U niversal T ransducer I nterface

1. Universal Transducer Interface

2. Universal Transducer Interface Technical aspects and examples

3. Universal Transducer Interface A single chip digitiser for Resistive sensors Capacitive sensors

4. Universal Transducer Interface The one chip digitiser Configuration of output signal Excitation for resistive sensors Selfcalibrating by three signal technique Measuring capacitive sensors without parasitics

5. Vcc Output configuration: - one line - CS/PD line - Vcc 2.9 - 5.5 V(max 3 mA. Icc). E A B C D F Out Toff Tbc Tcd Toff PD/CS Gnd Time frame of output signal (10/100 ms) Universal Transducer Interface

6. Resistivemode E A B C D F Excitation: - counter-phase - ± 5 kHz Vcc Universal Transducer Interface

7. Resistivemode E A B C D F Vcc Vx Gnd Vcc Universal Transducer Interface

8. Resistivemode V Vx Gnd V/T UTI = - Voltmeter -V/T converter Out Universal Transducer Interface

9. Resistivemode Output Signal ------------------- E A B C D F V Toff Tab Tbc Offsetmeasurement V/T Toff=A*Voff Toff: two periods for synchronisation Out Universal Transducer Interface

10. Resistivemode Output Signal ------------------- E A B C D F V Toff Tab Tbc V/T Tab=A*(Vab+Voff) Out Universal Transducer Interface

11. Resistivemode Output Signal ------------------- E A B C D F V Toff Tab Tbc V/T Tbc=A*(Vbc+Voff) Out Universal Transducer Interface

12. Resistivemode Output Signal ------------------- E A B C D F V Toff Tab Tbc V/T Etc. Tcd=A*(Vcd+Voff) Complete output time frame is about 100 ms (or 10 ms by selection) Out Universal Transducer Interface

13. Resume Calculation inMicrocomputer Tcd-Toff A*(Vcd+Voff)-A*Voff ------------= ---------------------------- Tbc-Toff A*(Vbc+Voff)-A*Voff Vcd Vde = ----- and also ------ Vbc Vbc Toff= A*Voff Tbc=A*(Vbc+Toff) Tcd=A*(Vcd+Voff) Tde=A*(Vde+Voff) Universal Transducer Interface Resistivemode A direct relation between Vcd and Vbc without offset Called thethree signal technique

14. Universal Transducer Interface Resistivemode three signal technique WHY? Nooffset errors Nogain errors Notemperature drift No long term drift

15. Universal Transducer Interface Resistivemode IN PRACTICE THIS MEANS high accuracy (15/16 bits) no offset and gain adjustment cost effective solution

16. Resistivemode E A B C D F Example Rbias Rref Toff Tab Tcd Toff=A*Voff Tab=A*(Vab+Voff) Tcd=A*(Vcd+Voff) Tcd-Toff Vcd i*R(Pt100) Pt100 M=----------- = ------ = --------------- = ------- Tab-Toff Vab i*Rref Rref Pt100 Pt100 measurement Universal Transducer Interface

17. Example E A C D B F Toff Tab Tcd Vcd*32 M = --------- Vab A direct releation between the bridge imbalance and the excitation Voltage Bridge measurement Universal Transducer Interface Resistivemode

18. All kind of resistive elements Universal Transducer Interface Resistivemode

19. Universal Transducer Interface A real revolution in Sensor Interfacing digitises not only resistive elements but also all kind of capacitive sensors

20. Universal Transducer Interface The next slide tells you how the UTI scores!

21. a little theory two pole measurement Cp Coax cable Cx ParasiteCp parallel to Cx Measurement is disturbed by cable capacitance not preferable Universal Transducer Interface Capacitivemode

22. a little theory four pole measurement Cx Cp Cp i V I and V are shortcuts for capacitances so no influence of parasitics preferred solution inside the UTI of course Universal Transducer Interface Capacitivemode

23. A = current input B / F = voltage output A B C D E F i Cab Tad Tab Tac Tab=A*(Cab+Coff) Coff=internal capacitance Tab = two periods for synchronisation Universal Transducer Interface Capacitivemode

24. output signal ------------------- A B C D E F i Cac Tad Tab Tac Tac=A*(Cac+Coff) All not-used outputs on Gnd. (see four pole measurement) Universal Transducer Interface Capacitivemode

25. output signal ------------------- A B C D E F i Tad Tab Tac Cad Tad=A*(Cad+Coff) All not-used outputs on Gnd. (see four pole measurement) Universal Transducer Interface Capacitivemode

26. output signal ------------------- A B C D E F i Tad Tab Tac Cp has no influence due to four pole measurement All not-used outputs on Gnd. (see four pole measurement) Universal Transducer Interface Capacitivemode

27. resume calculation in Microcomputer Tac-Tab A*(Cac+Coff)-A*(Coff) ----------- = ------------------------------ = Tae-Tab A*(Cae+Coff)-A*(Coff) Tab=A*(Cab+Coff) Tac=A*(Cac+Coff) Tad=A*(Cad+Coff) Tae=A*(Cae+Coff) Cac Cad ----- and similar ------ Cae Cae Cab is the lowest for synchronisation (left open in practice) When Cae is reference Cac and Cad are calculated as fraction of Cae(=Cref) Tab=A*(Coff) Universal Transducer Interface Capacitivemode Again the three signal technique to measure the direct relation between a Cx and Cref

28. Angle/Tilt sensor A B C D E F some calculation C1 C2 ---- and ---- Cae Cae If C1/C2 needed then Cae and Caf not critical C1 C2 Cae Caf Cba left open for sync and offset Universal Transducer Interface Example Capacitivemode

29. Pressure sensor A B C D E F Cba left open for sync and offset Cea and Cfa reference capacitor Universal Transducer Interface Example Capacitivemode

30. Exotic application for three capacitors up to 300 pF B C D A E F + Universal Transducer Interface Example Capacitivemode

31. Multiple capacitors measurment setup MUX D B C A E F Especially designed for level gauging purposes accuracy over 4 meter better than 0.1 mm Etc. MUX Universal Transducer Interface Example Capacitivemode

32. Block diagram SEL 1-4 for mode selection Available in PDIP and SOIC version Universal Transducer Interface

33. Thank you for your attention Ask for a demonstration tel +31 76 520 53 53 SmartecNL@compuserve.com