Comparing Open Loop and Closed Loop Current Sensors: Pros and Cons

Current sensors are essential components in various industrial applications, allowing for accurate measurement and monitoring of electric current. One important distinction in current sensor technology is the classification into open loop and closed loop current sensors. In this blog post, we will compare these two types of current sensors, discussing their advantages and disadvantages, to help understand their suitability for different industrial automation scenarios.

I. Open Loop Current Sensors:
Open loop current sensors, also known as non-contact current sensors, measure the magnetic field generated by the current-carrying conductor without any physical contact. They offer several advantages and disadvantages.

Advantages:
1. High Isolation: Open loop current sensors provide galvanic isolation, ensuring that the measurement circuitry is electrically separated from the high-current path. This isolation protects sensitive electronics, enhances safety, and minimizes the risk of electrical faults.

2. Wide Measurement Range: Open loop current sensors can handle a wide range of current values, making them suitable for various applications, from low current measurements to high current industrial processes.

3. Easy Installation: These sensors do not require breaking the electrical circuit, simplifying installation and reducing downtime during sensor integration into existing systems.

Disadvantages:
1. Limited Accuracy: Open loop current sensors are susceptible to external factors such as temperature variations, electromagnetic interference, and magnetic field distortions. These influences can introduce measurement errors and reduce accuracy compared to closed loop sensors.

2. Lack of Linearity: The output of open loop current sensors may not be linearly proportional to the measured current, requiring additional calibration or compensation techniques for accurate readings.

II. Closed Loop Current Sensors:
Closed loop current sensors, also referred to as conventional current transformers (CTs), rely on a magnetic core and secondary winding to measure current. They also have distinct advantages and disadvantages.

Advantages:
1. High Accuracy: Closed loop current sensors offer superior accuracy compared to open loop sensors. They provide precise measurements even in the presence of external disturbances, ensuring reliable and consistent results.

2. Excellent Linearity: These sensors exhibit a linear relationship between the primary current and the secondary output, simplifying calibration and eliminating the need for additional compensation techniques.

3. Robustness: Closed loop current sensors are less susceptible to environmental influences, such as temperature variations and electromagnetic interference, ensuring stable and accurate measurements in challenging industrial environments.

Disadvantages:
1. Limited Dynamic Range: Closed loop current sensors have a narrower dynamic range compared to open loop sensors. They may not be suitable for applications involving extremely high or low currents.

2. Bulk and Size: Due to the presence of a magnetic core and the requirement of a secondary winding, closed loop current sensors tend to be larger and bulkier than open loop sensors. This factor may pose challenges in space-constrained industrial environments.

Conclusion:
The choice between open loop and closed loop current sensors depends on the specific requirements of the industrial automation application. Open loop sensors offer advantages such as high isolation, wide measurement range, and ease of installation. However, they may suffer from limited accuracy and lack of linearity. On the other hand, closed loop sensors provide high accuracy, excellent linearity, and robustness, but have a limited dynamic range and are bulkier in size. Understanding these pros and cons will help engineers and system integrators make informed decisions when selecting the most appropriate current sensor technology for their specific industrial automation needs.