Ultrasonic transit-time flow meter

volumefor gasDN25 - 1"

Short description YUNYI Gas Ultrasonic Flowmeter is a non-contact instrument that uses ultrasonic technology to measure gas flow in pipelines. Its measurement control module handles ultrasonic signal transmission/reception, calculation, display control and communication. The module connects to ultrasonic transducers, pressure sensors, temperature sensors and a display, and can be powered by an internal lithium battery or external DC supply. Flow measurement results can be output via pulse signals, analog output (4–20 mA), RS-485 (Modbus RTU) and other interfaces.

Key Features

• Time-difference correlation (transit-time) principle for flow calculation
• Accuracy classes: 0.5 and 1.0
• Fits pipe sizes from DN25 to DN300
• Supports single, dual, four and six-channel configurations with channel fusion algorithm
• Low-noise signal processing with automatic temperature drift and zero drift compensation
• High-precision temperature and pressure acquisition and standard volume correction
• Turndown ratio > 1:160 with segmented meter factor settings
• Large on-board data storage: 5,000+ historical records, 1,000 start/stop records, 100 alarm records and 20 months of cumulative totals
• Gas composition and compressibility factor calculation (AGA8-92DC or SGERG-88)
• Meets GB/T 18604-2014 and JJG 1030-2007 standards
• Intelligent transducer fault detection
• Power: supports internal lithium battery or external DC supply

Working Principle The module uses the transit-time difference method: ultrasonic waves travel faster downstream and slower upstream. Flow velocity V is calculated from upstream and downstream transit times. Volumetric flow q is obtained by q = V × S, where S is the pipe cross-sectional area. A cross-correlation algorithm transforms signals to the frequency domain to ensure high noise immunity and stability.

Standard Volume Correction Flow under working conditions is converted to standard conditions (e.g. 101.328 kPa absolute, 0°C or 20°C) using the real gas equation and compressibility factor calculations (AGA8-92DC or SGERG-88). The instrument supports conversion between working and standard volumetric flows using measured temperature, pressure and calculated compressibility factors.

Output Signals (summary table) Type — Details
Calibration pulse — 3-wire, opto-isolated, external 12–24 V DC, range ≤50 m. Configurable for working or standard flow.
IC card pulse — 2-wire, CMOS 3.3 V, low level idle. Pulse width 5–500 ms, pulse equivalent 0.01–10 m³. Internal power, range ≤5 m. Optional open-drain module.
Alarm outputs — CMOS 3.3 V, active high. Three alarms: battery low (<3.5 V), battery critical (<3.1 V), flow rate over limit (configurable).
RS-485 — Modbus RTU, half-duplex, configurable baud rate, electrically isolated. Data includes temperature, pressure, flow (working/standard), accumulations, battery, alarms, fault codes, compressibility factors and system configuration.
4–20 mA — 2-wire, isolated, 24 V DC, range ≤200 m. Maps to working or standard flow (user configurable); 4 mA = lower limit, 20 mA = upper limit.

Data Storage

• Last 5,000 records: timestamp, temperature, pressure, working/standard flow & accumulations (logging interval 1–60 min)
• Last 1,000 start/stop events
• Last 100 alarms (flow over limit, sensor fault, etc.)
• Last 20 months of working and standard accumulations

Environmental & Operating Conditions

• Ambient temperature: –20°C to +60°C
• Relative humidity: 5% to 95%
• Atmospheric pressure: 50–110 kPa
• Medium temperature: –20°C to +60°C
• Medium must be free of oil and impurities; flow and pressure must be within specified ranges

Display & Operation Totalizer range: 0–9,999,999,999 Nm³ (standard) or m³ (working). Flow rate display: 0–±999,999 Nm³/h or m³/h. Temperature display: –99.9 to 99.99 °C. Pressure display: 0–9,999 kPa. Battery icon: 0–3 bars. External power icon and backlight supported. Flow direction indicator and sensor fault indication (-ER- flashing). Keys: BP1 (next page / save), BP2 (cursor shift / digit selection), BP3 (increment digit), BP4 (confirm / exit).

Modbus RTU Communication Protocol: Modbus RTU (master-slave). Parameters: 1 start bit, 8 data bits, 1 stop bit, no parity (configurable). Baud rates: 2400, 4800, 9600, 19200 (default 19200). Slave address: 1–247 (default 1). Function code: 0x04 (read input registers). Data format: big-endian, floating-point (single precision) or 64-bit unsigned integer for accumulations (scaled by 1000). Example registers: 0x0000 working flow (m³/h); 0x0002 standard flow (Nm³/h); 0x0004 working accumulation (positive); 0x000C temperature (°C); 0x000E pressure (kPa); 0x0010 battery (%). Diagnostic registers provide transit times, time difference, sound velocity, gas velocity, gain and SNR for each channel.

Notes The instrument supports dedicated ultrasonic transducers (supplied), I²C digital temperature sensors (specified model) and I²C absolute pressure sensors (specified model).