Regarding changes to the flow range
Thread Content
Our plant currently has an orifice plate used for measuring flow rate via a differential pressure transmitter; the flow rate range for this orifice plate is 0–14,000 Nm/H, with the corresponding differential pressure range being 0–10 KPA. Now we need to set the flow rate range to 0–18,000 Nm/H. What should the differential pressure range be in this case?
If high precision is not required, change the range to 16.5 KPA; if high precision is needed, it’s best to have the manufacturer do the calculations
The differential pressure after the range change is calculated using software. You can also ask the manufacturer to do the calculation
The flow rate is proportional to the square root of the pressure difference; by using this relationship, a formula can be formulated to carry out the calculation
(14/18)X(14/18)=10/required differential pressure
Our factory has also encountered this situation, and we adjusted the range of the variation by performing calculations. It is understandable to just change the range of the variation; but can the range of the orifice plate be changed arbitrarily?
As mentioned above, this changes the range of the differential pressure; so how is your differential pressure range determined? Isn’t it still based on the range of the orifice plate?
This problem isn’t difficult to solve; it’s just a bit troublesome. The normal calculation steps for an orifice plate are: to calculate the orifice plate based on the flow rate at full scale and other parameters. The calculation results provide several possible outcomes (“orifice diameter – differential pressure – pressure loss”). Select one suitable orifice plate and the range of the differential pressure transmitter. For the situation you mentioned of \"changing the flow rate value at full scale,\" there are two solutions: [Solution 1] Replace the orifice plate. If replacing the orifice plate, simply follow the aforementioned steps for calculating and selecting an orifice plate. The orifice plate was remanufactured. Modify the transmitter range (the range ratio of standard transmitters can generally cover this). The disadvantage of this solution is its high cost (price of the new orifice plate + installation costs). The advantage is that it meets the process requirements in terms of pressure loss. 【Option 2】Use an old orifice plate and specify the orifice diameter during calculation. The differential pressure value corresponding to the new flow rate at that aperture is determined. Then modify the transmitter range. The advantage of this solution is cost savings. The downside is that the pressure loss is fixed (not adjustable), and it increases (high pressure loss means higher operating costs for the device). If comprehensive costs are taken into account, one cannot consider only the cost of the instruments! ! ! !
The square root of the pressure difference ratio equals the flow rate ratio. The differential pressure range is changed to 16.5 KPA
The flow rate is proportional to the square root of the pressure difference; by using this relationship, an equation can be formulated to carry out the calculation. The answer provided on floor 9 was excellent