The difference between thermocouples with exposed joint, grounded and insulated goes beyond the physical construction: each model has specific characteristics that influence the response speed, electrical protection and reliability of the temperature measurements. Understanding these variations is essential for selecting the appropriate thermocouple sensor and ensuring greater efficiency in industrial processes.
What is a thermocouple?
The thermocouple is one of the most widely used temperature sensors in industry. It works by connecting two different metals together at one end, called the junction. When this junction is exposed to a temperature change, a difference in electrical potential occurs between the metals, generating a signal that can be measured and converted to degrees Celsius or Fahrenheit.
Robust and capable of withstanding extremely high temperatures, the thermocouple adapts to a variety of scenarios, from laboratory experiments to heavy-duty operations in large industries. Furthermore, it offers a significant advantage: affordable cost combined with efficiency.
But not all models are created equal and there are some types of thermocouples. The way the joint is constructed directly influences performance. This is where the three most common types come in: exposed joint, grounded joint and insulated jointEach of them has advantages and limitations that need to be evaluated before choosing.
What is the difference between a thermocouple with an exposed joint, a grounded joint, and an insulated joint?
The exposed junction thermocouple has the junction in direct contact with the process. This ensures faster response times, making it ideal for gas measurements or situations where speed is a priority. The disadvantage is that there is no electrical isolation, leaving the sensor vulnerable to interference.
The grounded-junction thermocouple, on the other hand, has a welded joint on the metal sheath. It also offers fast response and good mechanical protection. However, because it is electrically connected to the process through the sheath, it can conduct interference and generate noise in the system.
The insulated junction thermocouple is the most widely used in industry. In this case, the junction is separated from the sheath by a layer of insulation, which ensures electrical safety and prevents interference. It's ideal for noisy industrial environments and automation systems. The response is slightly slower, but offers greater stability and reliability.
To exemplify the differences between exposed joint, grounded joint and insulated joint, we prepared a video explanatory that practically addresses how each type works and in which applications it should be used.
Thermocouple with exposed joint
In the exposed joint model, the joint is in direct contact with the process. This means there is no physical barrier between the joint and the environment being measured.
The main advantage of this type is its extremely fast response time. Because there's no mechanical protection, heat transfer occurs almost immediately, allowing accurate measurements in seconds. Therefore, it's widely used in gases, low-viscosity liquids, and applications where reading speed is a priority.
On the other hand, there are significant risks. Because the junction is not insulated, the sensor is electrically vulnerable and may suffer interference or even cause safety issues if used in inappropriate locations. Furthermore, its durability tends to be shorter in harsh environments, as the junction is exposed to wear.
Thermocouple with grounded joint
In a grounded joint, the joint is welded directly to the thermocouple's metal sheath. This ensures good physical protection while maintaining a fast response.
This model is recommended when seeking a balance between reading speed and mechanical strength. It works well on liquids, gases, and metal surfaces, making it a good choice for those who need robustness without sacrificing speed.
The point of concern is that, because it is electrically connected to the sheath, the thermocouple can conduct electrical interference from the process. This means that the system may exhibit noise in the reading signals, compromising accuracy in environments with high electrical noise.
Thermocouple with insulated joint
The insulated joint model is the most widely used in industry, especially in environments that require reliable and stable measurements. In this type, the joint is physically separated from the sheath by an insulating layer, preventing direct electrical contact.
The main advantage is electrical safety. This insulation protects against noise and ensures cleaner, interference-free signals, even in industrial environments with a high level of electronic equipment. Therefore, it is preferred in automation systems, PLCs, and control panels.
The downside is that, due to isolation, response time is slightly slower compared to other models. Even so, this difference is usually small compared to the gains in stability and reliability.
Which to choose?
The choice of thermocouple depends directly on the process in which it will be used.
- If the priority is speed, as in gases or fast processes, the model of exposed joint is the most suitable.
- If it is necessary resistance mechanics without losing much response time, the grounded joint may be the right choice.
- To noisy environments, automation systems and situations where electrical reliability is essential, the best option is to insulated joint.
Alutal is a reference in temperature measurement
A Total é reference in the instrumentation market and control, recognized for the quality and reliability of its products. With years of experience, the brand has established itself as a specialist in temperature sensors, thermocouples, and high-performance industrial solutions.
Furthermore, contacting Alutal is quick and easy. The company offers several customer service channels to facilitate communication with its customers. You can visit the official website, fill out the contact form, or even speak directly to the technical team by phone and email. This makes it easy to clarify questions, request quotes, or obtain specialized support.
