When it comes to industrial field signals, friends who have been in the industrial circle for a long time may be familiar with them, they are "analog" and "switching" signals. The emergence of these two signals solves most of the industrial signal transmission problems in industrial automation. Today, let's take a look at the characteristics of these signals and what scenarios they are used in.

analog signal

First of all, let's take a look at what is called an analog quantity, which starts with an analog signal. An analog signal is a continuously changing physical quantity, usually in the form of voltage or current. The signals collected by most sensors are analog signals, which generally change continuously, such as temperature and humidity sensors, light sensors, etc. These signals are continuous and can be called analog signals.

switch signal

Another type of signal is the switch signal, which differs from the analog signal in that the switch signal is a discontinuous signal. The switch signal has only two states of "on" and "off", or it can be called "on" and "off". This type of signal is divided into two types: active and passive. The active signal is called "wet contact" signal, and the passive signal is called "dry contact". General travel switches, float switches, etc. are all switch sensors, generally wet node sensors need to pay attention to polarity issues, dry nodes do not.

The International Electrotechnical Commission (IEC) has determined the current signal 4mA~20mA (DC) and the voltage signal 1V~5V (DC) as the unified standard for analog signals in process control systems. Therefore, a sensor that meets this standard is also called a transmitter.

The output of the sensor is generally a current or voltage signal, but this type of signal will be disturbed during the transmission process, which is not conducive to long-distance transmission and processing of the control equipment, so the remote IO module will be used here.

The use of remote IO can not only reduce signal reduction, but also save equipment investment and cable costs.

The sensor collects the signal and converts various quantities (temperature, humidity, etc.) ModBus protocol, thus forming a unified communication protocol.

Usually, the serial port remote acquisition module generally converts 4mA~20mA(DC) to ModBus RTU protocol, and the Ethernet remote acquisition module generally converts 4mA~20mA(DC) to ModBus TCP protocol.

In the industrial control system, the remote I/O module device collects the data collected by the sensor and converts it into the ModBus protocol, so that the data can be transmitted over a long distance through the serial port or Ethernet interface. Ethernet devices can be directly connected to switches or routers to directly form a local area network, so that data can be uploaded to the cloud and remote supervision can be realized, which is the origin of the Industrial Internet of Things. The automatic control of the equipment can be realized through PLC or HMI, industrial computer and other equipment.