Current Sensors

ECE 5230 Mechatronics Assignment 1

Larry Ballard

Outline

• References• To Explore Further• Principle Applications• Current Sensor Designs

– Resistive Current Sensor– Hall Effect Current Sensor– Magneto-Resistive Current Sensor– AC/DC Current Transformer

• Sample Configuration• Where to Buy

References

• http://www.sensorsmag.com/sensors/article/articleDetail.jsp?id=358200

• http://www.bergoz.com/products/IPCT/IPCT-downloads/files/IPCT.11flyer.PDF

• http://www.sypris.com/library/documents/NT-Datasheet.pdf

To Explore Further

• http://adweb.desy.de/mdi/CARE/Lyon/Lyon%20DCCT_Technology_Review.pdf

Principle Applications

• Actuator failure detection• Measure energy consumption

– Electric/Hybrid cars/Electric motors etc.

• Contamination Detection– Air/Water filters etc. (Greater current with higher

contamination)

• Circuit failure detection• Solar Technology• Welding Equipment• Building Control and Automation

Current Sensor DesignsResistive

The idea behind the resistive current sensor is that a very small resistance is placed in series with the circuit where the current is to be measured. The voltage across the resistor is then amplified and measured.

This current sensor is not of much use today except in very high current systems. They are generally a shunt fabricated out of brass to have a voltage drop of 50 mV for a specific current.

One positive point for the resistive current sensors is that they work very well at DC. Also they can be made very cheeply

Current Sensor DesignsHall Effect

Hall Effect current sensors are shaped like a doughnut and you pass the wire you wish to know the current of through the hole. Their output is proportional to input, DC or AC. They are subject to zero drift due to stray magnetic fields. There is no voltage drop associated with them unlike the resistive current sensors

Current Sensor DesignsHall Effect

Hall sensors measure the magnetic field surrounding the conductor. They can sense DC and AC currents. A circular core of soft magnetic material is placed around the conductor to concentrate the field. The Hall element, which is placed in a small air gap, delivers a voltage that is proportional to the measured current. This sensor also offers a galvanic isolation.

There are open loop and closed loop sensors. The open loop sensors are cheaper but you pay in precision.

Current Sensor DesignsHall Effect

Advantages of the Hall effect sensor design are the fact that it doesn’t need to be part of the circuit that it is measuring. It also is capable of measuring a very wide range of current frequencies including DC.

Disadvantages of this design are the fact that it is rather large and has to fit somehow into the project.

Current Sensor DesignsMagneto-resistive

Magneto-resistive sensors are based on the magneto-resistive effect. They can be packaged very small and have a very wide measurement range. Magneto-resistive sensors are able to measure AC, DC and impulse currents from a few milli-amperes to 150 A. Also as with the Hall Effect sensors the input current is isolated from the output.

Current Sensor DesignsMagneto-resistive

The operating principle of the Magneto-resistive current sensor is based on a differential magnetic field measurement with compensation. The primary current is fed through a U-shaped conductor, creating a field gradient between the two sides of the conductor. The thin film magneto-resistors are placed on a silicon chip and connected to a Wheatstone bridge. A current is fed back through the sensor. The resulting field exactly compensates the other field so that the sensor always works around a single operating point.

Current Sensor DesignsMagneto-resistive

The biggest advantage of these sensors is their size. They are fabricated as ICs. These sensors can also be fabricated cheaply.

Common Specifications

• Response time

• Sensitivity

• Magnetic Offset Error

• Package

Where to Buy

http://www.ttiinc.com/page/home

http://www.digikey.com

http://www.national.com