Originally posted on February 3, 2020 @ 11:41 pm
A flow meter is a tool or a device utilized to measure and gauge volumetric or mass, nonlinear, or linear flow rate of a gas or a liquid. When it comes to selecting flow meters, you must consider such elusive factors as spare parts availability, the familiarity of plant personnel, the average time between failure history, and their practical knowledge with calibration and maintenance, and many more, at the specific plant site.
Furthermore, it is recommended and suggested that the market price of the installation be calculated and determined only after taking these courses of action. One of the generally known flow measurement mishaps is the opposite of these steps. Rather than choosing a sensor which will function correctly, an endeavor is crafted to rationalize the use of a tool because it’s less expensive.
Keep in mind that those cheap purchases can be, for the most part, the most expensive installations. For a little help, here is everything you need to know about flow meters so that you can better understand their functions.
The foundation of right flow meter preference is, for the most part, a plain and direct understanding of the essentials of the specific application. Moreover, time must, more often than not, be invested fully to evaluate the essence of the process fluid and the entire installation.
Okay, so, the first step to choose the right flow meter is to know if the flow rate info must be totalized or continuous and if this information is needed remotely or locally. If the information is required remotely, should be the transferral be shared, digital, or analog? If shared, what’s the minimum or required data update frequency?
If you answered all of these questions, an assessment of the flow characteristics and properties of the piping, and of the process fluid that’ll shelter the flow meter, must take place. For you to achieve this step in an orderly manner, there are forms developed for you to fill in.
Flow and Fluid Characteristics
The fluid and its density, allowable pressure drop, temperature, pressure, viscosity, conductivity, and vapor pressure at optimum operating temp are listed, along with a manifestation of how these characteristics may interact or vary. Additionally, all toxicity and safety information must be given, along with the detailed data on the composition of the fluid, presence of solids, bubbles, light transmission qualities, and tendency to coat.
Temperature and Pressure Ranges
Expected maximum and minimum temperature and pressure values must be provided along with the regular operating assessment when choosing flow meters. Whether flow can go backward, whether slug flow can occur, whether it doesn’t always make the pipe full, or whether specific warnings are required during maintenance and cleaning, these things, too, must be stated.
Installation and Piping Area
With regards to the area and piping where the flow meters are, for the most part, to be situated, consider the regulators, valves, downstream or upstream turns, accessibility, flange-pressure rating, schedule, material, size, direction, and available pipe, specifically straight pipes, run lengths.
The designated engineer should know if magnetic or vibration fields are possible or present in the area. Or if pneumatic or electric power is available, if the place is susceptible for an explosion, or if there are other requirements like sanitary regulations.
Accuracy and Flow Rates
So, the next step in the process is determining the needed meter range by knowing the maximum and minimum flows that’ll be gauged. Then, the required flow measurement accuracy is identified.
Normally, accuracy is stated in the rate of the actual reading, in the rate of the calibrated span, or the rate of the full-scale units. The required accuracy must be stated separately at maximum, normal, and minimum flow rates.
If you do not know these requirements, then the performance of your flow meter might not be acceptable or allowable over its optimum range. In instances where products are purchased or sold on the grounds of a meter reading, complete accuracy is crucial. In other cases, repeatability might be more critical than perfect accuracy. Thus, it’s recommended to create the repeatability and accuracy requirements separately.
If the accuracy of a flow meter is in % calibrated span or % full-scale units, its error will shoot up as the flow rate decreases. On the other hand, if the absolute error is in % actual reading, the error remains the same at low or high flows.
Since FS is a massive quantity compared to the CS, a sensor in the rate of the full-scale units will always have a considerable error compared to the % CS specification. Thus, for you to compare these things fairly, it is recommended to convert all errors into the same % actual reading units.
Repeatability vs. Accuracy
If allowable metering representation can be, for the most part, taken from two distinct flow meter categories and one of them has immovable parts, choose the one with immovable parts. Keep in mind that moving parts are a, believe it or not, a potential source of various issues — for example, sensitivity to coating, lubrication, and clearance spaces.
Even if you maintain it well, the temperature and fluid viscosity changes. And these changes need compensation. Moreover, if you can get the same performance from both a point sensor and a full flow meter, it’s recommended to use the flow meter.
Types of Flow Meter
Actually, there are plenty of flow meters available in the market, like the Smart Measurement Flow meter, today. Here are some of them:
- Variable Area or Rotameters. It is a float and a tapered tube and used for liquids, and gases flow measurement because it is affordable, low-pressure drop, simplicity, and wide range ability.
- Mass Gas. This type of flow meter operates with minimal density, fluid viscosity, and pressure. It uses a temperature sensor and a differential pressure to identify the true mass flow rate.
- Pitot Tubes. Pitot tubes offer low-cost, easy installation, low maintenance, lower pressure loss, and good resistance to wear. It requires sizing though.
- Vortex Meters. The primary advantages of this type of flow meter are their minor sensitivity to changes in process conditions, and low wear relative to turbine meters. In addition, initial and maintenance expenses are low.
Numerous factors are influencing the life expectancy and maintenance requirements of flow meters. The main factor is pairing the correct instrument to the right application. Poorly chosen devices will only lead to problems. And for sure, you do not want any of that. Essentially, all flow meter requires some type of maintenance.