What is “Instantaneous Flow”?
It is commonly known that a flow rate type of flowmeter measures the moving speed of certain instantaneous fluid. This so-called "Instantaneous Flow Volume” is to assume that the fluid has been running at the same speed for a period of time (for example, LPM is one minute) measuring how much volume of a fluid will pass through. The instantaneous flow volume can also be said to be a portion of a certain time period of the cumulative flow. During this period, the instantaneous flow volume can be high or low, and after some period of time, the flow data at each instance only represents the fluid state at that moment. Meanwhile, the cumulative flow is the result of the accumulation of data for countless instantaneous flows. The data of the two are related but not necessarily the same. For example: In a flow monitoring period of one minute, the instantaneous flow volume measured in one millisecond is 60 LPM, and the instantaneous flow volume in another millisecond is 40 LPM, but the cumulative flow measured after one minute is 50 LPM.
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Relationship between “Instantaneous Flow” and “Cumulative Flow”.
Cumulative = sum of all instantaneous flows measured over a period of time ÷ the total time.
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How do users obtain “Instantaneous Flow” data?
Manual recording, human visual real-time monitoring.
The field personnel monitors and records the data on the flowmeter at a fixed time. However, this method is only suitable if the flowmeter is installed near the field personnel’s operation place so he does not need to travel frequently when monitoring the flow. To add, this way of data monitoring does not require external equipment or a central control system for the work area.
Although this method is known to have relative promptness and reliability, but, due to factors such as cost,size, and design of the screen that varies within the different flowmeters in the market, the effectiveness is not guaranteed. For example, if the flowmeter is installed in a location where it’s difficult to monitor at a close distance or under conditions such as dim lighting of the area, it will make the visual monitoring extremely challenging. This gives the field personnel the difficulties that can be prone to errors.
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Transmission of data by electronic signal
In relatively large and advanced work areas, all equipment data is coordinated and recorded by PLC (Programmable Logic Controller). Generally, individual devices and PLCs are connected by wired communication by means of signal transmission such as RS485, 4-20mA, or switch signals. This method will have special requirements on the wired communication equipment of individual devices. The above three items are explained as follows：
Switch Signals | The upper and lower limit alarms can be set to monitor the instantaneous flow volume. If pulse is used, the instantaneous flow volume can be obtained after calculation.
To confirm if the instantaneous flow volume is in a normal state, it can be obtained through the logic that “data is greater than the upper limit corresponding to the analog current output” and if the logic is “data is less than the lower limit corresponding to the analog current output” built into the flowmeter or in the central control system alarm setting function, then the data cannot be obtained. For example: if the user wants to set the instantaneous flow volume of a liquid on the production line to 60 l/s. In order to control the injection speed and injection volume of the liquid, he can set the upper limit to 62 l/s and lower limit to 61 l/s in the upper and lower limit functions, and an alarm will be generated if it exceeds or is insufficient. In addition, it also assists to confirm whether the liquid flow is at a normal value, and properly controls the amount and speed of liquid injection. Some mechanical flowmeters, such as variable area flowmeters equipped with a magnetic pointer or a magnetic ring, can transmit switching signals by setting the upper and lower limits to confirm the current flow monitoring status. In addition, this method can also use the transmission throughout the pulse signal, and then obtain it by recording the time of the PLC and calculating the instantaneous flow volume. The disadvantage is that it requires more PLC time and the accuracy is poor at low flow.
4-20mA｜A single dedicated line that receives instantaneous flow volume, provides the fastest, most reliable and smallest delay of data suitable for automatic control.
If the user permits to use a single dedicated line to transmit data, and the data needs to be reliable and immediate, 4-20mA will be the most suitable type of data transmission. For example, when the user is engaged in automatic control, sometimes it is necessary to ensure that the delay requirement is still within a thousand fraction of a second or even lower, making 4-20mA very suitable for data transmission. However, because the principle is within the current range of 4-20mA, the data will change accordingly according to the flow rate and the preset range, so the correct setting of the corresponding flow range of 4-20mA is the premise of the correctness of the data. But still, the range has its limit, so when it reaches 20mA, it needs to be reset manually to start collecting data again, so there are fewer users using this method. Even so, this method can still be used as a feedback for the accumulated flow.
RS485｜The transmission line is one-to-many, and the delay time for data collection is long, but the data is the most diversified and can be transmitted over long distances.
The RS485 transmission line is a one-to-many connection. If the user does not have immediate needs, RS485 can directly collect various data on the cumulative flowmeter for subsequent applications, which is suitable for data collection. However, the PLC engineer needs to write another program to decode the communication content according to the manual of different flowmeters.
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Communication Transmission Recommendations
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Switch Signals |
4-20mA |
RS485 |
Paper records |
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Instantaneous Flow
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Upper and lower limits can be set, but relatively less accurate, less real-time, and more computationally intensive. |
🏆
Lower delay for one-to-one dedicated lines.
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Relatively long delay. |
Handwritten record. |
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Cumulative Flow
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🏆
The most common is Pulse, which instantly returns the unit volume.
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Less used.
Available in LORRIC flow meters, but less commonly used on the market.
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The delay is relatively long, and there is a zero-return function.
There is a cumulative flow of dates provided.
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Handwritten record. LORRIC provides a 14-day cumulative flow record.
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Others
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Some Alarms can output via Pulse, but they are limited because it can only select one output (or a large class of output). |
Less used. |
🏆
You can get the most information, self-health, settings, environmental parameters.
One wiring can communicate with multiple units.
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Handwritten record. |
* 🏆 Indicates a more common usage than others.
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Data application of "Instantaneous Flow"?
Try to use "vehicle speed" as an analogy to "Instantaneous Flow". "Vehicle speed" provides the driver's awareness of how fast the current driving speed is. With "vehicle speed" information, the driver can avoid the penalty for violating traffic rules or even possible accidents cause by over over speeding. We can also compare "Instantaneous Flow" to "fire" and "time" during cooking. If it is only for boiling water, the greater the heat, the faster the water can be boiled; however, when it comes to cooking, it is very important to control the fire and the length of time. Some dishes need to be fried quickly in a short time to make the ingredients crispy and fragrant; some dishes need to be simmered slowly to make the ingredients soft and delicious. The two data of "fire" and "time" will be one of the keys to determine whether the dish is delicious or not.
According to the above logic, "Instantaneous Flow" has different interpretations for different industries and applications. For example, in some industries, factories need to take into account the different reaction times of chemicals, and need to perform more complex and detailed control. If two or three chemicals need to be injected at the same time, the monitoring of the instantaneous flow is very important. We can say that when users care about various details in the "process", then the data of "Instantaneous Flow" is very important to them.
In addition, in LORRIC's point of view, whether it is "Instantaneous Flow" or “Cumulative Flow", both are the basic data that the flowmeter can provide, and it is also the so-called environmental data. Any application or process that needs to consider environmental factors, the data of "Instantaneous Flow" will play a very important role.
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