TDC1011_15 Datasheet, PDF (39/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

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TDC1011
SNAS662 – JULY 2015
The measurement process is identical to the level example above. The speed of sound can be used to uniquely
identify a variety of fluids. In this example, the concentration of diesel exhaust fluid (DEF) is measured with a
desired accuracy resolution of 0.5% of concentration variation. For most fluids, the speed of sound varies over
temperature, so every application will be different. In this example, all samples were all at ambient temperature of
23°C.
9.2.1.3 Application Curves
The data used in the following level and fluid identification graphs was collected using an ultrasonic test cell. The
test cell is an acrylic plastic container with width of 2.54 cm and ultrasonic transducers attached to the outside
using cyanoacrylate glue. The transducers in this experiment were STEMiNC 1MHz piezo electric ceramic discs
(SMD10T2R111). Equivalent transducers with the following characteristics could be used:
• Piezo material: SM111
• Dimensions: 10mm diameter x 2mm thickness
• Resonant frequency: 1050 kHz (thickness mode)
150
135
120
105
90
75
60
45
30
2
3
4
Fluid Height in Tank
Full (10 cm)
Full – 1 (9 cm)
Full – 2 (8 cm)
3 cm
2 cm
5
6
7
8
9 10
Height (cm)
Time-of-Flight (µs)
145
131
118
50
35
Figure 53. Time-of-Flight for Fluid Height in Tank
1650
1625
1600
1575
1550
1525
1500
1475
1450
1425
1400
Fluid
Distilled water
Tap water
DEF 10.0%
DEF 20.0%
DEF 30.0%
DEF 31.5%
DEF 32.0%
DEF 32.5%
Speed of sound (m/s)
1481.87
1483.13
1530.49
1576.42
1620.00
1627.37
1629.15
1630.00
Figure 54. Speed of Sound for Various Fluids and Diesel
Exhaust Fluid (DEF) Concentration
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