Using Flowmeter Diagnostic Data

Using Flowmeter Diagnostic Data
Using Flowmeter Diagnostic Data

Accurate and repeatable measurements are essential to quantify the bulk movement of gas from wellhead to flame tip. In natural gas applications, ultrasonic flowmeters generally offer better performance, greater reliability and lower capital and ownership costs than other flowmeters.

Ultrasonic flowmeters from SICK operate according to the principle of ultrasonic transit time difference measurement. This allows conclusions to be made about the gas volume flowing through based on the sound velocity transfer time. Measurement is carried out in a direct path layout to keep disturbing effects, such as gas flow turbulence, dirt, moisture, or interfering noises, as low as possible. Two ultrasonic transducers are positioned opposite each other in a defined angle to the gas flow and operate alternately as sender and receiver. As a result, ultrasonic flowmeters are more reliable and require less maintenance than mechanical flowmeters.

The development of various meter types has also brought the progression and development of the data that comes along with them. Diagnostic data has come a long way since the introduction of flowmeters decades ago. In this article, we will discuss traditional diagnostic data parameters and some new ultrasonic diagnostic features and enhancements that will improve your flow measurement accuracy, repeatability, and reliability

Traditional diagnostic methods

Five main traditional diagnostic parameters have been around for a long time—since meters were first developed. They are:

Automatic gain control (AGC)
AGC is the amplitude of the received signal that depends on pressure, meter size, and specific damping influence. An increased AGC value indicates a weaker received signal. A weaker signal could indicate that you have contamination in the line. For example, there may be some buildup in front of the transducer or possibly some liquid in the line.

Signal-to-noise ratio (SNR)
SNR is the ratio between the received signal and a noisy signal. It is an indication of the acoustic signal quality. Any time your SNR gets below 30 decibels, you may want to investigate what caused the SNR to drop so low. It is usually an indication of buildup in front of a transducer or noise resonating in the line and interfering with the transmitted signal.

Acceptance rate
The acceptance rate is the ratio between valid measurement signals and the signals being transmitted. It is often indicated in a percentage of how many of the transmitted signals are being received on the other side and indicates the measurement plausibility. For example, if you send out 100 signals between a pair of transducers and are able to receive 100 signals without any rejections, then the acceptance rate is 100 percent. An acceptance rate of 100 percent is often not required. However, the higher your percentage is, the higher your measurement plausibility.

Speed of sound
Speed of sound is an independent measurement value specific to gas composition, pressure, and temperature. It is an indication of the quality of the signal run-time measurement. In general, the speed of sound measured for each path should be within 0.2 percent of one another. If not, it is an indication something is interfering with the signal, or dimensional data has been entered incorrectly.

Flow profile and symmetry
Flow profile and symmetry is a reflection of the flow distribution from the top to the bottom of the pipe. A blocked flow conditioner could cause some issues with accuracy in the meter. This measurement is a quick way of identifying whether or not you have a good profile.

What’s new in ultrasonic diagnostics?

Condition-based indicator (CBI)
The condition-based indicator (CBI) is an additional diagnostic indicator based on a diametrical virtual path. The path is fully integrated into a four-path or an eight-path meter. This helps measure transit time in upstream and downstream applications.

With the next generation of meters, CBI offers the sensor signal transmission in one measurement path. By redesigning the transducers, the sensor can send one signal from measuring path two to measuring path three and from path three to path two. This cross-sectional measurement enables signals to measure the velocity more accurately through the center of the meter in the virtual path. With this, you can set up a tolerance to alarm off the virtual path before the four-path or eight-path meter gives you an alarm, so you can do more comparisons between the two measurements

The dimensionless CBI factor is calculated from the mean gas velocity of the diametrical paths and the mean gas velocity of the four-path meter or eight-path meter with this calculation:

No additional hardware is required for the diametrical measurement and calculation of the CBI. This is due to the latest generation of the ultrasonic sensor with a new sensor head design along with advanced signal processing electronics.

New diagnostics available with commissioning meter installation setup

The Commissioning Meter installation setup within FLOWgate™ software offers new selections on the installation page to identify additional devices upstream and downstream of the ultrasonic meter. Also, you can check any application-specific conditions relevant to the meter. When there is a failure with the meter, you can see warnings associated with the meter and can immediately run through the solutions assistant to help determine what is wrong with the meter.

The new Extended Diagnostics Solution Assistant indicates exactly what diagnoses have failed and tells you proposed actions to solve the problem, which could include pollution, external noise, or a blocked flow conditioner.

The assistant will also archive all diagnostics. The Archive Diagnostics page provides quick access to historical trends of data and events. The chart gives the user a way to analyze data from specific days to monitor activities that occurred during that time period. The archive can also be used in conjunction with the Fingerprint page to create a reference and limit trends. Archive data can be available indefinitely.

New transducer design

Available to technicians out in the field, the latest generation of ultrasonic sensors can determine the CBI value due to the physical propagation of the ultrasonic signal generated by the sensors. The generated signal radiates in the form of a sound beam with a defined angle based on the design of the sensor head. In addition, the sensors, along with new electronics, have up to 12 dB better noise immunity.

The chart shows the testing done to compare the FLOWSIC600-XT to a traditional classic meter. The traditional classic meter failed down to zero, but the XT meter continued to operate and offer flow measurement even under extreme conditions. The new, advanced sensor and the new electronics gave this noise immunity.

PowerIn technology

The highly efficient energy concept of the FLOWSIC600-XT guarantees continuous power via an optional integrated backup battery in the event of a mains power failure. This ensures continuous measuring operation for up to three weeks. The backup battery is a special hermetically sealed battery that can be stored for over 10 years without capacitance loss.

If the external power supply fails, power consumption reduces to the minimum level:
● The standard measuring rate reduces from 10 Hz to 1 Hz.
● The RS485, Ethernet, HART, Encoder interfaces and the analog output are deactivated.
● The frequency and pulse outputs F0.0, F0.1, D0.2, and D0.3 as well as the infrared service interface on the display are available.

Additional enhancements and features

  • Fingerprint enhancement: Capable of creating a diagnostic fingerprint from commissioning data or data recorded at the flow lab during calibration.
  • Extended calibration ranges: Option is available to extend the lower and upper calibration range for better rangeability. Extending the range will optimize operations during seasons of high or low demand nominations. For example, in winter, you may have high demands, and, in summer, you may have low demands. In the past, you had to get two devices to measure the different demand levels. Now, this could possibly be achieved by simply extending the high- and low-end calibration points.
  • Internal pressure and temperature sensor: The integrated pressure and temperature sensor is used for automatic corrections due to geometry and Reynolds effects.

Greater accuracy, repeatability, reliability

New diagnostic data enhancements and features can give you a greater level of accuracy, repeatability, and reliability in your ultrasonic flow measurement applications. In summary, the new features available include:

  • Condition-based indicator: Virtual path measures the velocity through the center of the meter and compares it to the average velocity of the main meter to evaluate meter performance.
  • Enhanced commissioning wizard and solution assistant: In conjunction, the Solution Assistant can help field personnel with evaluating resolutions to errors or warnings that occur in the meter.
  • Archive diagnostics: Quick access page to view events and data logs.
  • New transducer and electronics design: Along with calculating CBI, transducers and new electronics have up to 12 decibels of increased noise immunity.
  • Extended calibration ranges: Extended ranges can provide flexibility when designing a station or meter runs.
  • Integrated pressure and temperature sensor: Provides live pressure and temperature values for corrections related to pipe expansion or Reynolds number effects.
  • Virtual and integration solutions through our service and system integration groups.

This article comes from the January 2021 InTech Focus ebook.

About The Author

Joel Nava is market application engineer–flow metering systems at SICK. He has more than 40 years of experience working with flow measurement technology. Nava applies this expertise to assist with the engineering, R&D, and design of flow metering systems. He has been with SICK, Inc. for over seven years.

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