TDC7200_15 Datasheet, PDF (38/50 Pages) Texas Instruments – TDC7200 Time-to-Digital Converter for Time-of-Flight Applications in LIDAR,Magnetostrictive and Flow Meters

TDC7200
SNAS647C – FEBRUARY 2015 – REVISED AUGUST 2015
www.ti.com
3 = :0.015 I³/D; l ^{1 D} p = 4.167T10^F6 I³/O
3600 O
2. Calculate the flow velocity assuming k = 1:
3 4.167T10^.6 I³/O
R= =
G#
è (^{0.0125 I})²
= 0.0236 I/O
3. Calculate the ΔTOF for the given speed of sound. In this example, a speed of sound c = 1400 m/s is
assumed:
2 × H × R (2)(0.06 I)(0.0236 I/O)
¿61( = _?2 =
1400 I/O²
= 1.445 JO
4. The requirement of 5% accuracy for minimum flow will result in a ΔTOF accuracy of:
¿61(_ANNKN = :0.05;:1.445 JO; = 72.25 LO
For this reason, this system requires a high accuracy timer/stopwatch that can measure the lower flow rate state.
The TDC1000 ultrasonic analog-front-end is used to drive the transmitter, amplify and filter the received
signal and conditioning the echo for START and STOP pulse generation. The TDC7200 ps-accurate timer is
used to measure the time interval between the rising edge of the START pulse and the rising edge of the
STOP pulse produced by the TDC1000.
The microcontroller should first configure the TDC7200 and the TDC1000 for the measurement. When the
microcontroller issues a start command to the TDC7200 via the SPI interface, the TDC7200 sends a trigger
pulse to the TRIGGER pin of the TDC1000. When the TDC1000 drives the transmit transducer, a
synchronous START pulse is produced on the START pin, which commands the TDC7200 to start its
counters. When a valid echo pulse is received on the receive transducer, the TDC1000 generates a STOP
pulse on the STOP pin, which commands the TDC7200 to stop its counters. This procedure is repeated for
the upstream and downstream cycles.
A temperature measurement can be performed and the result can be used to correct for temperature
dependency of the speed of sound.
9.2.3 Application Curves
Figure 46 , Figure 47, and Figure 48 show data and histograms created with data collected under a zero flow
condition at room temperature. A simple offset calibration has been applied, where the overall average of the
data is subtracted from the data.
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
Raw calibrated data
10x running average
1000
2000
3000
Samples (n)
4000
5000
Figure 46. Calibrated Raw and Averaged Delta Time-of-Flight Data
6000
38
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