?For DCS, does the small-signal rejection function remove the differential pressure or a percentage of the flow rate?
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This post was last edited by zhaohh3211 on 2010-9-6 at 12:03. Differential pressure flow meters, such as orifice plates and VeriFlow meters, do not have temperature or pressure compensation; the 4-20 mADC differential pressure signal is sent directly to the DCS. The DCS has a function for removing low-level signals. I wonder whether this function removes a percentage of the differential pressure or a percentage of the flow rate – which one does the DCS you are using remove? Why cut the pressure difference? Why cut the flow rate? Is there a reason?
Either the differential pressure or the flow rate can be used; for differential pressure, 0.75-0.8% of the range value is sufficient, while for flow rate, 8-10% should be removed
ABE Systems: It’s convenient to compare differential pressures; simply set the LC value to the cut-off percentage in H_E
Zhejiang University’s system is also quite convenient; it allows for setting the percentage of signal to be removed, with 5% generally being the amount removed.
The cut-off flow percentage for Zhejiang University Zhongkong is generally 5%.
DeltaV seems to refer to the differential pressure; the original poster can perform the conversion, as flow rate is generally proportional to the value of the differential pressure. Thus, it’s possible to roughly determine how much adjustment is needed for the flow rate and how much for the differential pressure
This post was last edited by wangtosea on 2009-6-10 21:45; it generally refers to the percentage reduction in traffic. Small-signal clipping includes: linear clipping and zero-clipping. The reason for cutoff is that when the flow rate drops to a certain level (usually within 20% of the maximum flow rate, for example 10%), the flow rate is no longer related to the pressure difference in an exponential manner but rather in a nearly linear way; cutoff is necessary in order to maintain accuracy. Two parameters need to be set during cutting: the cut point (usually within 0~20% of the flow rate) and the cutting mode (linear or zeroing cutting).
The DELTAV system can also adjust the flow rate as a percentage; the maximum seems to be 30 percent. I tried setting it at 20 percent
Since there is a square-root relationship between differential pressure and flow rate, when the differential pressure is very low, the flow rate value becomes very high (the proportion of this flow rate value within the flow rate range). Therefore, small differential pressure fluctuations in air traffic control can cause significant changes in flow rate; to avoid this, it is necessary to perform small-signal rejection of the flow rate. Either differential pressure or flow rate will work; it’s just that the magnitude of the values is different.