MSD Assignment

8/3/2019 MSD Assignment

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Mechatronics Systems Design Assignment

Nanda Kishore M R

09M206

V Semester

October 25, 2011


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Contents

0.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30.2 Measurand: Acceleration . . . . . . . . . . . . . . . . . . . . . . . 3

Capacitive Accelerometer . . . . . . . . . . . . . . . . . . . . . . 3ADXL330 Accelerometer . . . . . . . . . . . . . . . . . . . . . . . 4

0.3 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.4 Measurand: Angular Position and Speed . . . . . . . . . . . . . . 7

Hall Effect Rotational Speed Sensor . . . . . . . . . . . . . . . . 7Honeywell SS461A sensor . . . . . . . . . . . . . . . . . . . . . . 8Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

0.5 Measurand: Temperature . . . . . . . . . . . . . . . . . . . . . . 10Integrated Circuit Temperature Sensor . . . . . . . . . . . . . . . 10LM35 Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . 12Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

0.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

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List of Figures

1 Types of Capacitive Accelerometers . . . . . . . . . . . . . . . . 42 Principle of ADXL330 Accelerometer . . . . . . . . . . . . . . . . 43 ADXL330 Signal Conditioning . . . . . . . . . . . . . . . . . . . 54 Application of ADXL330 Accelerometer . . . . . . . . . . . . . . 65 Hall Effect Principle . . . . . . . . . . . . . . . . . . . . . . . . . 76 Simple Hall Effect sensor . . . . . . . . . . . . . . . . . . . . . . . 87 Signal Conditioning Block Diagram of SS461A . . . . . . . . . . 98 Application of Hall effect Angular Position Sensors in Brushless

DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Linearity of Silicon Temperature Sensors . . . . . . . . . . . . . . 1110 The LM35 Temperature Sensor . . . . . . . . . . . . . . . . . . . 1211 IC Temperature Sensor used in PC cooling fan system . . . . . . 13

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(a) Single Capacitor type (b) Differential Capacitor type

Figure 1: Types of Capacitive Accelerometers

ADXL330 Accelerometer

The ADXL330 is a product of the company Analog Devices. It is a small,thin, low power, complete 3-axis accelerometer with signal conditioned voltageoutputs, all on a single monolithic IC. It measures acceleration with a minimumfull-scale range of 3 g. It can measure the static acceleration of gravity intilt-sensing applications, as well as dynamic acceleration resulting from motion,shock, or vibration.

Working

The sensor is a polysilicon surface micromachined structure built on top of asilicon wafer. Polysilicon springs suspend the structure over the surface of thewafer and provide a resistance against acceleration forces. Deflection of thestructure is measured using a differential capacitor that consists of independentfixed plates and plates attached to the moving mass. Acceleration deflects themoving mass and unbalances the differential capacitor resulting in a sensoroutput whose amplitude is proportional to acceleration.

Figure 2: Principle of ADXL330 Accelerometer

Signal Conditioning

The sensor has in-built signal conditioning circuitry to implement an open-loop acceleration measurement architecture. Since the voltage change is small,it requires amplification and further conditioning so that it can appreciably

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utilized. One main advantage of the ADXL330 sensor is that quantization errorsand temperature hysteresis are negligible as there is no additional circuitry

required for temperature compensation. The block diagram is provided in thefollowing page.

Figure 3: ADXL330 Signal Conditioning

Specifications

The important specifications of the accelerometer are given below:Measurement range: Minimum = 3 gNonlinearity: 0.3% of full scaleSensitivity: 300 mV/gSensitivity change due to temperature: 0.015 %oCFrequency Response: Bandwidth: X and Y: 1600 Hz ; Z: 550 HzSensor resonant frequency: 5.5kHzPower Supply: Voltage = 1.8 3.6 V ; Current = 320 A at 3VOperating Temperature Range = -25 - +70 oC

0.3 ApplicationsCapacitive accelerometers are used in a wide range of applications. AutomotiveApplications include uses in Antilock Braking systems, Traction Control Sys-tems, Vehicle Dynamics Control, Electronically Controlled Suspension, TyrePressure Monitoring, etc. They are also used for tilt monitoring in mobile

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phones, monitoring the health condition of patients, seismic monitoring, incli-nometer instruments, biomedical applications and many other applications.

The ADXL330 accelerometer, more specifically, is used to measure the res-piration of patients. It is mounted on the back side of the ECG electrode clip.It detects the rise and fall of the chest due to respiration and adjusts for patientmovement. It is immune from other medical equipment leakage currents andpoor electrode connections that can create measurement interference. This situ-ation is particularly a problem in environments where multiple pieces of medicalequipment are hooked up simultaneously to the patient.

Figure 4: Application of ADXL330 Accelerometer

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0.4 Measurand: Angular Position and Speed

Sensing of rotational speed becomes important in many applications where anactuation is to be performed based on the amount or speed of rotation of acertain component. In these applications, rotational speed sensors are used.

A rotational speed sensor is a type of tachometer which reads the speed ofrotation of a wheel. Most of these sensors give their output as voltages. Toachieve this, a number of transduction effects may be utilized. Some of thecommonly used ones are Inductive, Magnetoresistive and Hall effect. In thisreport, the Hall effect rotational speed sensors will be discussed.

Hall Effect Rotational Speed Sensor

Hall Effect occurs when a strip of conducting material carries current in thepresence of a transverse magnetic field. This results in the generation of a

potential perpendicular to both the magnetic field and the electric current.Hall effect sensors can be used as analog motion sensing devices. When a

change in the magnetic field or the electric current flowing through the conductoroccurs, the output voltage varies, thus producing the transduction.

Theory

Consider a thin sheet of semiconductor material through which current is passed.When no magnetic field is present, current distribution is uniform and no po-tential difference is seen across the output. But, when a perpendicular magneticfield is present, a Lorentz force is exerted on the current. This force disturbsthe current distribution, resulting in a potential difference (voltage) across theoutput. This voltage is the Hall voltage (VH).

Figure 5: Hall Effect Principle

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In a simple Hall effect sensor, the Hall element through which current ispassed is present. The magnetic field is applied by means of an electromagnet

or a permanent magnet which is external to the sensor housing. In a rotationalspeed measuring application, the magnet used is a permanent ring magnet. Thisring magnet is rotated with the shaft whose rpm is to be measured. The Halleffect sensor is fixed in close proximity and radially to the ring magnet so thatthe magnetic field lines are strong enough to produce the Hall voltage. As thering magnet rotates with the motor, its south pole passes the sensing face of theHall sensor with each revolution. The sensor is actuated when the south poleapproaches the sensor and deactuated when the south pole moves away. Thus,a single digital pulse will be produced for each revolution.

Figure 6: Simple Hall Effect sensor

Honeywell SS461A sensor

The SS461A sensor, a product of Honeywell, is a latching Hall effect digitalposition sensor. It is used to latch the output states like bipolar switches anduses both positive and negative magnetic field, such as that from a ring magnet.This sensor can be used in rotary position or speed sensing applications.

Specifications

Supply voltage = 3.8-30 VMagnetic Actuation type: Bipolar latchOperating Temperature Range: -40oC to 150oCOutput Voltage = 0.4V maxSupply current = 7.5 mA

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Output current = 20 mA

Signal Conditioning

The signal conditioning circuitry in built in the SS461A sensor contains tem-perature compensation circuitry so that a thermally balanced integrated circuitover the full temperature range is achieved. It also provides band gap regulationresulting in extremely stable operation. In addition to these, it has the basicsensor requirements like the voltage regulator, amplification circuitry, etc. Thebasic diagram is given below.

(a) Analog (b) Digital

Figure 7: Signal Conditioning Block Diagram of SS461A

ApplicationsHall Effect sensors find applications wherever ferrous elements are involved andmagnets can be incorporated. They are widely used for position sensing, geartooth sensing, current sensing, mechanically operated solid state switches, ve-locity sensing, etc. In this section, a specific application in which the rotationalspeed has to be sensed is discussed.

In the manufacturing industry, a Hall Effect rpm sensor is used in brushlessDC motors. Brushless DC motors are essentially brush-type motors turnedinside out. Power is fed directly to the armature windings while a permanentmagnet rotor is the rotating member. This can be either an inner or outerrotating member, depending on the motor design. The brushes and commutatorof a DC motor are replaced by position sensors and electronic switching.

In brushless motors, a Hall effect position sensor senses the position of therotating magnet and excites the proper windings through logic and driver cir-cuitry. Three Hall effect sensors are used for effective operation. The rotatingpermanent magnet moving across the front of the sensor causes it to changestate. When each south pole passes the sensor, the sensor operates. The fol-lowing figure shows the detailed operation of the sensor system.

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Figure 8: Application of Hall effect Angular Position Sensors in Brushless DCMotors

0.5 Measurand: Temperature

Temperature is one of the most common measurands that is encountered in the

industry. Temperature sensing becomes a crucial part in an automated systembecause of the significant effect it can have on materials and processes in themolecular level. Temperature sensors sense changes in the temperature of asystem so that a suitable actuation can be performed. These sensors detecta change in a physical parameter such as resistance or output voltage thatcorresponds to the temperature change.

The most commonly used temperature sensing techniques are RTDs, ther-mocouples, thermistors and sensor ICs. The choice depends on the requiredtemperature range, linearity, accuracy, cost, features, and ease of designing thenecessary support circuitry. In this report, IC temperature sensors are discussed.

Integrated Circuit Temperature Sensor

Theory

The Integrated Circuit temperature sensor is a silicon bandgap based temper-ature sensor that is very commonly used in electronic equipment. It works onthe principle that the forward voltage of a silicon diode is temperature depen-dent. So, when the temperature varies, the forward voltage of the diode also

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Figure 9: Linearity of Silicon Temperature Sensors

varies. Therefore, this type of temperature sensor is sometimes referred to asthermodiode.

When the temperature of doped semiconductors changes, the mobility oftheir charge carriers changes and this affects the rate at which electrons andholes diffuse across a p-n junction. Thus, when the p-n junction has a potentialdifference V across it, the current I through the junction is a function of tem-perature. If we keep the current constant, the voltage becomes a function oftemperature. This concept is made use of in an IC temperature sensor and the

required transduction is obtained.This type of sensors are limited to applications where the temperature iswithin a range of -55oC to 150oC range. They generally come with in-built signalconditioning circuitry. They have the added advantage that no linearizationor cold-junction compensation is required. The following graph compares thelinearity of thermistors and thermodiodes.

Equation

The IC temperature sensor is based on the following equation:

VBE : Base Emitter VoltageT : Absolute Temperature

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LM35 Temperature Sensor

LM35 Temperature sensor is a product of National Semiconductor. It is a threeterminal device that produces output voltages proportional to the temperature.It is an analog sensor that is calibrated directly in Celsius, thus making it easierto use. It does not require any external calibration or trimming and maintainsan accuracy of +/-0.4 oC at room temperature and +/- 0.8 oC over a range of0 oC to +100 oC. A standard LM35 sensor and its equivalent circuit are givenbelow.

(a) Sensor (b) Equivalent Circuit

Figure 10: The LM35 Temperature Sensor

Specifications

Supply Voltage = +35V to 0.2VOuput Voltage = +6V to 1.0VOutput Current = 10 mAOperating Temperature Range = 55C to +150CAccuracy = 0.2 at room temperatureSensitivity = 10mV/oCNon- linearity = 0.3

Applications

Integrated Circuit Temperature Sensors are widely used in electronic equipmentfor monitoring the temperature providing the signal for any required compen-sation operation. One such example is the use of these sensors in the CPU ofpersonal computers to detect the temperature and accordingly turn on or turnoff the cooling fan.

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Recent generations of personal computers dissipate a lot of power, whichmeans they tend to run hot. The microprocessor and the hard disk drive are

notable hot spots. Cooling fans help to keep heat under control, but if a fan fails,or if ventilation paths become blocked by dust or desk clutter, the temperatureinside a computers case can get high enough to dramatically reduce the lifeof the internal components. High-performance personal computers and serversuse temperature sensors on their motherboards to monitor system temperaturesand avert system failure. The sensor senses the system temperature and turnsa cooling fan on when the sensors temperature exceeds a preset value. Thefollowing circuit shows a simple temperature sensor operated PC fan.

Figure 11: IC Temperature Sensor used in PC cooling fan system

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0.6 Conclusion

In this report, we have seen the principle, working and application of threetypes of sensors used to sense three different measurands. There are numerousother measurands which are encountered regularly in the industry. Keepingthis in mind, the complexity of any automatic mechatronic system can be com-prehended. The three measurands discussed, viz. Acceleration (Vibration),Angular Position and Temperature, are some of the most important and cru-cial measurands in most systems. One transduction effect for each of thesemeasurands has been discussed.

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0.7 References

Acceleration, Shock and Vibration Sensors, Newnes Sensor TechnologyHandbook, Dec. 2004

Small, Low Power, 3-Axis 3 g i MEMS Accelerometer ADXL330, Datasheetby Analog Devices

Patient Respiration Measurement using a 3-Axis Accelerometer, Resourcesfrom www.analog.com

Sensors and Transducers, Mechatronics System Design, Devdas Shettyand Richard Kolk, 1997

Honeywell Datasheet SS461A

Honeywell Application Note Low Gauss Bipolar Effect Sensors Hall Effect Sensing and Control, Honeywell Application Note

LM35 Precision Centigrade Temperature Sensors, Datasheet by NationalSemiconductor, Nov 2000

National Semiconductors Temperature Sensor Handbook

Sensors and Transducers, Mechatronics, W. Bolton

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