Ultrasonic Flow Meters: Clamp-on versus In-Line for Advanced Flow Measurement

Ultrasonic flow meters from Titan Enterprises represent a significant advancement in flow measurement technology, offering precision, versatility, and ease of use without any moving or internal components. These flow meters provide improved electronic processing, enhanced diagnostics, and excellent accuracy. They operate using ultrasound to measure the velocity of a fluid flowing through a pipe of known dimensions, which in turn gives the volumetric flow rate. There are two main types of ultrasonic flow meters: Transit-Time or 'time of flight' ultrasonic flow meters, which measure the time difference between ultrasonic pulses sent in the direction of the flow and against the flow, with the difference in transit time being directly proportional to the flow velocity, and Doppler ultrasonic flow meters, which measure the frequency shift of an ultrasonic signal reflected by particles or bubbles in the fluid, using this shift to calculate flow velocity.

Ultrasonic flow meters can either be integrated into a pipe to measure the flow 'in-line' or clamped onto the outside of an existing pipe. Both in-line and clamp-on flow meters are commonly used for measuring the flow rate of liquids and gases in various applications, each with its advantages and disadvantages, making them suitable for different industrial uses.

In-line flow meters are generally more accurate because they are directly inserted into the pipeline, often measuring over the entire cross-section of the pipe using multiple sensor sets to produce highly accurate data for precise flow rate measurement. These devices can be finely calibrated by the supplier or an independent calibration house to specific standards, which are directly relatable to the final installation. In-line flow meters are available in various measurement technologies, including turbine, magnetic, vortex, or differential pressure, and ultrasonic technology offers the added benefit of minimal or no flow restriction. In-line flow meters tend to provide stable and consistent performance over time, making them reliable for long-term use. They are suitable for both liquid and gas flow measurements and can handle high pressures and temperatures, depending on the construction material and design. However, installing an in-line flow meter typically requires cutting the pipe and sometimes halting the process to empty the pipe prior to installation, which can be time-consuming and costly. Maintenance can also be challenging, as it may require shutting down the process and disassembling parts of the pipeline. Once installed, in-line flow meters are not easily relocated, making them less flexible if measurement points need to be changed frequently. Despite the higher installation costs, in-line flow meters offer low lifetime costs due to their electronic nature and minimal maintenance requirements. They are often used in industries requiring high accuracy, such as oil and gas, where the high accuracy and low maintenance costs quickly offset the initial installation expense.

Clamp-on flow meters, on the other hand, are installed externally on the existing pipe, eliminating the need to cut or alter the pipeline or drain the liquid. This makes them ideal for applications where the process cannot be interrupted. They are easy to install and maintain, as they do not require stopping the flow or cutting into the pipe. Clamp-on flow meters can also be installed in difficult locations or tight spaces, although there may be accuracy implications if not properly placed. These flow meters can be fitted to a variety of pipe sizes, including large diameters, and can be used for a range of fluids. They are also portable, allowing flexibility for temporary installations or spot-check measurements. Because there is no need to alter the pipeline, the installation costs are typically lower than those of in-line flow meters. However, clamp-on flow meters generally have lower accuracy compared to in-line models, as the actual dimension of the pipe wall thickness and bore are important factors in calculating flow measurement accuracy. Factors such as pipe material, wall thickness, internal surface deposits, and flow profile can also impact the accuracy. Calibration is only possible on a representative piped system rather than on the final installed device, which may compromise accuracy. Clamp-on flow meters may not be suitable for very small or very large pipes and can be less effective for certain fluids, particularly those with low velocity or high aeration. Additionally, the condition and material of the pipe can significantly affect the performance of clamp-on flow meters, as pipes with heavy insulation or thick walls may cause signal degradation. Signal interference from nearby electronic equipment or the pipe material itself can also affect measurement reliability. The location of the clamp-on device is also crucial; the device must be installed in a location that minimizes turbulence, which can be ensured by placing the device at least 10 pipe diameters upstream and 5 pipe diameters downstream from bends and valves.

In conclusion, the choice between ultrasonic in-line and clamp-on flow meters depends on the specific needs of the application, such as required accuracy, ease of installation, maintenance considerations, and the nature of the fluid and pipeline. Titan’s range of in-line ultrasonic flow meters utilizes patented 'time-of-flight' ultrasonic technology, offering excellent accuracy over a wide range of liquid flow, from 2 ml/min to 20 l/min.