Understanding the Role of Transmitters in Process Control Systems

Transmitters are the backbone of modern process control systems. They convert raw sensor data into signals that controllers can understand. This guide explains what transmitters do, their types, and why they’re critical for safe, efficient industrial operations.

Transmitters are essentially instruments that serve as the communication link between physical processes and automated control systems. They convert sensor-based inputs into data.

The control systems use this data to regulate or monitor a particular process.
ABB temperature transmitters regulate and maintain the temperature inside industrial facilities and vital machinery. Let us explore more about these instruments in detail below.

What Does a Transmitter Do in a Control Loop?

Transmitters are essentially sensors that convert the raw electrical signals from various sensors into standard electrical signals for Programmable Logic Controllers. The standard values for these electrical signals vary between 4 to 20 milliamperes.

The sensors from which they convert data are of the following types, namely:

• Pressure: which maps the pressure of fluids/gases inside compressed machinery or environments
• Flow: which maps the flow of liquids/gases through critical pipelines
• Temperature: which maps the temperature inside a particular equipment or industrial environment

Based on the input from these transmitters, the controllers then decide which action to take and generate an output signal accordingly. This signal is then transmitted to the actuator, which actually controls the function.

Take a look at our diagrammatic representation of how a transmitter works below:

Diagram: How a Transmitter Works

Let’s now take a look at the various types of transmitters below.

What Are the Main Types of Transmitters?

Take a look at the table below to understand more about the different types of transmitters in the table below:

Transmitter Type	Sensors Receive Raw Signals From	What Kind of Data Does It Transmit?	Common Applications
Pressure Transmitter	Piezoelectric, Capacitive, Vacuum, Strain Gauge	Pressure (gauge, absolute, differential)	Oil & gas, water treatment, chemical plants
Temperature Transmitter	Thermocouples, Resistance Temperature Detectors	Temperature	Boilers, HVAC systems, industrial furnaces
Flow Transmitter	Magnetic, Optical, Turbine Flow	Flow rate of liquids/gases	Pipelines, food processing, and pharmaceuticals
Level Transmitter	Hydrostatic, Ultrasonic level, Liquid level	Fluid or solid level	Tanks, silos, wastewater plants
pH Transmitter	Consumer-grade, Micro pH, Industrial pH	Acidity/alkalinity (pH level)	Water quality, chemical manufacturing
Humidity Transmitter	Thermal, Resistive, Capacitive	Relative humidity (%)	Clean rooms, HVAC systems, electronics production
Conductivity Transmitter	Inductive, 2-pole, and 4-pole	Electrical conductivity	Water treatment, chemical analysis

Table 1: Main Types of Transmitters

How Do Transmitters Differ from Sensors?

One of the most basic differences between transmitters and sensors is that sensors are devices that detect and measure changes or differences in physical parameters like temperature, humidity, and pressure. They convert this data into raw signals. Transmitters convert these raw signals into standardized electrical signals that control systems like ABB PLC Control Panels can add.

Let’s explore some other crucial differences in the table below:

	Transmitters	Sensors
Processing Capabilities	They process, correct, and calibrate raw sensor signals to provide the desired output.   Their output is in the form of standardized signals.	They do not process, correct, or calibrate the data they map.   They just transmit signals as they receive them to the transmitters.
Communication Capabilities	These devices remain in constant communication with control systems like ABB PLC Control Panels, for example.	Do not communicate with any systems
Integration Capabilities	Can be integrated into various devices	Function independently
Types	Conductivity, Pressure, Humidity, Flow, pH	Inductive, Temperature, Pressure, pH

Table 2: Differences between sensors and transmitters

How Do Analog Transmitters Differ From Digital Transmitters?

Let us take a look at the differences between digital and analog transmitters in the table below:

Feature/Characteristic	Analog Transmitters	Digital Transmitters
Signal Format	4–20 mA	Digital protocols (HART, PROFIBUS)
Data Type	Single variables	Multiple parameters
Accuracy & Noise	Moderate, noise-sensitive	High accuracy, resistant to noise interference
Use Case	For feedback in live applications	To facilitate communication with control systems

Table 3: Analog Transmitters vs Digital Transmitters

What Output Signals Do Transmitters Use?

Transmitters use a variety of output signals, namely:

● Electrical Signals: 4-20 milliamperes

Industries like oil and gas and manufacturing commonly use these signals for various applications. They transmit easily over long distances, making them ideal for wide-scale industrial usage.

● Digital Signals: HART or Highway Addressable Remote Transducers

Electrical signals and digital data combine and travel on the same wires as electric signals. These signals allow for remote communication for compensating and calibrating signals.

● PROFIBUS Signals

These signals are transmitted between sensors placed in the field and control systems like ABB PLC Control Panels. A PROFIBUS network is often used to transmit these signals, especially in large industrial setups.

● MODBUS Signals

They are used to ensure the automation of various industrial processes, like temperature regulation inside manufacturing facilities, for example.

The types of signals used depend on the length of the transmission channel, industry size, and compatibility with the controllers.

How Do Transmitters Improve Efficiency and Safety?

Transmitters often receive real-time data from various systems, which ensures that no information is lost in the feedback loop. This information allows for processes like the automatic opening or closing of valves or hatches.

For example, ABB temperature transmitters receive data from temperature sensors used in oil and gas drilling, storage tanks, and pipelines. They transmit this data to control systems above the ground.

The professionals can then take appropriate measures like halting the drilling, reducing the quantity of drilled petroleum being transported through pipelines, and so on. This ensures that the people stay safe, since excessively hot petroleum, in the presence of oxygen, can combust.

How Should You Choose Your Transmitters?

You should choose your transmitters by considering factors like the sensors and control systems involved, and their functional environment. For instance, if you work in the oil and petroleum drilling industry, you should use pressure, temperature, and flow transmitters.

This will help you use them correctly. Apart from that, you should also keep calibrating and testing these transmitters to ensure that they are functioning correctly.

Bridge the Physical and the Digital

Transmitters play a critical role in turning the raw input from sensors into actionable data. They help regulate various physical processes by transmitting this actionable data to the concerned control systems.

These control systems then pass on the signal to actuators, which control various processes.

By choosing the right type and understanding how they interact with control systems, you can improve performance, reduce downtime, and maintain precision in any process industry.