Measuring Networks 1

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1 DR. GYURCSEK ISTVÁN Measuring Networks 1 Sensor Circuits Sources and additional materials (recommended) Lambert Miklós: Szenzorok elmélet (ISBN ) Bp Jacob Fraden: Handbook of Modern Sensors (ISBN ) Springer NY S. Tumanski:Principles of electrical measurement, CRC Press ISBN Máté J.: Méréstechnika 1. PTE PMMIK, ERFP-DD2001-HU-B-01 Dr. Petróczky Károly: Bevezetés a nyúlásmérő bélyeges méréstechnikába, SZIE,Gödöllő gyurcsek.istvan@mik.pte.hu

2 Structure of Measuring Circuit Device Interconnection Signal source TX (ie. sensor) Signal transm. (ie. test lead) Receiver RX (ie. meas. device) Classification of signal sources / transducers Impedancie aspect Asimmetric Simmetric Grounding aspect Grounded Ground-independent Grounded w. GND offset Source model aspect Voltage source Current source 2 gyurcsek.istvan@mik.pte.hu

3 Signal Source (TX) Models Signal Receiver (RX) Models TX-RX Interconnections Noisy Signals, Noise Reduction Grounding, Earthing Solutions 3 gyurcsek.istvan@mik.pte.hu

Asymmetric Signal Sources Z in Z in Z in output output output

GND and terminals Asymmetric ground-indept.

4 Asymmetric Signal Sources Z in Z in Z in output output output Asymmetric grounded One terminal is grounded Different impedances bw. GND and terminals Asymmetric ground-indept. Insulated terminals from GND One terminal can be on GND Different impedances bw. GND and terminals Asymmetric grounded with GND offset Neither terminal can be grounded Different impedances bw. GND and terminals 4 gyurcsek.istvan@mik.pte.hu

Symmetric Signal Sources Z in Z in Z in Z in output Z in output Z in

impedances bw. GND and terminals Symmetric ground-indept.

common point and terminals Symmetric grounded with GND offset Neither

5 Symmetric Signal Sources Z in Z in Z in Z in output Z in output Z in output Symmetric grunded Neither terminal can be grounded Same impedances bw. GND and terminals Symmetric ground-indept. One terminal or common point can be grounded Same impedances bw. common point and terminals Symmetric grounded with GND offset Neither terminal can be grounded Same impedances bw. GND and terminals 5 gyurcsek.istvan@mik.pte.hu

6 Typical Transducer Errors Offset (zero point) error input indept. (constant) output component Calibration error difference bw. ideal and actual characteristic Linearity error - difference bw. reference line and actual characteristic Resolution the smallest increase step of the transducer Hysteresis error input direction dependent output Phase error phase difference bw. input and output signals Temperature error temperature dependent output signal Load error load (impedance) dependent output signal X out X in 6 gyurcsek.istvan@mik.pte.hu

7 Signal Source (TX) Models Signal Receiver (RX) Models TX-RX Interconnections Noisy Signals, Noise Reduction Grounding, Earthing Solutions 7 gyurcsek.istvan@mik.pte.hu

Asymmetric Receivers Housing Housing Parasitic capacitances Z in input Z in U out output

outputs and housing are on GND Different impedances bw.

, shielded 1 One output and housing on GND One input GND-indept.

8 Asymmetric Receivers Housing Housing Parasitic capacitances Z in input Z in U out output input U out output U output out Z in Shielding Shielding Asymmetric grounded One of inputs, outputs and housing are on GND Different impedances bw. GND and input terminals Asymmetric GND-indept., shielded 1 One output and housing on GND One input GND-indept. shielding Isolated inputs from GND, outputs, housing If one input is on GND different impedances bw. GND and input terminals Asymmetric GND-indept., shielded 2 One of outputs and housing are on GND Shield (Guard) is GND-indept. (floating) Input is GND-indept. (floating) High (parasitic) impedance bw. (H) and (G) Low (parasitic) impedance bw (L) and (G) 8 gyurcsek.istvan@mik.pte.hu

Symmetric Receivers Housing Parasitic capacitances

Shielding Symmetric grounded Common in, output, house

input terminals and GND Symmetric GND-indept.

9 Symmetric Receivers Housing Parasitic capacitances input Z in U out output input U out output Z in Z in Shielding Symmetric grounded Common in, output, house GND Same impedances bw. input terminals and GND Symmetric GND-indept., protective shielded Output, house on GND Same parasitic impedances bw. input terminals and shield asymmetrization Guard is on one input terminal (asymmetric GND-indept. receiver) 9 gyurcsek.istvan@mik.pte.hu

10 Signal Source (TX) Models Signal Receiver (RX) Models TX-RX Interconnections Noisy Signals, Noise Reduction Grounding, Earthing Solutions

Rules for Interconnections 1 RULES OF THUMB System can be grounded at single point! system must be grounded at single point! Build symmetric circuit - if it is possible.

11 Rules for Interconnections 1 RULES OF THUMB System can be grounded at single point! system must be grounded at single point! Build symmetric circuit - if it is possible. (for better noise suppression) Fix the shield potential! Connect the shield of test lead to shield of receiver! Connent the cold point (L) of source to GND! target low voltage bw. test lead and shield 11 gyurcsek.istvan@mik.pte.hu

12 Rules for Interconnections 2 THERE IS NO WAY ( something is incompatible! ) 12 gyurcsek.istvan@mik.pte.hu

13 Interconnection Example 1 Lead shielding Z in U out output ASYMMETRIC GND-INDEPT. ASYMMETRIC GROUNDED System ground 13 gyurcsek.istvan@mik.pte.hu

14 Interconnection Example 2 Lead shielding output Z in U out Z in ASYMMETRIC GND-INDEPT. SYMMETRIC GROUNDED System ground 14 gyurcsek.istvan@mik.pte.hu

15 Interconnection Example 3 Lead shielding output Z in U out Z in SYMMETRIC GND-INDEPT. SYMMETRIC GROUNDED System ground 15 gyurcsek.istvan@mik.pte.hu

16 Interconnection Example 4 ASYMMETRIC GROUNDED Lead shielding Shielding Z in U out output PE PROTECTIVE EARTH ASYMMETRIC GND-INDEPT., SHIELDED System ground 16 gyurcsek.istvan@mik.pte.hu

ASYMMETRIC GROUNDED SYMMETRIC System ground

17 Interconnection Example 5 Lead shielding Shielding Parasitic capacitances U out output Z in PE ASYMMETRIC GROUNDED SYMMETRIC System ground GND-INDEPT., SHIELDED 17 gyurcsek.istvan@mik.pte.hu

18 Interconnection Example 6 Lead shielding Shielding U out output PE ASYMMETRIC GROUNDED SYMMETRIC System ground GND-INDEPT., SHIELDED 18 gyurcsek.istvan@mik.pte.hu

19 SUMMARY

20 Rules for Lead Shielding GND-indept. Source Lead shield to GND at receiver Grounded source w/o offset Lead shield to GND at source Grounded source w. GND-offset Lead shield to GND-offset at source GND-indept. RX (shielded 1 / shielded 2) Lead shield to RX shield 1 / shield 2 Lead shield to GND at source ONLY Ground loop!!! 20 gyurcsek.istvan@mik.pte.hu

21 Signal Source (TX) Models Signal Receiver (RX) Models TX-RX Interconnections Noisy Signals, Noise Reduction Grounding, Earthing Solutions

22 Noisy Signals Effect of noise [SIGNAL] + [NOISE] = [DISTORTION] (info loss!) Distorted signal resultant of signal and noise L SNR (db) = 20 log U S U N Noise SRC Noise always comes into measuring system by means of coupling! Signal SRC Coupling Noise Transmission Channel Signal Distorted Signal Receiver 22 gyurcsek.istvan@mik.pte.hu

23 Couplings Coupling types Conductive galvanic connection Inductive coupling by magnetic induction Capacitive electrostatic coupling Acoustic mech. vibration, audio noise

filtering - (signal post-processing) Using different signal frequency than noise frequency (rule of thumb!

24 Noise Reduction Methods Eliminating the noise source (reducing its impact) Eliminating coupling (reduce its impact) Filtering noisy signal on receiver side Analog filtering (analog filter integrated in RX) Digital filtering - (signal post-processing) Using different signal frequency than noise frequency (rule of thumb!) Active Noise Reduction Etc!!! Noise Source Resulting Noise Anti Noise 24 gyurcsek.istvan@mik.pte.hu

Classification of Electric Noise According to time varying behavior DC Noise time invarian (magnitude) AC Noise time variant (freq, magnitude, phase) Transient Noise short signal! (ie.

25 Classification of Electric Noise According to time varying behavior DC Noise time invarian (magnitude) AC Noise time variant (freq, magnitude, phase) Transient Noise short signal! (ie. Switch on/off an inductive load) Stochastic noise continuous spectrum, broadband According to appearance in measuring circuits Differential Mode Noise (DMN) Common Mode Noise (CMN) DMN caused by CMN

The DMN and CMN Differential Mode Noise (DMN) [DMN, ][series

input terminals are controlled in counter phase Common Mode Noise

are controlled in common phase SOURCE RECEIVER Z IN U DMN U S U S

26 The DMN and CMN Differential Mode Noise (DMN) [DMN, ][series noise], [transversal noise] Series noise in measuring loop RX input terminals are controlled in counter phase Common Mode Noise (CMN) [CMN] Noise of source with offset-gnd RX input terminals are controlled in common phase SOURCE RECEIVER Z IN U DMN U S U S SOURCE RECEIVER U CMN System GND 26 gyurcsek.istvan@mik.pte.hu

If Z RX Z IN + r U DMN U CMN Parameter Common Mode Rejection (CMR) PE U CMN System

27 DMN Caused by CMN [CMN] [DMN] Double GND CMN in measuring loop creates DMN SOURCE wire resistances RECEIVER U DMN = Z RX Z RX + Z IN + r U CMN Z IN US U S +U DMN Z RX If Z RX Z IN + r U DMN U CMN Parameter Common Mode Rejection (CMR) PE U CMN System GND CMR (db) = 20 log U CMN U DMN, (asymm. ~0dB) 27 gyurcsek.istvan@mik.pte.hu

Common Mode Rejection of Symmetric Input SOURCE RECEIVER Z IN

11 = Z 22 = Z, ΔZ = Z 2 Z 1 Z Common mode input impedance ΔZ

1 Z ωc 22 = 1 11 ωc 22 U DMN U CMN = ΔZ Z CMR (db) = 20 log U

28 Common Mode Rejection of Symmetric Input SOURCE RECEIVER Z IN US U S + Z RX U DMN U DMN U CMN U CMN System GND System GND Z 11 = Z 22 = Z, ΔZ = Z 2 Z 1 Z Common mode input impedance ΔZ impedance of wire asymmetry Z 1 = Z IN + r 1, Z 2 = r 2 Z 11 = 1 Z ωc 22 = 1 11 ωc 22 U DMN U CMN = ΔZ Z CMR (db) = 20 log U CMN U DMN = 20 log Z ΔZ 28 gyurcsek.istvan@mik.pte.hu

29 Ways to Increase CMR Eliminate double grounding! CMR (db) = 20 log U CMN U DMN = 20 log Z ΔZ Symmetric realization, ΔZ=0 High common mode input impedance (Z) (low parasitic capacitance) Protective shielding (Guard) (lower resultant capacitance) Shielding Housing 29 gyurcsek.istvan@mik.pte.hu

Noise Sources Contact potential (local galvan cell min.# contacts + corrosion protection) Thermal potential (contact of diff. metals, temp dept. DMN min.

30 Noise Sources Contact potential (local galvan cell min.# contacts + corrosion protection) Thermal potential (contact of diff. metals, temp dept. DMN min.# contacts) Transmission resistance (unsafe contacts in switches clean contacts) Electromagnetic disturbances (channel in external EMF twisted pair, proper GND, magnetic shielding) Electric disturbances (due to parasitic capacitances, possible DMN or CMN separate noise source and channel a/o GROUNDED electrostatic shielding) Switch ON/OFF disturbances (transient noise w. conductive, capacitive, inductive coupling (at opening L or short circuiting C ) overvoltage protection, current limitation Cable bending disturbances (piezoelectric effect in insulation bw. cable and shield compliance w. bend requirements) Power line origin disturbances (parasitic capacitances of main transformer electrostatic shielding bw. primer and seconder winding (row of chopper, grounded) 30 gyurcsek.istvan@mik.pte.hu

31 Signal Source (TX) Models Signal Receiver (RX) Models TX-RX Interconnections Noisy Signals, Noise Reduction Grounding, Earthing Solutions

32 What is Ground? Ground (GND) = voltage reference point, voltage of 0V (electronics, electrical engineering) Comment Not all voltage measurements are in reference to ground. Why connecting to Earth? Earth potential (at certain point!) = almost constant (high capacity of Earth!) Symbol for Earth Ground AND Common Ground (confusing!) 32 gyurcsek.istvan@mik.pte.hu

Earth Ground Earth Ground Physically (and

rod, physically driven into the earth to min.

33 Earth Ground Earth Ground Physically (and electrically) connected to earth (copper, aluminum, aluminum alloy) NEC definition (National Electrical Code) Conductive pipe / rod, physically driven into the earth to min. depth of 8 feet (~2.5 m). 33 gyurcsek.istvan@mik.pte.hu

34 Ground Types Protective Earth (PE) Grounded conductor connected to the normally non-voltage metal parts of electrical equipment Life protection function! Forbidden to use in normal operation! Common Ground (power ground) Common point of power supply (operation current!) Analog Signal Ground (A-GND) Reference point for analog signal system Digital Signal Ground (D-GND) Reference point for digital signal system System Ground (S-GND) SINGLE common point of other grounds, connected to Earth potential Rule of thumb to avoid noisy ground... Separate "more-noisy" digital return currents from "less-noisy" analog return currents. Use single grounding point = "star" ground (difficult to implement!) or grounded bus bar 34 gyurcsek.istvan@mik.pte.hu

Neutral, Earth and Ground Wires in Power System (https://en.wikipedia.

35 Neutral, Earth and Ground Wires in Power System ( Neutral Return path for AC circuit carries current in normal condition Neutral wire is always assumed to be charged Neutral wire is to ground (by grounding) to make it at zero potential No difference between Earthing and Grounding but... Grounding North American standards (IEEE, NEC, ANSI and UL etc) Earthing European countries, Britain standards (like IS and IEC etc) Earth or Ground For safety against leakage or residual currents via least resistance path May be connected to body of equipment In case insulation failure supposed to carry (some minor) current

36 Grounding Symbols General ground or earth ground (IEEE Std section and IEC ). Low-noise ground (IEEE Std section and IEC ) Safety or protective ground (IEEE Std section and IEC ). Chassis or frame connection (IEEE Std section and IEC ). Common connections/potential level not specified (IEEE Std section )

37 Grounding Examples 1 Series grounding WRONG MAIN SYSTEM GROUND RIGHT! Star (radial) grounding RIGHT MAIN SYSTEM GROUND 37 gyurcsek.istvan@mik.pte.hu

38 Grounding Examples 2 Photo from Róbert Czékus student, 2018 Photo by Áron Papp student, gyurcsek.istvan@mik.pte.hu

39 Ground Loop Double grounding ground loop CMN and DMN disturbances SOLUTION: galvanic insulation in loop (grounded source and grounded receiver can be connected no DMN caused by CMN due to different ground potentials) NOT ALWAYS EASY!

40 Insulation Method 1 Flying Capacitor Z IN U S Z RX PE U CMN System GND System GND Capacitor = analog memory High CMR in case of low parasitic capacitances! 40 gyurcsek.istvan@mik.pte.hu

41 Insulation Method 2 Isolation Transformer 41 gyurcsek.istvan@mik.pte.hu

Insulation Method 3 Optoisolator Suggested

load... 100mA Insulation voltage 1000-2500 V

At analog transmission linearity error (low

42 Insulation Method 3 Optoisolator Suggested solution for analog signals Features Max. load mA Insulation voltage V Coupling capacitance < 1 pf. At analog transmission linearity error (low dynamic range) Insulation Phototransistor Photodiode SOURCE RECEIVER Insulation Darlington circuit Insulation 42 gyurcsek.istvan@mik.pte.hu

43 Questions

Sensors DR. GYURCSEK ISTVÁN

Sensors DR. GYURCSEK ISTVÁN DR. GYURCSEK ISTVÁN Sensors 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)