Issues regarding the use of V-cone differential pressure transmitters for measuring steam flow rates
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The upper limit set for this tag point on the DCS is 36.3 kPa, while the lower limit is 0. The differential pressure range specified in the V-cone calculation sheet is 9.8 kPa. The problem is that after setting this range in the transmitter, the flow rate displayed on the DCS is only in the range of a few dozen tons per hour; this value differs significantly from the steam flow rate indicated by the thermocouple. What I want to know is how to ensure that the measured values are accurate
The V-cone flowmeter is not a standard throttling device and requires calibration with actual flow; otherwise, it is difficult to ensure measurement accuracy. V-cone flowmeters were quite popular over a decade ago, but it seems they have lost popularity in recent years.
It was very popular in the 2000s; I don’t dare to use it now
The differential pressure needs to be squared in order to correspond to the flow rate. This type of flow meter is merely a three-stage detection instrument; it is suitable for process monitoring and control but not for measurement purposes. If measurement is indeed necessary, temperature and pressure compensation measures must be implemented.
The differential pressure needs to be squared before it can be correlated with flow rate. Either take the square root of the differential pressure transmitter value, or take the square root of the DCS value ； Additionally, temperature and pressure compensation is required when measuring steam flow
Then, given the current situation, what range should be set for the differential pressure in order to get close to it?
The setting range of the differential pressure transmitter depends on the selection of the primary throttling element, the V-cone; its size is specified in the technical data. Although the transmitter’s range can be increased, its accuracy cannot be guaranteed, and it becomes meaningless if the range is set too high. ,
So, in order to reflect the current installation conditions and get a more accurate representation of the flow rate, isn’t it necessary to set an appropriate range for the differential transmitter?
The differential pressure range specified in the V-cone flowmeter manual is 9.8 kPa; there should also be a field indicating the maximum flow rate in tons. The value of 9.8 kPa should be set as the range for the transmission, while the maximum flow rate in tons should be set as the range for the DCS. As long as the operating conditions deviate not significantly from the design values, the measurement results will not differ much. Reputable manufacturers of V-cone flowmeters generally calibrate them by simulating the design conditions at the time of production.
This post was last edited by cqdfwy on 2017-3-7 at 16:02. As mentioned earlier by “Sikong Zhaixing” on floor 7, the setting range of the differential pressure transmitter depends on the selection of the primary throttling element, the V-cone; its size is determined by the specifications. The poster should keep in mind that the set range of the transmitter is not arbitrary; even if you manage to determine the current flow value, any change in production conditions that leads to a change in flow rate will render that value invalid. Therefore, it is still necessary to follow the specifications. Also, be sure to set the correct range for the transmitter; don’t forget that the range set on the DCS should correspond correctly as well. For example, if the differential pressure range specified in the V-cone calculation sheet is 9.8 kPa, then the setting range for the transmitter will be 9.8 kPa; likewise, the range set on the DCS (if it is a differential pressure value) should also be 9.8 kPa, rather than 36.3 kPa. Of course, if more accurate measurements are required, temperature and pressure compensation as well as calibration techniques are indeed needed to assist.
Take the square root on either the transmitter side or the DCS side, but only one of them can be used for this operation.