Hall effect sensors are widely used for precise, contactless current measurement in applications ranging from industrial automation to renewable energy systems. LEM, a leading manufacturer of current and voltage sensors, offers both open-loop and closed-loop Hall effect sensors, each with distinct advantages. Open-loop Hall effect sensors offer simpler, cost-effective solutions with wider ranges but lower accuracy, while closed-loop sensors provide higher accuracy and faster response through compensation, at the cost of complexity and size.
In this blog, we’ll explore how Hall effect sensors work, compare open-loop and closed-loop types, and highlight specific LEM models along with their applications.
How Hall Effect Sensors Work
As we highlighted in the previous blog related to Hall Effect Sensors: An Introduction, they operate on the Hall effect principle – discovered by Edwin Hall in 1879. When an electric current flows through a conductor or semiconductor placed in a perpendicular magnetic field, it experiences a force that pushes charge carriers (electrons or holes) to one side. This results in a voltage difference across the conductor, known as the Hall voltage.
Types of Hall Effect Sensors
Hall effect sensors are available in two primary types:
1. Open-Loop Hall Effect Sensors
These measure the magnetic field directly and output a proportional voltage. These are simpler, cost-effective, and energy-efficient but less accurate.
2. Closed-Loop Hall Effect Sensors
These use a compensation coil to counteract the magnetic field and maintain accuracy. They are more precise, stable, and fast-responding but require more power.
Now, let’s dive deeper into each type.
Open-Loop Hall Effect Sensors
Design: These sensors have a Hall effect sensor placed in the air gap of a magnetic core. The current-carrying conductor passes through this core, generating a magnetic field that is measured by the Hall sensor.
Measurement: The Hall sensor’s output voltage is directly proportional to the magnetic field, which in turn is related to the current. This output is then amplified to provide a usable signal.
Advantages
✔ Lower cost
✔ Compact and lightweight
✔ Low power consumption
✔ Suitable for DC, AC, and pulsed current measurements
Limitations
✖ Lower accuracy compared to closed-loop models
✖ Limited frequency bandwidth
✖ More affected by temperature variations and external magnetic fields
Common LEM Open-Loop Models are HAS series, HAT Series, HAX series
Closed-Loop Hall Effect Sensors
How They Work
Design: These sensors also use a Hall effect sensor and a magnetic core, but they include a compensation circuit – ie, a feedback coil to generate a counteracting magnetic field.. This stabilizes the Hall voltage, improving accuracy and response time while minimizing external influences.
Measurement: The Hall sensor in a closed-loop sensor operates in a “zero-flux” condition. The compensation current is adjusted to maintain this condition, and the value of this current is proportional to the primary current.
Advantages
✔ High accuracy and linearity
✔ Fast response time
✔ Less affected by external magnetic fields and temperature variations
✔ Ideal for precision applications
Limitations
✖ Higher cost
✖ Requires more power compared to open-loop sensors
Common LEM Closed-Loop Models are LA 25-NP, LA 100-P, LA 305-S etc
In summary:
| Feature | Open-Loop Hall Effect Sensor | Closed-Loop Hall Effect Sensor |
| Design | Simpler | More complex |
| Accuracy | Lower | Higher |
| Linearity | Lower | Higher |
| Temperature Drift | More susceptible | Less susceptible |
| Response Time | Slower | Faster |
| Cost | Lower | Higher |
| Size | Smaller | Larger |
| Power Consumption | Lower | Higher |
| Dynamic Range | Wider | Narrower |
Choosing the Right Sensor for Your Application
If cost and power efficiency are your main priorities, open-loop sensors (e.g., HX 03-P, HAS 50-S) are ideal.
Applications of LEM Hall Effect Sensors
LEM’s Hall effect sensors are widely used in:
- Industrial automation – Motor control, power monitoring, and factory automation.
- Renewable energy – Solar inverters, battery management systems, and wind turbines.
- Automotive applications – Electric vehicle battery management, regenerative braking, and ABS systems.
- Consumer electronics – Power supplies and home automation.
Conclusion
Hall effect sensors provide a non-contact, efficient, and accurate way to measure current. LEM’s open-loop sensors offer affordability and simplicity, while closed-loop sensors provide high precision and stability for demanding applications.
For detailed specifications, explore LEM’s official product catalog or contact Globetek – we are LEM’s oldest distributors in India – and would be happy to assist you in end-to-end procurement of hall effect sensors.
