DR. GYURCSEK ISTVÁN Mechanical Sensors 1. Sources and additional materials (recommended) Lambert Miklós: Szenzorok elmélet (ISBN 978-963-874001-1-3) Bp. 2009 Jacob Fraden: Handbook of Modern Sensors (ISBN 978-1-4419-6465-6) Springer NY. 2010 S. Tumanski:Principles of electrical measurement, CRC Press 2006. ISBN 0-7503-1038-3 Máté J.: Méréstechnika 1. PTE PMMIK, ERFP-DD2001-HU-B-01 Dr. Petróczky Károly: Bevezetés a nyúlásmérő bélyeges méréstechnikába, SZIE,Gödöllő http://gyurcsekportal.hu/mik.html 1 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Sensor Groups (THERM,EL,X) (RAD,EL,X) (MECH,EL,X) (MAG,EL,X) (CHEM,EL,X) Metal Resistors Photometers Force, Torque, Pressure Magnetoresistors Elecrochemistry Semiconductor NTC, PTC, pn Radiowave Detectors Position Detectors Galvanic- Magnetic Det. Humidity Detectors Thermocouples IR Sensors Flow Sensors Ionselective Detectors Thermal Switches Quant Detectors Speed Sensors Gas Detectors Accelerometers Acoustic Detectors 2 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Uncertainty of Strain Gauges Position Sensors Displacement Sensors Analogue Displacement Sensors Digital Displacement Sensors 3 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Force, torque, pressure sensors (piezo resistive usually) strain (deformation) change in resistance (1) Constantan (Cu:58%, Ni:42%) Low TEMP dependency, g = 2 (bélygállandó) (2) Silicon better sensitivity, but non-linear! Metal thread stamp : p semiconductor n semiconductor metal thread A A = 2με μ: Poisson factor Gauge factor (g) (gauge [geid3:] factor) 4 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauge Shapes (d) (e) (a) Push-pull (single-axis) (b) For torsional deformation (c) For 0-60-120 o tensions (d) X-Y deformation (simple) (e) X-Y deformation (complex) 5 gyurcsek.istvan@mik.pte.hu 2018.07.09.
transversally thicker for error reduction Strain Gauge Cell Never single stamp in practice Wheatstone-bridge cell Temp. compensation (see lab materials) 6 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Force and Acceleration Sensing strain gauge flexible rod strain gauge Comment: Instead of strain gauge piezoelectric sensor in accelerometers (next ) 7 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Piezoelectric Accelerometer Deformation (change in shape) Voltage ( NOT STRAIN GAUGE ) Piezoelectric disk Seismic mass mounted by pre-loaded spring (tuned) Electronics ICP (or IEPE) amplifier (Integrated Circuit Piezoelectric) (Integrated Electronics, PiezoElectric) ICP (R) trademark of PCB Piezotronics Inc. 8 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Uncertainty of Strain Gauges Position Sensors Displacement Sensors Analogue Displacement Sensors Digital Displacement Sensors 9 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauge Features and Errors Features Nominal stress max. allowed mechanical stress in operation range Lower operation limit min. mechanical stress for evaluable output Cell factor (sensitivity) U max U 0 U táp Errors mv Creep (kúszás) cell tracking with gauge block Repetition error different response for the same stress (resistance changes) Linearity error Low at metal thread Higher at semiconductors (polynomic characteristics = catalogue data) Temperature dependency (catalogue data) V 10 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauge Error Calculation Error Group 1 - proportional to stress Cell factor tolerance (h t ) Cell factor temp. dependency (h θ ) Creep (kúszás) (i.e. viscosity of glue) Repetition error (h rep ) Error Group 2 - stress independent Linearity error (h lin ) Temp. dept. null position (h 0 ) Example Determine the equivalent error of a two-cell series measurement system. Cell parameters are the followings: h 1 θ =4% h 2 θ =3,5% h 1 lin =2,5% h 2 lin =1,5% h 1 rep =3% h 2 rep =5%. Solution Correlation (equivalent error) Multiple cell connection (series / parallel) Error averaging h eq = h 2 θ + h 2 2 lin + h rep 11 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Uncertainty of Strain Gauges Position Sensors Displacement Sensors Analogue Displacement Sensors Digital Displacement Sensors 12 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Position Sensor GPS Position sensor (in general) Passive usually (third Miller-index = el ) Reference point required ( origin ) GPS system (example) Spherical coordinate system Local ref. point ( origin ) Greenwich X Equator Example: Hungary N 43 o, E 19 o 13 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Uncertainty of Strain Gauges Position Sensors Displacement Sensors Analogue Displacement Sensors Digital Displacement Sensors 14 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Analogue Displacement Sensors Potentiometer Coal bed potentiometer (wear ( kopik ) noisy ) Wire potentiometer (constantan: Cu-Ni) Inductive displacement sensors (i.e. LVDT) Synchro transmission (i.e. SELSYN) Magneto strictive sensors Magneto static sensors Magneto resistive sensors Galvanomagnetic sensors Capacitive sensors Radiative sensors Ultrasound Microwave Light radiation PSD (Position Sensing Diode) 15 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Potentiometers Effect diagram of potenciometer Model and static characteristics of wire potmeter x, y, z MECHANICS R ATTENAUT. SWITCH U out Slider at position B causes one-round short circuit R/N step in resistance. θ U source Principle of wire potenciometer 16 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Potentiometer Static Characteristics 17 gyurcsek.istvan@mik.pte.hu 2018.07.09.
LVDT (Linear Variable Differential Transformer) Inhomogeneous magnetic field L = L(x,y,z) non-linearity! Passive inductor (for end position detecting only) Transformer sensors (bridge or differential transformer better linearity!) 18 gyurcsek.istvan@mik.pte.hu 2018.07.09.
LVDT small is all linear 19 gyurcsek.istvan@mik.pte.hu 2018.07.09.
LVDT 20 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Selsyn (or Synchro) 1 SELf SYNcronous machine Angular data transmission bw. remote points Electro-mechanical device 21 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Selsyn (or Synchro) 2 Angle dept. seconder (S) voltages... RX V TX S = V cos, V RX S = V cos β Resting position α = β V TX S = V RX S I S = 0 Rotation balancing currents synchronising torque α β V TX S V RX S I S 0 β TX Synchronising torque M TX = M RX = M m sin ε ε = α β Load dependent tracking error ε 0 near linear in small 22 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Strain Gauges Uncertainty of Strain Gauges Position Sensors Displacement Sensors Analogue Displacement Sensors Digital Displacement Sensors 23 gyurcsek.istvan@mik.pte.hu 2018.07.09.
End Position Switch Classification Mechanical contact (reed relay) Conductive liquid Inductive position sensor (switch!) Capacitive position sensor (switch!) Magnetic position switch Photo-electric switch Pyroelectric switch Ultrasonic switch Microwave switch Radioactive radiation limit sensor Reed kapcsoló contact (or (vagy relay) relé) Moving contact Standing contact IDEAL SWITCH protective gas magnetic principle rod: elastic steel contact: Cu, Ag Drawbacks low speed (khz!) hysteresis contact stuck lifetime 24 gyurcsek.istvan@mik.pte.hu 2018.07.09.
Questions 25 gyurcsek.istvan@mik.pte.hu 2018.07.09.