, PLC usually needs to process various types of digital and analog signals, and control and adjust external devices through logic processing and control output signals. In addition, PLC can also process special types of signals such as communication signals, pulse signals, encoder signals, etc.