Seeking help with orifice plate flow rate issues
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Today I encountered an issue related to flow rate measurement using a orifice plate. The original design specified a maximum flow rate of 50 t/h for this orifice plate, but the operator believes that the actual flow rate should be 60 t/h based on process requirements. However, the actual value displayed was 40 t/h. The range of the orifice plate is 0–160 kPa; at that time, the reading was 90 kPa with a current of 12 mA. If the actual flow rate truly is 60 t/h, then why is the differential pressure only 90 kPa, rather than the maximum value? Why isn’t the output current 20 mA?
This situation is due to changes in the operating conditions: the flow rate increases while the pressure difference decreases, which results in a lower range setting. As a result, even though the flow volume is high, the pressure drop is low, so the displayed flow value is low.
The main parameters of orifice plate flow meters include the maximum flow rate, minimum flow rate, and typical flow rate. You mentioned that the maximum flow rate is 50 t/h, but the operators believe that, from a process perspective, the flow rate should be 60 t/h. This indicates that the operating conditions under which the orifice plate is used have changed significantly, and it is no longer suitable for the current process. Additionally, the operator believes that 60 t/h is based solely on intuition and may not be accurate.
This post was last edited by zhaohh3211 on 2013-5-17 at 12:52. The basis for stating 60 T/h is unclear; I think it’s necessary to check the zero point. If the flow measurement range is too small, it can be increased appropriately. However, there is no linear relationship between differential pressure and flow – rather, there is a linear relationship between the square of the differential pressure and flow. For more details, relevant information can be consulted!
The orifice plate is installed there and has not been replaced; the calculated range is 160 kPa. At a differential pressure of 90 kPa, the flow rate should be 3/4 of the maximum flow rate. 50 * 3/4 = 37.5 m3/h. The process indicates that the flow rate should be around 60 t/h, but the instrument shows around 40 t/h. Solutions: 1. Use another measurement method for verification, such as an ultrasonic flow meter. 2. Calibrate the differential pressure flow meter unit to check for any changes in the orifice plate measurements, and verify that the zero and range settings of the differential pressure transmitter are correct. There’s still no problem; check with the manufacturer to see if the calculation sheet is correct.