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
9.2.2.2.1 Regulations and Accuracy

If the flow meter is intended for residential applications, the meter must be designed to meet the required standards. For example, per the INTERNATIONAL ORGANIZATION OF LEGAL METROLOGY (OIML), the metrological requirements of water meters are defined by the values of Q1, Q2, Q3 and Q4, which are described in #GUID-9BBF861B-09AE-4BD2-AE8E-56EDED5297B6/SNAS6484104.

Table 9-3 Flow-Rate Zones per OIML
FLOW RATE ZONEDESCRIPTION
Q1Lowest flow rate at which the meter can operate within the maximum permissible errors.
Q2Flow rate between the permanent flow rate and the minimum flow rate that divides the flow rate range into two zones, the upper flow rate zone and the lower flow rate zone, each characterized by its own maximum permissible errors.
Q3Highest flow rate within the rated operating condition at which the meter can operate within the maximum permissible errors.
Q4Highest flow rate at which the meter can operate for a short period of time within the maximum permissible errors, while maintaining the metrological performance of the meter when the meter is subsequently operating within the rated operating conditions.

A water meter is designated by the numerical value of Q3 in m3/h and the ratio Q3/Q1. The value of Q3 and the ratio of Q3/Q1 are selected from the lists provided in the OIML standards.

Water meters have to be designed and manufactured such that their errors do not exceed the maximum permissible errors (MPE) defined in the standards. For example, in OIML standards, water meters need to be designated as either accuracy class 1 or accuracy class 2, according to the requirements.

For class 1 water meters, the maximum permissible error in the upper flow rate zone (Q2 ≤ Q ≤ Q4) is ±1%, for temperatures from 0.1°C to 30°C, and ±2% for temperatures greater than 30°C. The maximum permissible error for the lower flow-rate zone (Q1 ≤ Q < Q2) is ±3%, regardless of the temperature range.

For class 2 water meters, the maximum permissible error for the upper flow rate zone (Q2 ≤ Q ≤ Q4) is ±2%, for temperatures from 0.1°C to 30°C, and ±3% for temperatures greater than 30°C. The maximum permissible error for the lower flow rate zone (Q1 ≤ Q < Q2) is ±5% regardless of the temperature range.

The flow meter accuracy specified in the standards dictates the required accuracy in the electronics used for driving the ultrasonic transducers, circuits in the receiver path, and time measurement sub circuits. The stringent accuracy required at lower flow rates would require a very low noise signal chain in the transmitter and receiver circuits used in ultrasonic flow meters, as well as the ability to measure picosecond time intervals.