Download - Universal Transducer Interface. Universal Transducer Interface Technical aspects and examples
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Universal Transducer Interface
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Universal Transducer Interface
Technical aspectsand
examples
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Universal Transducer Interface
A single chip digitiser for
Resistive sensors
Capacitive sensors
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The one chip digitiser
Configuration of output signal
Excitation for resistive sensors
Selfcalibrating by three signal technique
Measuring capacitive sensors without parasitics
Universal Transducer Interface
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E
A
B
C
D
F
Output configuration:- one line
- CS/PD line - Vcc 2.9 - 5.5 V(max 3 mA. Icc).
Gnd
Vcc
PD/CS
Out
Toff Tbc Tcd Toff
Time frame of output signal(10/100 ms)
Universal Transducer Interface
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Resistive modeE
A
B
C
D
F
Excitation:
- counter-phase- ± 5 kHz
Vcc
Universal Transducer Interface
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Universal Transducer Interface
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A
B
C
D
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Vcc
Gnd
Vcc
Vx
Resistive mode
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Universal Transducer Interface
Gnd
VxV
V/T
Out
UTI =
- Voltmeter
-V/T converter
Resistive mode
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Universal Transducer Interface
E
A
B
C
D
F
V
V/T
Out
Toff Tab Tbc
Output Signal-------------------
Toff=A*Voff
Toff: two periods for synchronisation
Offset measurement
Resistive mode
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Universal Transducer Interface
E
A
B
C
D
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V
V/TTab=A*(Vab+Voff)
Toff Tab Tbc
Output Signal-------------------
Out
Resistive mode
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Universal Transducer Interface
E
A
B
C
D
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V
V/TTbc=A*(Vbc+Voff)
Toff Tab Tbc
Output Signal-------------------
Out
Resistive mode
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Universal Transducer Interface
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A
B
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V
V/TEtc.Tcd=A*(Vcd+Voff)
Complete output time frame is about 100 ms (or 10 ms by selection)
Toff Tab Tbc
Output Signal-------------------
Out
Resistive mode
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A direct relation between Vcd and Vbc without offset
Called the three signal technique
Universal Transducer Interface
Resume
Toff= A*Voff
Tbc=A*(Vbc+Toff)
Tcd=A*(Vcd+Voff)
Tde=A*(Vde+Voff)
Calculation in Microcomputer
Tcd-Toff A*(Vcd+Voff)-A*Voff------------= ----------------------------Tbc-Toff A*(Vbc+Voff)-A*Voff
Vcd Vde= ----- and also ------ Vbc Vbc
Resistive mode
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three signal technique
Resistive mode
Universal Transducer Interface
No offset errors
No gain errors
No temperature drift
No long term drift
WHY?
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IN PRACTICE THIS MEANS
Resistive mode
Universal Transducer Interface
high accuracy (15/16 bits)
no offset and gain adjustment
cost effective solution
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E
A
B
C
D
F
Example
Rbias
Rref
Pt100Toff=A*VoffTab=A*(Vab+Voff)Tcd=A*(Vcd+Voff)
Tcd-Toff Vcd i*R(Pt100) Pt100M=----------- = ------ = --------------- = ------- Tab-Toff Vab i*Rref Rref
Pt100 measurement
Toff Tab Tcd
Resistive mode
Universal Transducer Interface
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E
A
C
D
B
F
Example
Vcd*32 M = --------- Vab
Bridge measurement
A direct releation between the bridge imbalance and the excitation Voltage
Toff Tab Tcd
Resistive mode
Universal Transducer Interface
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All kind of resistive elements
Resistive mode
Universal Transducer Interface
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A real revolution in Sensor Interfacing
Universal Transducer Interface
digitises not only resistive elements
but also
all kind of capacitive sensors
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The next slide tells you
how the UTI scores!
Universal Transducer Interface
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Cx
Cp
Parasite Cp parallel to Cx
Coax cable
two pole measurement
Measurement is disturbed by cable capacitance
not preferable
a little theory
Universal Transducer InterfaceCapacitive mode
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CpCp
Cx
i V
I and V are shortcuts for capacitances sono influence of parasitics
preferred solution
inside the UTI of course
a little theory
four pole measurement
Universal Transducer InterfaceCapacitive mode
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A = current inputB / F = voltage output
A
B
C
D
E
F
i
Tab TacTad
Tab=A*(Cab+Coff)
Tab = two periods for synchronisation
Coff=internal capacitance
Cab
Universal Transducer InterfaceCapacitive mode
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A
B
C
D
E
F
i
Tac=A*(Cac+Coff)
output signal-------------------
All not-used outputs on Gnd.(see four pole measurement)
Cac
Tab TacTad
Universal Transducer InterfaceCapacitive mode
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A
B
C
D
E
F
i
Tad=A*(Cad+Coff)
All not-used outputs on Gnd.(see four pole measurement)
CadTab Tac
Tad
output signal-------------------
Universal Transducer InterfaceCapacitive mode
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A
B
C
D
E
F
i
All not-used outputs on Gnd.(see four pole measurement)
Cp has no influence dueto four pole measurement
Tab TacTad
output signal-------------------
Universal Transducer InterfaceCapacitive mode
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resume calculation in Microcomputer
Tab=A*(Cab+Coff)Tac=A*(Cac+Coff)Tad=A*(Cad+Coff)Tae=A*(Cae+Coff)
Cab is the lowest forsynchronisation(left open in practice)
Tab=A*(Coff)
Tac-Tab A*(Cac+Coff)-A*(Coff)----------- = ------------------------------ =Tae-Tab A*(Cae+Coff)-A*(Coff)
Cac Cad----- and similar ------Cae Cae
When Cae is reference Cacand Cad are calculated as fraction of Cae(=Cref)
Again the three signal technique to measure thedirect relation between a Cx and Cref
Universal Transducer InterfaceCapacitive mode
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Example
A
B
C
D
E
F
Cae
Caf
C1C2
Angle/Tilt sensor
some calculation
C1 C2---- and ----Cae Cae
If C1/C2 needed then
Cae and Caf not critical
Cba left open for sync and offset
Universal Transducer InterfaceCapacitive mode
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Example
A
B
C
D
E
FCba left open for sync and offsetCea and Cfa reference capacitor
Pressure sensor
Universal Transducer InterfaceCapacitive mode
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Example
B
C
D
A
E
F
+
Exotic application for threecapacitors up to 300 pF
Universal Transducer InterfaceCapacitive mode
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Example
D
B
C
A
E
F
MUX
Etc.
MUX
Multiple capacitors measurment setup
Especially designed for level gauging purposes
accuracy over 4 meter better than 0.1 mm
Universal Transducer InterfaceCapacitive mode
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VSS
VDD
ABCDEF
Logic control circuit
FrequencyDivider
Driver
Voltage toPeriod
Converter
AMP/C-V/
DividerMUX
UTI
SEL1 SEL2 SEL3 SEL4 CML SF PD
OUT
Block diagram
SEL 1-4 for mode selection
Available in PDIP and SOIC version
Universal Transducer Interface