How to calibrate the gas flow meter displayed by DCS

Actual flow rate = (4*323/5*373)^0.5*60000 = 49939 (Nm3/hr; the unit depends on your specifications), and it is inversely proportional to pressure and temperature in a square root relationship

This post was last edited by HEJIYUER on 2015-7-22 at 19:49. It is a simple method for estimation; no modifications are required, nor is temperature or pressure compensation needed. 1. Design condition A: full scale of 60,000 cubic meters, operating density of 3 KG/M3. (The flow rate unit can be KG or NM3, but it must have no relation to the operating density. If it is M3, convert it to KG; it doesn’t matter if the value isn’t an integer). Well, you now have a flow scale of 60,000 cubic meters, for an operating density of 3 KG/M3; it is called the “A flow scale”. 2. Actual operating condition B, operating density 2 KG/M3. Let’s calculate a \"B-flow scale\" for an operation density of 2 KG/M3; its full scale value is: SQRT(2/3)x60000 = 48990 cubic units. Practical application method: If the DCS flow rate is 30,000, it corresponds to the \"A flow scale\"; first calculate the percentage of the full range: 3/6 = 0.5. 4. Converted to the “B flow scale,” 48990x(0.5) = 24495 cubic units, which represents the actual flow rate at an operation density of 2 KG/M3. Therefore, you must provide the \"scale flow rate\" at full scale for conversion; merely providing the flow rate at the operating point is not sufficient for \"back calculation\", as there is no \"B flow scale\". @jiaguoyun

This kind of conversion is often encountered when new units are put into operation: there is a significant deviation between the operating pressure of the gas and the design conditions (a deviation in density). However, the process requires knowing the actual value of this flow rate to facilitate operational comparison. Since it is temporary, there is no need to modify the differential pressure range of the transmitter. For SIS orifice plate transmitters, since it is not convenient to modify/download them online, this approach can also be used. So, to calculate the scale values of scale B, this method can be used to estimate the actual flow rate; it’s a riddle-like question. Sarcastic remark: Look at the ——A scale in the bowl, and think about the ——B scale in the pot. The device is stable; if this pressure still fluctuates due to process-related issues, then pressure compensation can be applied. The DCS configuration is simple, and the process temperature does not change much, so it may not be necessary to carry out compensation calculations. However, the temperature of the meter still needs to be taken into account. Design density and operating density can be provided by the process. If regular gases have a molecular weight, it can be roughly calculated using temperature and pressure formulas; it’s still just an estimate of the flow rate. @jiaguoyun