【Instrument Selection】What should you choose for general liquid flow meters?
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【Instrument Selection】For general liquid flowmeters, when it comes to measuring the flow of liquids with low viscosity, most people choose a certain type of flowmeter. In large organizations where high precision is required, mass flowmeters are preferred, while those with lower precision requirements opt for vortex flowmeters. In small units, glass rotameters are generally preferred. Let’s discuss it – which one do everyone prefer? Here is a reference for selecting liquid flow meters: Selection of flow meters. The choice of flow meters plays a very important role in ensuring their successful use. The complexity of the substances being measured, along with the wide variety of flow meters available and their varying performance specifications, make it difficult to select the appropriate meter. There is no perfect flow meter; each type of instrument has its own characteristics. The purpose of selection is to choose the most suitable instrument from among the various options by taking advantage of their strengths and minimizing their weaknesses. Comparison Table of Characteristics for Various Types of Flow MetersType | Item
--- | ---
Orifice | Orifice Plate | Vortex Flow Meter | Vane Flow Meter | Turbine Flow Meter | Annubar Flow Meter | Electromagnetic Flow Meter | Ultrasonic Flow Meter | Mass Flow Meter | Rotameter
Accuracy | 0.5–2.5 | 0.5–1.5 | 0.5–1.5 | High | High | 2.5 | 1.0 | 1.5 | High | 1–2.5
Pressure Drop | Low | High | Moderate | High | High | Low | Low | Low | Low | High | High
Suitability for Low Speeds | Possible | Difficult | Difficult | Possible | Possible | Difficult | Difficult | Difficult | Possible | Possible
Suitability for High Temperatures | Possible | Possible | ---- | ---- | ---- | Possible | ---- | Difficult | ---- | Calibration | Self-check | ---- | ---- | ---- | ---- | ---- | ---- | ----
Handling of Gas Contamination | Possible | ---- | ---- | ---- | ---- | ---- | Possible | Possible
Suitability in Sterile Environments | Possible | Difficult | ---- | ---- | ---- | Possible | Possible | Possible | Possible | ----
Corrosion Resistance | Possible | Difficult | ---- | ---- | ---- | Possible | Possible | Difficult | Possible
Remote Transmission | Possible | Intelligent Type | Intelligent Type | Intelligent Type | ---- | Intelligent Type | Intelligent Type | Intelligent Type | Intelligent Type | ----
Weight | Light | Moderate | Light | Heavy | Moderate | Light | Heavy | Heavy | Heavy | Light
Price | Medium | Medium | Low | Medium | Medium | Low | Expensive | Very Expensive | Low
Suitability for High Viscosity Fluids | Possible | ---- | ---- | Possible | ----
Handling of Conductive Liquids | Difficult | Possible | ----
Suitability for Small Pipe Diameters | Possible | ---- | ---- | Possible | ---- | ---- | Possible | ----
Range Ratio | 5–10:1 | 3:1 | 1:20 | 1:50 | 1:50 | 4:1 | 10:1 | 10:1 | 20:1 | 5:1
Handling of Impurities | Possible | ---- | ---- | ---- | Possible | Possible | ---- | ----
Failure Rate | Low | Low | Low | Moderate | Moderate | High | Low | Low | Low | Low
Types of Media | Gas, Steam, Liquid | Gas, Steam, Liquid | Gas, Liquid | Liquid, Steam | Liquid | Liquid, Steam | Conductive Liquid | Gas, Liquid | Gas, Steam, Liquid | Liquid
Impact of Scaling | Low | High | High | High | High | High | Low | High | High | High
Impact of Adhesion | Low | High | High | High | High | Low | High | Low | High
Measurement Principle | Pressure Difference | Pressure Difference | Frequency | Volume | Volume | Pressure Difference | Velocity | Velocity | Mass Force | Pressure Difference
Compensation Method | Density | Density | Density | ---- | Density | ---- | Density | Density | ----
Accumulation Method | Square Root, Linear | Square Root | Linear | Linear | Linear | Square Root | Square Root | Linear | Square Root | ----
Instant Display | Intelligent Type | Intelligent Type | Intelligent Type | ---- | Intelligent Type | Intelligent Type | Intelligent Type | Intelligent Type | ----
Installation Method | Any | Horizontal | Any | Horizontal | Horizontal | Horizontal | Any | Horizontal | Vertical
Ease of Installation | Easy | Difficult | Easy | Difficult | Difficult | Easy | Difficult | Difficult | Difficult | Easy
Ease of Maintenance and Use | Easy | Requires Specialist | Easy | Easy | Easy | Difficult | Difficult | Easy | Easy
Service Life | Possible | Possible | Moderate | Not Long | Prone to Wear | Not Long | Possible | Possible | Possible | Moderate
The selection of a flow meter can be based on five aspects: instrument performance, fluid properties, installation conditions, environmental conditions, and economic factors. The detailed factors in the five aspects are as follows: 1. Instrument performance aspects such as accuracy, repeatability, linearity, range, flow range, signal output characteristics, response time, pressure loss, etc ； 2. In terms of fluid properties: temperature, pressure, density, viscosity, chemical corrosion, abrasiveness, scaling, multiphase flow, phase transformation, electrical conductivity, sound speed, thermal conductivity, specific heat capacity, isentropic index ； 3. Regarding installation conditions: pipe layout direction, flow direction, length of straight sections upstream and downstream of the sensing element, pipe diameter, maintenance space, power supply, grounding, auxiliary equipment (filters, degasers), installation, etc ； 4. Environmental conditions: ambient temperature, humidity, electromagnetic interference, safety, explosion protection, pipeline vibration, etc ； 5. Economic factors include the cost of purchasing instruments, installation costs, operating expenses, calibration fees, maintenance costs, the service life of the instruments, and spare parts. The steps for selecting instruments are as follows: 1. Initially identify possible types of instruments based on the type of fluid and five consideration factors (several types should be available for selection) ； 2. Collect information on preliminary selection types as well as price data to prepare for in-depth analysis and comparison ； 3. Use the elimination method to gradually narrow down to 1–2 types; repeatedly compare and analyze the five factors to ultimately determine the pre-selected target.
Electromagnetic flowmeters are generally used, rotary flowmeters for pure water, and mass flowmeters for applications with high requirements. Orifice plate flowmeters do not have high accuracy and are only for reference.
Vortex street and electromagnetic methods are both viable, but they also have drawbacks (such as vibration). If the requirements are not high, a differential pressure type can be considered, as it is cheaper; if the requirements are high, then a mass flow meter is the only option
Mass flow meters should be used when precise measurement is required. There are many options available when precision isn’t necessary: differential pressure flow meters, vortex flow meters, electromagnetic flow meters, ultrasonic flow meters, target flow meters, and so on.
A mass flow meter is still the preferred choice; an electromagnetic flow meter can be used if conditions permit, and a rotor flow meter should be chosen last due to its lower cost.
The conductivity of the brine in our plant is quite high; we mainly use electromagnetic flowmeters, but we need to take corrosion into consideration.
We use mass flow meters, rotameters, vortex flow meters, and electromagnetic flow meters quite often
Import brands of ultrasonic and mass flow meters are more reliable, but this also means higher prices, especially for those used with low flow rates. Some domestic brands of other types are relatively good quality at low prices.
The last edit to this post was made by liubo999 on 2009-8-21 at 09:08; for measuring flow rates, mass flow meters are the best choice due to their high accuracy； Orifice plate flowmeters or electromagnetic flowmeters, which are used for general measurement, are cheaper and easier to maintain