SNAS648C October   2014  – February 2023 TDC1000

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information (1)
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Transmitter Signal Path
      2. 8.3.2 Receiver Signal Path
      3. 8.3.3 Low Noise Amplifier (LNA)
      4. 8.3.4 Programmable Gain Amplifier (PGA)
      5. 8.3.5 Receiver Filters
      6. 8.3.6 Comparators for STOP Pulse Generation
        1. 8.3.6.1 Threshold Detector and DAC
        2. 8.3.6.2 Zero-Cross Detect Comparator
        3. 8.3.6.3 Event Manager
      7. 8.3.7 Common-Mode Buffer (VCOM)
      8. 8.3.8 Temperature Sensor
        1. 8.3.8.1 Temperature Measurement With Multiple RTDs
        2. 8.3.8.2 Temperature Measurement With a Single RTD
    4. 8.4 Device Functional Modes
      1. 8.4.1 Time-of-Flight Measurement Mode
        1. 8.4.1.1 Mode 0
        2. 8.4.1.2 Mode 1
        3. 8.4.1.3 Mode 2
      2. 8.4.2 State Machine
      3. 8.4.3 TRANSMIT Operation
        1. 8.4.3.1 Transmission Pulse Count
        2. 8.4.3.2 TX 180° Pulse Shift
        3. 8.4.3.3 Transmitter Damping
      4. 8.4.4 RECEIVE Operation
        1. 8.4.4.1 Single Echo Receive Mode
        2. 8.4.4.2 Multiple Echo Receive Mode
      5. 8.4.5 Timing
        1. 8.4.5.1 Timing Control and Frequency Scaling (CLKIN)
        2. 8.4.5.2 TX/RX Measurement Sequencing and Timing
      6. 8.4.6 Time-of-Flight (TOF) Control
        1. 8.4.6.1 Short TOF Measurement
        2. 8.4.6.2 Standard TOF Measurement
        3. 8.4.6.3 Standard TOF Measurement With Power Blanking
        4. 8.4.6.4 Common-Mode Reference Settling Time
        5. 8.4.6.5 TOF Measurement Interval
      7. 8.4.7 Averaging and Channel Selection
      8. 8.4.8 Error Reporting
    5. 8.5 Programming
      1. 8.5.1 Serial Peripheral Interface (SPI)
        1. 8.5.1.1 Chip Select Bar (CSB)
        2. 8.5.1.2 Serial Clock (SCLK)
        3. 8.5.1.3 Serial Data Input (SDI)
        4. 8.5.1.4 Serial Data Output (SDO)
    6. 8.6 Register Maps
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Level and Fluid Identification Measurements
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Level Measurements
          2. 9.2.1.2.2 Fluid Identification
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Water Flow Metering
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Regulations and Accuracy
          2. 9.2.2.2.2 Transit-Time in Ultrasonic Flow Meters
          3. 9.2.2.2.3 ΔTOF Accuracy Requirement Calculation
          4. 9.2.2.2.4 Operation
        3. 9.2.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information
9.2.2.2.2 Transit-Time in Ultrasonic Flow Meters

Transit-time ultrasonic flow meters works based on the principle that sound waves in a moving fluid travel faster in the direction of flow (downstream), and slower in the opposite direction of flow (upstream).

The system requires at least two transducers. The first transducer operates as a transmitter during the upstream cycle and as a receiver during the downstream cycle, and the second transducer operates as a receiver during the upstream cycle and as a transmitter during the downstream cycle. An ultrasonic flow meter operates by alternating transmit and receive cycles between the pair of transducers and accurately measuring the time-of-flight both directions.

GUID-7210CFB3-5982-4627-AAF2-877FA66B43A7-low.gifFigure 9-8 Relation Between Transmit and Receive Pulses Upstream/Downstream

In this example, the upstream TOF is defined as:

Equation 8. GUID-17360007-D673-4ED4-9460-34B55747FD45-low.gif

where

  • l is the path length between the two transducers in meters (m)
  • c is the speed of sound in water in meters per second (m/s)
  • v is the velocity of the water in the pipe in meters per second (m/s)

In this example, the downstream TOF is defined as:

Equation 9. GUID-950D31FE-DA03-4307-8F9C-ED7A01AE908E-low.gif

where

  • l is the path length between the two transducers in meters (m)
  • c is the speed of sound in water in meters per second (m/s)
  • v is the velocity of the water in the pipe in meters per second (m/s)

The difference of TOF is defined as:

Equation 10. GUID-A3CAF25D-2660-4CC3-A5B6-167981308909-low.gif

where

  • tBA is the upstream TOF from transducer B to transducer A in seconds (s)
  • tAB is the downstream TOF from transducer A to transducer B in seconds (s)

After the difference in time-of-flight (ΔTOF) is calculated, the water velocity inside the pipe can be related to the ΔTOF using the following equation:

Equation 11. GUID-974C4EAF-8A58-47D7-933E-CEAC5B565982-low.gif

where

  • c is the speed of sound in water in meters per second (m/s)
  • l is the path length between the two transducers in meters (m)

Finally, the mass flow rate can be calculated as follows:

Equation 12. GUID-3449686F-54FA-414C-BE9A-5B31EE677AC2-low.gif

where

  • k is the flow meter constant
  • v is the velocity of the water in the pipe in meters per second (m/s)
  • A is the cross-section area of the pipe in meters-squared (m2)