TDC1011_15 Datasheet, PDF (37/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

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Typical Applications (continued)
9.2.1.1 Design Requirements
Fluid Level
Fluid Identification
DESIGN PARAMETER
Range
Accuracy
Distance
TDC1011
SNAS662 – JULY 2015
Table 14. Design Parameters
EXAMPLE VALUE
2 – 10 cm
0.5% concentration variation
5.08 cm
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Level Measurements
For level sensing applications, the total time-of-flight (TOF) of the sound wave in the fluid is measured. The
pulses transmitted by a bottom mounted transducer travel through the fluid, to the surface of the fluid. The
discontinuity between the fluid and air generates a reflected wave which returns back to the bottom mounted
transducer.
At the beginning of a measurement cycle, the transducer is connected to a transmit channel of the AFE, and the
transmit burst excites the transducer to generate an ultrasound wave. Synchronous to the TX burst, a START
pulse is generated by the TDC1011 to indicate the start of a measurement. After the transmission is completed,
and depending on the device configuration, the transducer is connected to a receive channel of the AFE.
When a valid echo is received, the TDC1011 generates a STOP pulse. Generation of multiple STOP pulses is
possible through register configuration of the device. The START and STOP signal times are compared to
determine the TOF.
The level of the fluid can be determined using the following equation:
61( × ?
@=
2
where
• d is the fluid level in meters (m)
• TOF is the time-of-flight in seconds (s)
• c is the speed of sound in the fluid in meters per second (m/s)
(6)
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