Generally, velocity-type flow meters measure the fluid's movement speed at any given moment. 'Instantaneous flow rate,' also known as momentary flow, assumes that the fluid maintains the same speed over a period (like LPM, which is per minute) to determine the volume of fluid that passes through. It's a snapshot of the cumulative flow over a time slice, where the instantaneous flow can vary within a period, and over time, each momentary flow data point only reflects the fluid's state at that instant. In contrast, cumulative flow is the result of countless instantaneous flows accumulated, and while the data of the two are related, they may not be identical. For example, in a one-minute flow monitoring period, the instantaneous flow may be 60 LPM at one millisecond and 40 LPM at another, but the cumulative flow measured after one minute could be 50 LPM.
Manual recording, real-time monitoring by visual inspection.
On-site personnel monitor and record at the flow meter's location at set times and frequencies. This method is suitable if the flow meter is installed near the operation site, requiring no frequent back-and-forth movement. Also, this data recording method doesn't require additional equipment or a central control system. Although relatively immediate and reliable, this method poses difficulties in visually monitoring if the flow meter is installed out of easy sight or in dimly lit conditions.
In larger and more advanced operation fields, all device data, such as PLC (Programmable Logic Controller), are coordinated and recorded, typically connected via RS485, 4-20mA, or switch signals for wired communication. Specific requirements apply to the wired communication setup of individual devices. The above three methods are explained as follows:
Switch Signal | Can set upper and lower limits for alerts to monitor instantaneous flow. If using a pulse, it requires calculation to obtain the instantaneous flow.
Flow meters with built-in or central control system alarm settings for "data above the analog output current upper limit" and "data below the analog output current lower limit" can indicate whether the 'Instantaneous Flow Rate' is normal, but data is not obtained. For example, to control the injection speed and volume of a certain medicine, users can set the upper limit to 62/lower to 61, with alerts for over or under to ensure proper control. Mechanical flow meters, like those equipped with magnetic pointers or magnetic rings, can send switch signals based on these limits to confirm the current flow monitoring status. Additionally, this method can use pulse signals transmitted by volume, which the PLC records over time and calculates to obtain instantaneous flow. However, this requires more PLC time and is less accurate at low flows.
4-20mA | A single dedicated line receives instantaneous flow, providing the most reliable and fastest data with minimal delay, suitable for automatic control.
If users can transmit data on a single dedicated line and need reliability and immediacy, 4-20mA is the most suitable data transmission type. However, the correct setting of the corresponding flow range for 4-20mA is a prerequisite for data accuracy. The range has its limits, so at 20mA, manual resetting is required to start collecting data again, making this method less commonly used. Nevertheless, it serves as feedback for cumulative flow.
RS485 | Multi-device transmission lines, longer data collection delays, but the most diverse data, suitable for long-distance transmission.
RS485 allows multi-device connections, and if there's no need for immediacy, it can directly collect various data from cumulative flow meters for subsequent applications, suitable for data collection. However, PLC engineers need to write additional programs to decode the communication based on different flow meter manuals.
Application of 'Instantaneous Flow Rate' Data?
We liken 'Instantaneous Flow Rate' to 'vehicle speed,' which provides the driver with an awareness of the current driving speed. By monitoring 'vehicle speed,' drivers can avoid speeding tickets and potential accidents. Similarly, 'Instantaneous Flow Rate' can be compared to the 'heat' and 'time' in cooking. If the goal is simply to boil water, the higher the heat, the faster it boils. However, for cooking, the control over the intensity of heat and duration is crucial. Some dishes require a quick stir-fry over high heat for crispiness and aroma, while others need to be simmered slowly for softness and flavor. These two data points, 'heat' and 'time,' are key to the deliciousness of a dish.
With this logic, 'Instantaneous Flow Rate' has different interpretations across various industries and applications. For example, some industries sometimes need to consider individual chemical reaction times, requiring complex and delicate control. Monitoring instantaneous flow becomes critical when injecting two or three chemicals simultaneously. In short, when users care about the details 'during the process,' the data on 'Instantaneous Flow Rate' is very important to them.
Furthermore, from LORRIC's perspective, both 'Instantaneous Flow Rate' and 'Cumulative Flow' are basic data provided by flow meters, also known as environmental data. Any application or process that needs to consider environmental factors will find 'Instantaneous Flow Rate' data very important.