ECE5320 Mechatronics Assignment #1: Literature Survey on Sensors Through Loop Current Sensors

1. ECE5320 MechatronicsAssignment #1: Literature Survey on Sensors Through Loop Current Sensors Prepared by: Robert Silver Dept. of Electrical and Computer Engineering Utah State University E: ; T: (435)797-; F: (435)797-3054 (ECE Dept.) Website: http://mechatronics.ece.usu.edu/ece5320/ 3/10/2006

2. Outline for Show • Reference sources • To probe further • Sensor description • Basic working principal • Different types • Examples • Pros and cons of each type • Choosing correct sensor for different applications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference Sources • http://content.honeywell.com/sensing/prodinfo/current/ • http://www.allegromicro.com/ Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuitby: Richard Dickinson & Shaun Milano • Current Sensing in Electric Drives A Future and History Based on Multiple Innovationsby: Eric FAVRE ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further Internet sites to find sensors at: Honeywell: http://content.honeywell.com/sensing Allegro Microsystems http://www.allegromicro.com GMW: http://www.gmw.com/electric_current/currmeas.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Though Loop Current Sensors http://content.honeywell.com/sensing/prodinfo/current/ Type: Sense Resistor and Hall Effect, Open and Closed Loop Linear ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Basic Working Principal: Provides a linear output voltage that tracks the waveform of the sensed current. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Sense Resistor Type • Sense resistors are simply a resistor placed in series with the load. By ohms law, the voltage drop across the device is proportional to the current. • For low currents these devices are accurate when the resistance values have a tight tolerance. • Also require other components to give appropriate output, such as amplifiers to modify and enhance the signal out. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Hall Effect • “According to the Hall effect, a magnetic field passing through a semiconductor resistor will generate a differential voltage proportional to the field” • Figure 1: Representation of the Hall effect in 3d “Concentric magnetic field lines are generated around a current carrying conductor. Approximating the primary current conductor as infinitely long, the magnetic field strength may be defined B = µoI/ 2pr, where µo is the permeability of free space, I is the current and r is the distance from the center of the current conductor.” Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Current Transformer Type Current carrying conductor Sense resistor By Faradays law, the current in the conductor going through the loop sensor will generate a magnetic field in the secondary coil of the loop sensor. The current induced in the secondary coil is proportional to the number of turns in the coil. This current is then sensed by a sense resistor and converted into a voltage, which is the output of the sensor. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Open Loop Hall Effect Type Hall effect semiconductor Current carrying conductor For an open loop design using Faradays Law the Hall Effect device output is amplified and sent out as a voltage that is a scaling factor of the sensed current of the I-primary in the wire through the toriod. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Open Loop Hall Effect Type Hall effect semiconductor Current carrying conductor This open loop design doesn’t have a feedback control loop and is therefore subject to some errors caused by eddy current errors and collapsing magnetic fields due to varying current draws caused by, for example, the varying magnetic fields in an electric motor. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Open Loop Application http://www.ssac.com Here an open loop current sensor is used to start a fan whenever the oven is on. This also shows how a through hole type current sensor is advantages, because it’s output and control voltages are separate from the rest of the high voltage circuit being sensed. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Open Loop Hall Effect Pros and Cons Pros:Very low power consumption Small weight and size for high current sensing abilities Resistant to current overloads No break in main line when sensor installed and used Fairly inexpensive Cons: Moderate bandwidth, response time Larger temperature dependence for measurement accuracy High frequency eddy-current losses ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Closed Loop Hall Effect Type For this closed loop type current sensor it uses the output of a Hall device that drives a secondary coil and this will make a magnetic field to cancel the primary current field induced by Faradays law into the coil by I-primary. The secondary current is then measured as a voltage across a sense resistor and before that scaled to the primary current by its secondary coil ratio. The resultant scaled voltage across the sense resistor is Vout. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Closed Loop Hall Effect Type When the addition of the two fields is zero, the potential errors with the offset drift, sensitivity drift, and the saturation in the magnetic core will be canceled out. These type of Hall effect sensors offer the fastest response times but do drive a secondary current carrying coil that can use up to several milli-amps and so the power consumption is much higher than for the open loop type. Isolated Open Loop Current Sensing Using Hall Effect Technology in an Optimized Magnetic Circuit Richard Dickinson & Shaun Milano ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Closed Loop Hall Effect Pros and Cons Pros: High linearity and accuracy Low change in characteristics with respect to temperature No insertion loss in the primary circuit A robust design for EMI Excellent high frequency response, often surpassing 100kHz Cons: Higher power consumption than an open-loop sensor Larger physical size for high current applications Higher cost than open-loop designs ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Closed Loop Motor Control Example Current sensor being used as a scaled input to adjust the gain on the driver chip and a feedback to the microcontroller ship to be incorporated with the feedback from the other sensors in order to drive the motor at the desired speed. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Current Sensor Hookup Normal Wiring Scheme: • Offset dc voltage (also acts as the power source) • This offset voltage should be from an isolated dc power source to prevent voltage variations for the dc offset voltage as that will directly effect the sensed current output voltage. • Zero potential voltage • Current sensor output to controller or a/d recorder (Vout = offset dc voltage + sensed and scaled current output) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Picking a Sensor Deciding Variables • What is the maximum current that could be going through the sensed wire • How much money can your budget allow • Accuracy of sensor • Frequency response of sensor needed for primary wire power variations • Ambient surroundings sensor will be operating in • Amount of filtering required for desired output accuracy ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. More Applications Industrial- Through hole current sensors are used extensively in industrial motor control, power monitoring, control applications of all types Circuit boards- Small through hole current sensors are used on circuit boards in many applications for also sensing small currents Automotive- The Toyota Prius battery back has a built in through hole current sensor to monitor the power dissipation to its electric motor and generators ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators