Problem with DCS displaying motor current
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A pump needs to display the current on the DCS. The current transmitter has an input range of 0–5A and an output range of 4–20mA. The transformation ratio of the current transformer is 200:5. How should the range be set at the DCS end? Is it set based on the ammeter in the on-site electrical cabinet, or is there some other basis? How is it calculated? Is there any formula or something?
This post was last edited by Ku Liang Zhi Le on 2021-7-21 at 16:21. 1. The current transformer ratio is 200:5; 200/5 = 40. 2. The current on the secondary side of the transformer being 5 A corresponds to a primary side current of 5 * 40 = 200 [A]； 3. The current transmitter: 4 mA corresponds to a primary current of 0 [A], while 20 mA corresponds to a primary current of 200 [A]. 4. The input current on the DCS side: I = A * 16/200 + 4 = 0.08*A + 4.
Forgive my ignorance; I’m not very familiar with electricity. What does the ‘A’ here represent – the rated current? And what does 0.08 mean?
(20-4)/(200-0)=16/200=0.08
It means dividing 16mA (20-4) into 200 parts; in other words, determining how many mA of signal current corresponds to each A of current
The range on the DCS side is set to 0–200A, so the current value is displayed on the DCS interface accordingly.
This post was last edited by brevon on 2021-7-27 at 10:29. The range of DCS is simply 0-200A; there’s no need to calculate it – it’s just the rated current on the primary side of the current transformer. The middle stage is also a conversion process: 200 rotations correspond to 0–5A, and 5 rotations correspond to 4–20mA