Experimental methods - KTS€¦ · • Magnetostrictive sensor • Inductive sensors • Inductosyn...

transcript

Experimental methodsSensors of displacement and its derivation

07/10/2016 KTS/EXM1 - Sensors of displacement and its derivation1

Source: www.honeywell.com

Position sensors with discrete signal

Limit Switches (contact)

Position sensors with discrete signal

Inductive proximity sensors (non-contact)

Main technical parameters:

Operating voltage

Operating current

Assured operating distance

Max. switching freq.

hystereis

Protection

Switching output (PNP x NPN)

Balluf induction sensor

Hall effect sensors (non-contact)

mT,A,,CmV; * 1-3

A hall effects sensor is a transducer

that varies its output voltage in

response to a magntic field.

where RH is Hall materiál constant

d is the semi-conductor thickness

in the direction of magnetic flux density B

Hall effects sensors are used for proximity switching, positioning, speed detection, and current sensing applications.

Hall effect sensors (non-contact)

Differencial layout of the hall effect sensor

– linearization of the voltage/distance characteristic

BkUH *

xfkBkU

and nonlinear

Examples of usage of Hall effect sensors

Speed hall effect sensor, XS 06A905161B, Skoda Octavia

Hall effect sensor TLE4905L: 3÷24V, 40÷+150°C, P-SSO-3-2, 3x4x1,5mm

Other sensors type of position with discontinous signal

• Optical sensors

• Ulstrasonic sensors

• Laser sensors

• Capacity sensors

Displacement sensors with continous signal

• Potentiometer

• Magnetostrictive sensor

• Inductive sensors

• Inductosyn (Linear encoder)

• IRC (Incremental Rotary Encoder)

Potentiometer

Source: www.electronics-tutorials.ws

Potentiometer

Resistive sensor of displacement

Advantages:• Absolute values in the whole measuring range• Simple construction – inexpensive

Disadvantages:• Output voltage singal• Low reliability (lifespan)• Temperature dependancy• Output signal noise

Magnetostrictive sensor of displacement (continous output signal)

Advantages:• Absolute values in the whole measuring range• Simple construction – inexpensive

Disadvantages:• Output voltage singal• Low reliability (lifespan)• Temperature dependancy• Output signal noise

Magnetostrictive sensor of displacement

A - electrical signal is initialised in the magnetostrictive wire, B – current pulse and magnetic fieldexcitates a mechanical impulse - strain (Viedemann effect) in magnetostrictive material, the excitedimpulse is propagating along the wire and detected in the induction pickup coil. Position of magnet (measured quantity) is evaluated from the time between the initial signal and reflectected pulse. (elasticwave in ferromagnetic material v=3000 m/s)

Source: www.electronics-tutorials.ws

Magnetostrictive sensor of displacement

Technical parameters:• Measuring lenght – segments up to 7 600 mm (standard

50 up to 1 500 mm)• System resolution – min 10 μm • Repeatibility – min 20 μm• Sampling rate – 1 up to 10 kHz• Output signal - absolute

http://www.balluff.com/balluff/MDE/en/products/overview-micropulse-transducers.jsp

Inductance displacement sensor

Inductive displacement sensor

Example of inductve displacement sensor WA 200 (Hottinger Baldwin Messtechnik)

Stroke: 200 mm

Input signal: 80 mV / V

Supply voltage and frequency: 2,5 Vef / 4,8 kHz

Linearity tolerance: 0,2 %

Maximal acceleration: 2 500 m/s2

Weight: 130 g

Inductive encoders:• Inductosyn (linear displacement)• Resolver (angular displacement)

Measured element that is connected to a rider with 2 coils (mutualy shiftedof 0,25 loop) is sliding above a static scale. Riders coils are supplied with AC voltage with 90o phase shift.

tkUtutkUtu cos and sin 1211

Due to the magnetic flux induction voltage in the static slace is:

tkUttkUtututu coscoscossinsin12112

Inductosyn (measuring of linear displacement)

Resolver – measuring of angular displacement

tUtu sin

tkUtu sin

Advantages:• High precision• High Measuring Stroke (in the lenght of CNC machine)• Independancy on distance change of scale and rider• Reliable for dusty environment

Disadvantages:• Cyclical absolute measruement (referent positioning

required)• Electronic for the step counting required

Optical rotary encoders:• Incremental encoders (relative angular displacement)• Absolute position encoders (absolute angular displacement)

IRC sensor – measuring of relative angular displacement

• Measurable valuesPosition (turning angle) – Relative

Rotation speed

• Principle of functionOptical (contactless switches)

Output: logic signals

• UsingCNC machines

Industry automatization

Laboratory experiments

IRC sensor – measuring of angular displacement

• Two pairs of LED diodes + phototransistors

• Light beam chopped by rotary disk

• 90° phase shift between output signals A, B

IRC sensors are mainly used for the angular velocity measurement (given by

pulse frequency)

Relative angular position (given by pulse count – requires indexing of the

output pulse-signal)

Direction – given by phase difference

CW – A leads B

CCW – B leads A

Absolute Postion Encoder – measuring of absolute angular displacement

• Measurable valuesPosition (turning angle) – Absolute

Rotation speed

• Principle of functionOptical (contactless switches)

Output: logic signals

• UsingCNC machines

Industry automatization

Laboratory experiments

Velocity sensors

linear:

– inductive - electromagnetic (with movable magnet)

– inductive - electrodynamic (with movable coil, appropriate for measuringof vibration – NOT FREQUENCY)– laser – ultrasonic– incremental (inductosyn in the speed measuring mode – measure of theoutput pulse frequency)

angular:

– DC tachogenerators (AC tachogenerators)– stroboscope– incremental ( IRC in the speed measuring mode – measure of the output pulse frequency)

The laser vibrometer serves for contactless and very fast measuring of vibrations. The output of the laser vibrometer is a signal of vibration velocities. It operates at a distance up to 3 meters from the monitored object.

Laser Doppler Vibrometer

Laser vibrometer Brüel & Kjær 8338 and its adjustement

Acceleration sensors

3 basic types of acceleration sensors:

- Piesoelectric

(appropriate for measuring of vibration, unable to measure static acceleration)

- Piesoresistive

( Accelarated mass pressure exerted on a piezoresistor the resistivity varies accordingly. Capable ofmeasuring of static accleration)

- Capacity

(Evaluation of the capacity of two plates affected by the acceleration

The principal function of acceleration sensors is based on the 2. Newton´s Law(applying a force F on mass m): F = m * a

Mechanical dynamic system:

m - mass of the coil („seismic mass“)

M - sensor cover – connected with

measuring object

b - damping (depending on velocity

(viscouse damping)

k - spring stiffness

u - induced voltage

Piesoelectric sensors of acceleration

– Use of piesoelectrical crystal for generation of electric charge as an results

of mechanical stress.

– Pair of piesoelectric elements are used for higher precision.

– Material damping of piesoelectric material is very low, enabling to measure

vibration up to 3*104 Hz.

Inductive (electrodynamic) sensors of acceleration

– Based on system motion, coil vibration in the magnetic field of permanent

magnet induces voltage in the coil that is function of velocity

– The resonance frequency of electrodynamic sensors is in the range of 5-10 Hz

– If additonal damping (damping element placed below the coil) the frequnecy

can be in the range 1 – to 3000 Hz

1- measuring coil, 2- damping coil, 3- core of magnetic system, 4- permanent magnet, 5- membrane

Capacity sensors of acceleration

– Capacity sensor MEMS (Micro-Electro-Mechanical-System)

Ancors – connection with vibration objectMain beam – Seismic massCell – Differential capacity sensor

C – capacity capacitor (F) ε0 – permitivity of vaccum (= 8,859. 10-12 F/m)

ε - relative permitivity of dielectricum (-) S – plates area (m2)

d - plates distance (m)

Experimental methods - KTS€¦ · • Magnetostrictive sensor • Inductive sensors • Inductosyn...

Documents