TDC1011_15 Datasheet, PDF (38/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

TDC1011
SNAS662 – JULY 2015
www.ti.com
Trigger
START
TX
Echo Pulse
received
RX
TOF
STOP
Figure 52. Relation Between Transmit and Receive Pulses in Level Measurements
Level measurements have 2 main criteria: resolution and range (maximum height). Resolution accuracies of 1-2
mm are achievable but are impractical due to any environmental disturbances, such as tank vibrations, creating
millimeter level surface waves. Ranges of up to 1 m are measurable utilizing VDD level excitation pulses, but
surface disturbances and signal loss over longer distances make the reliable echo reception an issue. Greater
level measurement reception can be achieved by mechanical means (level guide tube) and/or electronic means
(level shifting the TX pulses to greater voltages; see TIDA-00322).
9.2.1.2.2 Fluid Identification
The TDC1011 can be used to measure the time-of-flight for a known distance to calculate the speed of sound
(c_medium) in the fluid. This application utilizes the same circuitry as the level example but a transducer in a side
mounted configuration transmitting across the container or to a target at a known distance from the transducer.
The temperature can also be measured to compensate for the temperature variation of sound. With the known
distance, TOF and temperature, the speed of sound in the fluid can be determined and the identity of the
medium verified.
After measuring the time-of-flight for the fixed distance, the speed of sound can be calculated as follows:
2×@
?_IA@EQI = ₆₁₍
where
• c_medium is the speed of sound in the fluid in meters per second (m/s)
• d is the level in meters (m)
• TOF is the time of flight in seconds (s)
(7)
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