These transmitters include pressure transmitters, level transmitters, temperature transmitters, differential pressure transmitters, humidity transmitters, and soil moisture transmitters, among others. The usage of these transmitters is becoming increasingly widespread in industrial applications.
Types of Transmitter Power and Signal Outputs
Transmitters typically use two main power supply configurations:
- Two-wire system: Where both power and signal transmission occur over two wires.
- Four-wire system: Where separate wires are used for power and signal transmission.
Transmitters can output signals in different formats, depending on the type of transmitter. Common signal outputs include:
- Analog signals:
- 4-20mA current signals
- 0-5V or 1-5V voltage signals
- Digital signals: RS485 is a commonly used digital communication protocol.
Connecting Transmitters to PLC/DCS/FCS/MCU/FA/PC Systems
To successfully connect various transmitter signals to PLCs, Distributed Control Systems (DCS), Fieldbus Control Systems (FCS), Microcontroller Units (MCU), Factory Automation (FA) systems, or PCs, it is necessary to match the technical characteristics and functions of the transmitters with those of the data acquisition system. This involves:
- Matching the power supply: Different power requirements of transmitters and PLCs must be considered.
- Handling EMC interference: The electromagnetic compatibility (EMC) issues need to be managed to ensure reliable signal transmission.
Typically, the signals from the transmitters are isolated, amplified, and converted before being sent to the PLC. The PLC then collects either analog or digital signals from the transmitter and processes them.
- If the transmitter outputs analog signals, the PLC requires an analog input interface.
- If the transmitter outputs digital signals, the PLC requires a digital input interface.
Analog Control Systems
In closed-loop control systems that deal with analog signals, the system must include both digital (on/off) inputs and outputs and analog inputs and outputs. This configuration allows for the continuous adjustment and control of parameters like:
- Temperature
- Flow rate
- Pressure
- Displacement
- Speed
The continuous regulation of these parameters relies on the ability to sample analog inputs and adjust outputs accordingly.
Digital Control Systems
For digital control systems, particularly when using devices like rotary encoders and pulse servo devices (such as stepper motors), PLCs can receive and output high-speed pulses. This capability enables digital control, where the system can handle tasks requiring precise movement and control.
More advanced PLCs include specialized digital control modules that enable functions like curve interpolation, allowing the system to perform smooth, precise movements based on digital commands. Recently, new motion unit modules have been introduced, enhancing the PLC’s ability to handle digital control. These modules often come with programming languages tailored for digital control, making it easier to implement digital control solutions.
Summary
In summary, connecting transmitters to PLCs or other data acquisition systems requires careful consideration of power supply types, signal formats, and environmental interference. The PLC can handle both analog and digital signals, depending on the input/output interface required. Advanced PLCs also feature capabilities for high-speed digital pulse control and specialized motion modules, making them versatile for various industrial automation tasks.