Various Features of Liquid Flow Meters

Liquid flow meters are used for measuring the flow rate of liquids as the name suggests. Flow meters have become an essential device for numerous industries. From food and beverages industries to oil and gas plants, chemical and different pharmaceutical factories have wide range applications of flow meters to measure gas, liquid or both. Current progress in technology especially related to innovation in flow sensing devices has led to more durable, reliable, accurate and cost-effective meters. That said, the characteristic that is most important following today’s industrial demand is having flow meters that are computer-interfaced. So it can be monitored instantaneously and remotely to giving out the flow measurements. 

Features

Due to the increasing industrial demands, new and updated flow meters are announced integrated with advanced features. Though there are various types of flow meters available, the general features for considering a flow meter are the same. Accuracy in measurements, flow velocity range, installation method and maintenance requirements are some features of the flow meters that should be considered while selecting the appropriate flow meter. Moreover, features like output connectivity options and mechanical restrictions should also be considered. In addition to that, fluid characteristics like viscosity, single or double phase, temperature, pressure, conductivity, turbidity, corrosiveness and flow profile like transitional, turbulent or laminar also significantly influence the performance of the flow meters. Hence, considering these features leads to the correct application of the technology and metering device.

Below are the list and details of some of the key features of the flow meters that are important to be considered before their application.

·         Flow Range:

The flow velocity range of the flow meter is determined by the minimum and maximum volumetric or mass flows; the flow meter is capable of measuring. This ability of the flow meter is obtained by taking the ratio of maximum to minimum flow rates. Moreover, it is also obtained through a Reynolds Number. This ability of the flow meter is commonly denoted as turndown ratio. Using the meter outside its linear range can affect its performance

·         Repeatability:

The repeatability of the flow meter is based on two techniques.

                    i.            Metering: The repeatability of a particular flow meter, through metering, is tested when the results of the successive measurements, using that particular meter are approximate, in conditions where the same quantity was measured by the same procedure, by the same person at the same location over a short duration. More precisely, it is the feature of the meter to give approximately close values under certain and constant conditions.  

                  ii.            Laboratory Technique: In laboratory test technique the repeatability of the meter is checked through comparing the difference obtained in successive measurements under some definite conditions, by the same operative using the same device plus same material and test technique.

·         Accuracy:

The accuracy of the flow meter is termed as its skill to determine the nearest approximation of the true value. Once if the precise measurements and characteristics of the fluid and pipes to be used are noted down then the next step is to find appropriate flow meter with high accuracy rate. Percentage of calibrated span (CS), the percentage of actual reading (AR), or percentage of full scale (FS) units are typically used to specify the accuracy of the flow meters. The indication of meter accuracy as % CS and % FS signifies that with the decrease of measured flow rate the absolute error will increase. Whereas % AR signifies no change in absolute error with the fall and rise in flow rates.

·         K-Factor:

The ratio of number pulses of the meter to the corresponding net volume of the fluid flowing through the meter at the time of measurement is known as K factor of the meter. To put in simple terms it is the pulses per unit volume. It is an electronic indication of volumetric output.  The received pulses are continuously divided by the k factor through the electronic device giving various outputs like rate and factor totalization. 1\k is usually termed as meter factor. Though the frequency of the pulses is directly proportional to the turbine rotor rotational rate the effects like thermal and change in pressure can alternate the K factor of the meter. So the manufacturer of the meter should be consulted if the K factor varies with changes in liquid form or with changes in the area of the pipe.

·         Linearity:

 The dependability of the K factor over a particular flow rate is defined as the Linearity of the flow meter.  This linearity of the flow meter is usually defined as the band, containing minimum and maximum K factors and also K  mean.  The manufacturer usually specifies these lower and upper limits as the maximum and minimum flow range of the particular liquid or other constraints in meter manufacturing such as temperature and pressure.