Problems with orifice plate flow transmitters
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There is a Screwmont differential pressure flow transmitter on site, of the orifice plate type; the gauge range is 0.10 kPa, while the range specified by the process DCS is 0–3200 nm3/h. The current reading is above this range. The process team says that the amount of gas being used now is higher than before. The transmitter can be adjusted to a maximum of 65 kPa using a 475 setting, but how should it be adjusted to obtain an accurate differential pressure value, and to what extent?
It’s not just a problem with the transmitter; the size of the orifice in the orifice plate also plays a role. It is recommended not to make arbitrary changes – replacing the orifice plate is the proper solution
The differential pressure and flow rate values for orifice plates are calculated by the manufacturer based on parameters provided by the user; these values cannot be changed by the user themselves. It is necessary to have the manufacturer recalculate them before a new orifice plate can be manufactured.
Oh, then the process modification range is 5000 nm3/h – how large should the transmitter’s range be adjusted?
Oh, thank you. Can it be greatly improved using 475?
This post was last edited by 659zhulinfeng on 2019-9-22 at 21:58. The ratio of the differential pressure range equals the square of the ratio of the flow rate range; for a pressure of 65 KPA, the corresponding flow rate is 0.1/65, which is equal to (3200/m) * (3200/m). You can determine the corresponding differential pressure value based on the desired flow rate for your process. For example, if you need the flow rate to be increased to 5000, then 0.1/p equals (3200/5000) * (3200/5000), where p represents the resulting differential pressure value. However, only minor adjustments are possible; too large changes will result in excessive errors. This is the most commonly used formula in instrumentation: the square root of the differential pressure ratio equals the ratio of flow rates, or the differential pressure ratio equals the square of the ratio of flow rates
One article I published was titled \"A set of test questions on basic knowledge of instruments, created by myself.\" 》 You can download and take a look at them – some common calculation problems needed for daily work with instruments
Then show it to me, thank you
There is a relationship between flow rate and differential pressure: Q = ΔP^(1/2)； Let: the flow rates before and after modification be: Q1, Q2 ； The differential pressure is ΔP1. From the equations Q1 = ΔP1^(1/2) and Q2 = ΔP2^(1/2), it follows that Q1/Q2 = (ΔP1/ΔP2)^(1/2). Among the four quantities Q1, Q2, ΔP1, and ΔP2, two are known and one is specified; by using these, it is possible to determine the value of the remaining quantity. The premise of this method is that the Reynolds number of the medium remains essentially unchanged after the flow rate changes. Otherwise, the orifice plate should be recalculated.
Find the A4 sheet that came with the instrument packaging box, along with the calculation sheet; check what the maximum flow rate for the orifice plate is and what the maximum flow rate it can handle. Then recalculate the pressure difference – there should be no problem