When selecting the ideal flow meter for your industrial application, there are certain aspects you need to pay attention to. Accuracy and repeatability are two of them. They are main key factors to look at when picking an ideal flow meter for your flow meter system. In this article, we will be discussing the importance of repeatability and accuracy in flow meters. This information is quite vital when you are deciding which flow meter to install in your flow system.
What is Accuracy in Flow Measurement?
Advancement in technology and innovation has largely contributed to high accuracy measurement in flow meters. This means that flow meters are now providing more accurate readings, making them more efficient and reliable than before. But what exactly do we mean when we say that a flow meter is accurate?
The closeness between the true value and given flow measurement is what determines accuracy. When it comes to flow meters, accuracy is based on the difference between the calibration curve of the flow meter and its output. Readings are given as percentages, and a flow meter will be deemed more accurate if the readings are lower.
When working with flow meters, you need to understand that not all applications or flow meter systems will require accuracy. For example, if you measure simple concepts such as determining the quantity of liquid or gas that flows into the pipe, it is okay if the readings will stray away from the calibration curve. However, accuracy is critical when dealing with complex concepts such as mixing volatile elements. Primarily, what determines the cost of a flow meter device is its price.
If you intend to use your flow meter in applications that don’t require more accuracy for applications, there is no need to spend much on expensive flow meters that provide high accuracy readings. To gauge a flow meter’s accuracy, two specification settings are used – full scale and reading.
Full Scale (FS)
Full-scale readings are outdated and are no longer used in many applications nowadays. Initially, they were commonly used with Industrial mechanical gauges. Back then, readings were done by checking the physical marks on the dial. When measuring the closeness to the true value, full-scale specification is used. The full-scale reading is expressed as a percentage of the closeness to the true value against the full-scale value. You will need to multiply the gauge’s full-scale pressure by the accuracy percentage if you want to determine accuracy as a full-scale percentage. Although this method is not specific when measuring fluids, it is much easier to calculate and interpret. They have to be much closer to the barometric pressure to give higher accuracy since flow sensors don’t perform consistently while in full range.
Most flow meter devices that work digitally use reading due to the specification of the precise measurement. This type of setting determines flow accuracy as the true value’s percentage. This is given by multiplying the pressure of the reading by the percentage of the accuracy. When the pressure lowers, the pressure becomes better. Floor specifications accompany these types of readings. Uncertainties such as measurement noise and resolution are accounted for. Although they produce the same results, these techniques of specification execute their functions uniquely. One system may be more beneficial than the other based on the measured pressure.
Accuracy Building Blocks
There are three critical building blocks that makeup accuracy. These blocks include:
- Calibration and measurement capability (CMC)
Calibration & Measurement Capability
High accuracy levels depend largely on a reliable calibration method and equipment. A value is used to express CMC. It also checks the credibility of a flow rate measuring equipment by gauging how well it can read or measure. The value doesn’t have to be fixed. Most of the time, it is given as a range to account for fluctuations.
CMC’s level of uncertainty is expected, just like any other piece of equipment that is never 100 percent accurate. In varying circumstances, these uncertainties will increase or decrease when the flow pressure is low, for instance. When it is used, any statistical variations and inaccuracies that occur will be accounted for by CMC. Using a flow meter that works well and performs consistently helps to get reliable readings. Another vital component of accuracy comes in when you need to achieve reliable readings – repeatability. To better understand the importance of repeatability, let’s explain it vividly.
The act of the flow meter producing flow accurately from time to time is called repeatability. It can also be defined as giving the same readings all the time without any fluctuations. Using an ideal flow meter, the same flow readings are expected from it when it works under similar conditions and variations. These conditions include fluid properties, flow rate, pressure, temperature, and more. At a specific flow rate, the repeatability of the device is determined by the reading, which allows the flow meter to resume the flow when it falls to zero. The general picture of the readability of the device is given by measuring the discrepancies between subsequent readings and the first reading.
Repeatability gives the same results under the same conditions, in other words, when operating system under the same variables and conditions, the meter should give the same readings.
Getting perfectly similar results is not always possible. There have to be moderate discrepancies in different readings. You can conclude that the device has reliable repeatability conditions if the reading range gives almost the same figures. A flow meter with good repeatability conditions sits reading range may fall within 95, 96, and 98 units per minute. The fluctuation here is quite minimal.
Readings given by an instrument with poor repeatability will widely differ and may seem to follow the minimal reason or rhythm. For example, 50, 77, and 100 units per minute. Such readings show that conditions of repeatability are quite distorted. The fluctuation levels are intense due to dissimilar numbers.
Accuracy largely depends on repeatability. It is unlikely to get high volume accuracy without high repeatability. However, it is possible to get high repeatability without high accuracy. Verifying the accuracy of readings that vary under similar conditions is hard. Repeatability is necessary for most flow meters and combustion control systems since it allows us to establish accuracy.
Therefore These components bring about uncertainty in the flow measurement process; accuracy is determined by calculating their sum. Pressure and temperature coefficients, conversion factors, and long-term stability may also affect the process’s accuracy. Additional factors need to be taken into account to ensure your devices are functioning as expected.
Accuracy and repeatability are of great value when it comes to flow measurement. However, many tend to underrate these two key factors of flow measurement. They should also help you to select the desired flow meter to be used with your application. Knowing the relationship between your device and accuracy is paramount if you choose the correct flow meter. Considering the level of accuracy needed by your application, the overall design of the flow meter, and your budget are also factors that will eventually affect the accuracy and repeatability of the flow meter; however, if you feel like getting the right flow meter research online first to get reputable value for your money.