Seeking help with compensation issues for ultrasonic flowmeters
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The gas being measured is delivered to the site using an NM3/h flow meter; temperature and pressure compensation can be set on this meter, but it is not possible to measure the actual P&T values in real time. The current setup at the site is as follows: the measurement range is the same as that of the DCS, namely 0-570000 NM3/h. The pressure and temperature values during operation are set to 3.17 MPa and 32°C respectively. In the DCS, temperature and pressure compensation is applied to the range of 0-570000 Nm3/h, with P=3.375 and T=32℃
Congratulations, congrats – you couldn’t guess it. . . No explanation.
If you have a compensation formula, all you need is the velocity flow rate or even just the flow speed; you can then use that to calculate the temperature and pressure on that pipeline directly in the DCS. If his gauge supports setting the temperature and pressure in the header, it can be directly converted into flow rate under standard conditions.
If a gas ultrasonic flowmeter has undergone temperature and pressure compensation, the flow rate is converted to standard conditions and output as 4-20mA – why does the DCS still need to perform further compensation? Gas ultrasonic flowmeters are so expensive – why go for manual compensation? Why not install pressure sensors and temperature sensors for real-time compensation?
Temperature and pressure compensation can be set in the flow meter, but it cannot measure the actual P&T values in real time; since there is no real-time measurement of temperature and pressure, how can compensation be achieved on-site? That’s not funny at all
Generally, temperature and pressure measurements are included in flowmeters in order to perform temperature and pressure compensation; if such measurements are not available and only internal data is used, the results will not be very accurate. It is recommended to carry out temperature and pressure compensation on the DCS, as this makes it easier to do so
It can be set, but it’s set to a fixed value
What you say makes a lot of sense. The reality is that real-time PT cannot be measured inside the gauge; so what should be done in such a situation to obtain accurate results?
Compensating the on-site \"standard volume\" further based on real-time temperature and pressure results in real-time standard volume.
The problem is that your flow meter does not have temperature and pressure measurement functions. Are there any temperature and pressure measurement points elsewhere in your pipeline? If so, you could consider using those values. If you don’t want to use those values either, and the pipeline’s temperature and pressure data are already available in the DCS system, then you can use the DCS to calculate the temperature and pressure compensation factors. If there are measurement points available, I can provide you with the formulas; I’m waiting for your reply
This post was last edited by cqdfwy on 2018-7-24 10:57. 4#Didn’t I already say that? “Why not install pressure sensors and temperature sensors for real-time compensation? ”. When the flow meter allows the input of temperature and pressure signals (since it has temperature and pressure compensation functions, it should be able to accept such signals), external signal sensors are used to measure the flow rate and provide supplementary data, so as to achieve accurate measurement ； If you set the temperature and pressure values directly in the flow meter for calculations, how can you ensure accurate measurements when those values do not match the actual operating conditions? This temperature and pressure setting is intended as a temporary replacement in the event of a failure of the temperature and pressure sensor, and it is not meant for long-term use. Temperature and pressure compensation has already been applied to your flow meter (whether using preset temperature and pressure values or measured ones), and what is output is the flow rate under standard conditions. Applying compensation again by the DCS constitutes redundant compensation, which is incorrect. Compensation can be performed at the DCS end only when the flowmeter outputs the operating flow rate (in M3/h, rather than NM3/h).