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Aim Dynamics offers a wide variety of DC current sensors. Most DC current sensors operate using the Hall effect principle, which allows them to measure both DC and AC current. DC Hall effect current sensors are typically bidirectional, but can also be customized to only account for a single direction of flowing current. A Hall effect-based transducer is generally composed of a signal conditioning circuitry, a core, and a Hall effect device.
The current conductor travels through a magnetically pervious core that focuses the conductor’s magnetic field. The Hall effect device core is mounted at a right angle to the focused magnetic field. When the Hall device detects a magnetic field, it produces a potential voltage that is then amplified by the transformer it is attached to, into the output type desired by the user.
These DC Hall effect current sensors output a voltage, DC or AC, corresponding to the signal detected on the primary conductor. These are active sensing devices (they require external power).
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Split-Core vs. Solid-Core
Split-core Hall effect current sensors are convenient to install because they don’t require existing conductors to be disconnected in order to install.
However, solid-core Hall effect current sensors are more likely to contain closed-loop sensors. The feedback loop that closed-loop sensors provide means that these will have the best linearity, as well as the lowest temperature drift. While not exclusive to solid-core Hall effect devices, very few manufacturers have the capability and expertise to build split-core closed-loop Hall effect sensors.
Aim Dynamics sells open-loop and closed-loop Hall effect sensors in split-core and solid-core models.a
Open-Loop vs. Closed-Loop
CHall effect current sensors are available in either open or closed-loop. Open-loop sensors offer low insertion loss, fast response time, compact size, and accurate, low-cost sensing. Less expensive than their closed-loop cousins, open-loop current sensors are generally preferred in battery-powered circuits given their low-operating power requirements and small footprint features.
Closed loop sensors offer fast response, high linearity, and low-temperature drift. The current output of the closed-loop sensor is relatively immune to electrical noise. The Closed-Loop sensor is sometimes called a ‘Zero-Flux’ sensor because its Hall-Effect sensor feeds back an opposing current into a secondary coil, wound on the magnetic core to negate the flux produced in the magnetic core by the primary current. Closed-loop sensors are often the sensor of choice when high accuracy is essential.
While both types of sensors can be economical depending on the application requirements, open-loop sensors provide the best cost advantage in the high current ranges (over 100 A). They are also the smallest size and weight. They maintain constant power consumption, no matter the sensed current. The price advantage of open sensors may only be realized for applications where temperature variation can be restricted.
Closed-loop current sensors, on the other hand, are more suitable for commercial and industrial applications, where they are commonly found. These sensors have the highest accuracy at ambient and high temperatures. They are ideal for noisy environments and their output is easily converted to voltage.
Bipolar vs. Unipolar Power
Hall effect current sensors that have a bipolar output, e.g. +/- 5V, almost always require a bipolar power supply, e.g. +/-15 Vdc. There are a few ways around this – LEM, for example, provides a series of bidirectional sensors that operate on a +5Vdc power supply. This is achieved via the use of an offset in the output. For example, +2.5V might be the output at 0A on the primary. -100A might result in an output of 1.0V, and +100A would therefore have a 3.5V output. This “strange” output can often be handled by more advanced PLC units, or the output can be designed into a circuit.
Aim sells split-core DC sensing devices that require only a +12Vdc power supply. This is more convenient in systems where a +12Vdc power supply is all that’s available. See the AIMH040-xxxA-VT and AIMH020-xxxA-VT series for more information.
What is the difference between a Hall effect sensor and a traditional current sensor?
Hall effect current sensors can measure DC current in addition to AC current. They require active power in order to amplify their output into signals that are more suitable for monitoring and measuring use.
These devices are activated by an external magnetic field. We know that a magnetic field has two important characteristics: flux density, (B) and polarity (North and South Poles). The output signal from a Hall effect sensor is the function of magnetic field density around the device.
The output voltage, called the Hall voltage, (VH) of the basic Hall Element is directly proportional to the strength of the magnetic field passing through the semiconductor material (output ∝ H). This output voltage can be quite small, only a few microvolts even when subjected to strong magnetic fields, so most commercially available Hall effect devices are manufactured with built-in DC amplifiers, logic switching circuits, and voltage regulators to improve the sensor's sensitivity, hysteresis, and output voltage. This also allows the Hall effect sensor to operate over a wider range of power supplies and magnetic field conditions.
Why are these called Hall effect current sensors?
The effect of generating a measurable voltage by using a magnetic field is called the Hall effect after Edwin Hall who discovered it back in the 1870’s with the basic physical principle underlying the Hall effect being Lorentz force; to generate a potential difference across the device the magnetic flux lines must be perpendicular (90 degrees) to the flow of current and be of the correct polarity, generally a south pole.
The Hall effect provides information regarding the type of magnetic pole and the magnitude of the magnetic field. For example, a south pole would cause the device to produce a voltage output while a north pole would have no effect.
Are Hall effect sensors used in conjunction with some sort of DC Power Meter?
Yes. DC power meters exist, and they receive their current readings either from Hall effect sensors or from DC shunts. Often, these DC meters will have a configuration option that allows them to measure low currents directly, e.g. 0-5A. In these cases the meter either has a small Hall effect device built-in or it uses an internal shunt.
DC power meters can provide current readings, voltage readings, energy readings, and power readings. Unlike AC submeters, DC power meters typically measure a single conductor, given that there is no concept of phase in DC power.