Hall Effect Current Sensors
Three of the LEM technologies (open loop, closed loop and Eta) are based on the Hall effect, discovered in 1879 by American physicist Edwin Herbert Hall at Johns Hopkins University in Baltimore. They are used in both our current sensors and voltage sensors portfolios.
Hall Effect - Current Sensors Technologies
Open Loop Current Sensors (O/L)
Open loop current sensors use the simplest implementation of the Hall effect. They provide the smallest, lightest, and most cost effective current measurement solution while also having very low power consumption.
Features
- Small package size
- Extended measuring range
- Reduced weight
- Low power consumption
- No insertion losses
Operation principle Open Loop O/L
The magnetic flux created by the primary current IP is concentrated in a magnetic circuit and measured in the air gap using a Hall device.
The output from the Hall device is then signal conditioned to provide an exact representation of the primary current at the output.
CLOSED LOOP CURRENT SENSORS (C/L)
Compared to the open loop sensors, Hall effect closed loop sensors (also called Hall effect "compensated" or "zero flux" sensors) have a compensation circuit that dramatically improves performance.
Features
- Wide frequency range
- Good overall accuracy
- Fast response time
- Low temperature drift
- Excellent linearity
- No insertion losses
Operation principle Closed Loop C/L
The magnetic flux created by the primary current IP is balanced by a complementary flux produced by driving a current through the secondary windings.
A hall device and associated electronic circuit are used to generate the secondary (compensating) current that is an exact representation of the primary current.
Hall Effect - Voltage Sensors Technologies
Closed Loop Voltage Sensors (C/L)
It is also possible to measure a primary voltage with galvanic isolation using the same LEM Hall Effect technology.
These voltage sensors are based on the more sensitive and accurate current measurement technologies, such as closed loop Hall effect designs.
The main difference from a current sensor is the addition of an internal primary winding with a large number of turns, allowing the sensor to create the necessary ampere-turns to measure the small primary current.
Features
- Measurement of high voltages
- Safety isolation
- Good overall accuracy
- Low temperature drift
- Excellent linearity
Operation principle Closed Loop C/L
A very small current limited by a series resistor is taken from the voltage to be measured and is driven through the primary coil. The magnetic flux created by the primary current IP is balanced by a complementary flux produced by driving a current through the secondary windings.
A hall device and associated electronic circuit are used to generate the secondary (compensating) current that is an exact representation of the primary voltage. The primary resistor (R1) can be incorporated or not in the voltage sensor.