In today’s modern industrial setup, machines need to work smoothly and efficiently. In these systems, one small pressure deviation can lead to serious damage and ultimate failure. Hence, to ensure reliable pressure monitoring, the industry now relies on the modern devices known as 4-20 mA pressure sensors. At first, this technology may sound a bit technical, especially if you are new to automation. That’s why I will discuss the applications and wiring guide of 4-20 mA pressure sensors in industrial automation in this article. You will know how these sensors work and where they actually perform. So let’s get started.
What Is a 4–20 mA Pressure Sensor?
A 4–20 mA pressure sensor is a device that continuously measures pressure in a system. After that, it converts those measurements into an electrical signal. This signal is sent as a current that ranges from 4 milliamps (mA) to 20 milliamps (mA). That’s where it gets its name from. The 4 mA represents the minimum pressure. However, 20 mA represents the maximum pressure.
In simple terms, a 4-20 mA pressure sensor measures pressure using its internal sensing elements. When it feels any pressure change, it sends the information in electrical form. But have you ever wondered why 4–20 mA and not 0–20 mA? The concept is quite simple. First, the signal starts at 4 mA rather than 0 mA, making it easier for the system to detect faults.
If the signal drops to 0 mA, it clearly means something is wrong. For example, there might be a broken wire, a power failure, or sensor damage. So if the system uses 0–20 mA, then 0 mA could mean either “zero pressure” or “a fault.” Now the system would get confused. So, starting at 4 mA removes this problem.
Secondly, using 4–20 mA improves accuracy and stability. How? Actually, very low signals (close to 0 mA) are more affected by electrical noise and interference. Starting at 4 mA keeps the signal strong and clean. This gives more reliable readings even over long distances.
How Does a 4–20 mA Pressure Sensor Work?
The working principle of a 4-20 mA pressure sensor is very straightforward. First, it has a small internal pressure sensor. When the pressure is applied or changes from the normal value, this part slightly moves or changes. The sensor understands how much pressure is present based on this change. But this pressure information cannot be sent as it is. Therefore, the sensor changes that pressure into an electrical signal.
If the pressure is low, it sends a signal or an electrical current of around 4 mA. If the pressure increases, the current also increases, up to 20 mA. So, pressure and current move together—more pressure means more current. Now, finally, this current goes into the controller. The controller reads the current and understands changes in the pressure value. Then it can take actions such as controlling machines, issuing warnings, or keeping the system running safely.
Wiring Guide of 4-20mA Pressure Sensors for Industrial Automation: Step-by-Step
Have you grasped the basic know-how of the 4-20mA pressure sensor? Now the next common question is how to wire it. Remember, the pressure sensor’s accuracy depends entirely on proper wiring. So let’s dive in and discuss how wiring is done for 4-20mA pressure sensors.
Step 1: Identify Terminals
The first and most important step in wiring a 4–20mA pressure sensor is to identify its terminals. Remember, every pressure sensor has connection points. At these points, the wires are attached. However, not all those connection points are the same across sensors. Instead, they vary from model to model. Usually, you will see labels like + (positive), – (negative).
Sometimes there is also a signal or ground wire on a 4–20 mA Ceramic Pressure Sensor PS100E03.
These markings tell you where each wire should go. To confirm these markings, always check the sensor’s datasheet or manual. However, never rely only on guesswork, because different sensors may use different labeling styles. Generally, connect the power supply to the positive terminal (+). Meanwhile, the negative (–) completes the loop back to the system. If there is also a signal terminal, it will send the current reading to the controller.
Step 2: Connect Power Supply
After you identify the terminals, connect the power supply to the sensor. Mostly, the ceramic 4–20 mA pressure sensors use a 24V DC power supply. Now you have to connect this DC supply to the sensor’s terminals. For example, connect the power supply’s positive (+) terminal to the sensor’s positive (+) terminal.
Then connect the negative terminal to the sensor. However, this negative terminal should not stop here at the sensor. Instead, it must pass through the rest of the circuit (like the PLC) and return to complete the path. This is called a complete loop, and it allows the current to flow along a complete path, helping the system work. Remember, if you make a slight mistake in the power supply connection, the sensor will not work at all.
Step 3: Connect to PLC or Controller
Once you are sure the DC power is connected to the sensor, connect the sensor to the PLC. But what is a PLC? Actually, a Programmable Logic Controller (PLC) is a device that reads signals from sensors. It then uses that information to control machines. In simple words, it is the “brain” of the system. As you know, the sensor produces a small current (4–20 mA).
However, this current is not random—it carries the pressure information. So you have to connect the sensor output wire to the PLC’s analog input terminal. This is the point where the PLC “reads” the signal. When the connection is done correctly, the PLC starts receiving the current signal. After that, it converts those signals into a readable pressure value.
Step 4: Complete the Loop
Now the 4-20mA pressure sensor is connected to the PLC, right? The final step is completing the electrical loop. Remember, if the circuit is not complete, the sensor will not work properly, and the PLC will not receive any signals. So to complete the loop, you have to connect the remaining wire from the PLC or sensor back to the negative terminal of the power supply.
This closes the entire electrical circuit. Now, the electricity flows continuously from the power source through the sensor into the PLC and then returns. As a result, the sensor starts working and detecting any pressure changes in the system.
Common Applications of 4–20 mA Pressure Sensors
The 4-20 mA pressure sensors are known for their accuracy and precision. That’s why they have become the most important part of almost every industry. So let’s discuss the industry that relies most on these pressure sensors.
1- Oil & Gas Industry
The most important user of the 4-20mA pressure sensor is the oil and gas industry. As you know, this sector is very critical, and pressure is related to safety and production. If there is a sudden drop or rise in pressure, the results will be dangerous. For example, high pressure can cause pipelines to burst. Therefore, the pressure sensors are installed in pipelines, drilling machines, and storage tanks. There, these sensors continuously monitor pressure changes. If there is any change, the control system takes action immediately.
2- Water Treatment Plants
Water treatment plants often use filters, pumps, and pipes through which water flows. At all these stages, the right pressure is crucial for cleaning the water. If pressure drops or rises too much, it can affect water quality. That’s where the 4-20 mA pressure sensor performs. It monitors the system in real time through filters, pumps, and pipes. For example, it can detect when a filter is blocked or when a pump is not working properly. In this way, the pressure sensor helps smooth the operation of the water treatment plants.
3- Chemical Processing
Another sector where you will find the 4-20mA pressure sensor is chemical processing systems. These chemical plants handle various liquids and gases. However, liquids and gases often need careful pressure control. Even a small pressure error can lead to unsafe reactions or product damage. A 4-20mA pressure sensor here monitors pressure inside reactors, pipes, and tanks. If something goes wrong, the system can quickly respond. For example, it might stop or adjust the process to prevent leaks.
4- Manufacturing Industry
In manufacturing, many machines rely on air or hydraulic pressure to operate properly. If this pressure exceeds the safe limit or drops too low, the machine will stop working. That’s why pressure sensors are used in these machines to make sure everything runs smoothly. How? The pressure sensor helps control presses, robotic arms, and pneumatic systems. Factories can now detect problems early, such as low pressure or system leaks.
5- HVAC Systems
HVAC systems maintain proper airflow and pressure to keep the indoor environment comfortable. These systems usually use ducts, filters, and fans. However, in all three parts, the right pressure is crucial. That’s why the 4-20 mA pressure sensors are used to maintain and detect that pressure. For example, if a filter is blocked, the pressure changes there quickly. Now the sensor immediately detects it and sends signals to control and maintain good air quality.
6- Food & Beverage Industry
Lastly, the food and beverage industry relies on 4-20 mA pressure sensors. Actually, in food factories, machines fill bottles and packets with products like juice, milk, oil, and sauces. If the pressure is too high or too low, bottles can be overfilled or underfilled.
To resolve this issue, a 4–20 mA pressure signal continuously monitors the pressure inside these machines. It tells the system whether everything is normal. Also, these sensors work effectively even with steam, hot water, and cold water that are common in the food industry. The standard pressure sensors often fail in such wet or harsh environments.
Important Wiring Tips for 4-20mA Pressure Sensors
Wiring plays a crucial role in the efficient working of the pressure sensors. Even a small mistake can affect the whole system. To avoid those mistakes you can easily make, here are some factors you must consider before wiring.
- Use proper cables: First, ensure you use the right ones. Always use a high-quality cable, preferably a shielded one. Shielded cables protect the signal from electrical noise caused by machines, motors, or power lines.
- Avoid Loose Connections: Secondly, make sure all wire connections are tight and secure. Remember, loose connections can break the flow of current, even for a short time. This then causes the PLC to show wrong or fluctuating readings. So make sure there are no loose connections at all.
- Check Polarity: Polarity means connecting positive (+) and negative (–) wires correctly. If you mix them up, the sensor will not work properly. In some cases, it may not turn on at all. Therefore, I recommend you always double-check the wiring diagram before powering the system.
- Test Before Final Use: Lastly, before using the sensor in real operation, always test the wiring setup. For instance, turn on the power and check if the PLC is reading the correct pressure signal. If there is any problem, you can fix it at this stage before full operation starts.
결론
Pressure monitoring is the most crucial part of any industrial system. A sudden drop or rise in the system can cause serious problems, such as damage to machinery or system failure. To ensure the correct pressure in any industrial system, 4-20 mA pressure transducers come into play. These are specialized, accurate devices that precisely monitor pressure changes. In any change in pressure, the sensing part immediately moves.
This sends electrical signals to the controller. The controller then takes action to stabilize the pressure or adjust machine parts. But in all this, proper wiring matters a lot. In this wiring guide, I have discussed some steps to help you fully understand it. Due to this accuracy, the 4-20 mA pressure sensors have become a favored choice in several industries. For example, you can find them in chemical and water treatment plants. Also, they are used in HVAC systems, food, and beverages.