Are the calculation results correct? Do I need to subtract 4MA?
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The transmitter’s measurement range is 0–33.33 KPa, with a corresponding flow rate of 0–320 m3/h. What is the differential pressure when the transmitter outputs a signal of 12 mA? What is the corresponding traffic volume? Solution: The relationship between the differential pressure signal and the output signal of a differential pressure transmitter is given by ΔP·ΔI = ΔPmax·ΔImax; thus, ΔP = 12 – 4/20 = 33.33/20 = 16.67 KPa. The relationship between flow rate and the output signal is given by Q/Qmax = ΔI/ΔImax; therefore, Q = 8/16 × 320 = 227.2 m3/h. When the differential pressure transmitter outputs 12 mA, the differential pressure is 16.67 KPa, and the flow rate is 227.2 m3/h. My question is: should 12mA be reduced by 4mA? Is it only when the multimeter reads an MA value that 4MA is subtracted? Thank you! ! !
The flow rate is proportional to the square root of the differential pressure; you first need to determine whether it is the transmitter that performs the squaring or the DCS.
I am dealing with the square root of DCS values; how is it calculated for transmitters? Thank you! ! ! ! !
It’s simplest to use the square root function for the transmitter: 4-20mA corresponds to 0-320 m3/h. So, flow rate = (320–0) / (20–4) * (12–4); SQ(differential pressure) = SQ(33.33) / (20–4) * (12–4)
I understand what it means to take the square root of a transmitter value; could you explain what taking the square root does in a DCS system? Is the current then proportional to the pressure difference or flow rate?
The square root in DCS means that the flow rate is proportional to the square root of the differential pressure; the differential pressure, on the other hand, is directly proportional to the current under all circumstances.
DCS square root: Differential pressure is proportional to 4-20mA. It is proportional to the square root of the flow rate and differential pressure, or the square root of 4-20mA. 4-20mA corresponds to 0-33.33kPa. Differential pressure = (33.33-0)/(20-4)*(12-4). Flow rate = (320-0)/SQ(20-4)*SQ(12-4)
The output value is 12MA; 4MA must definitely be subtracted during calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generally, for differential pressure type flowmeters, the output current signal and the flow range are set at the time of manufacture. When calculating, the actual current signal should be reduced by 4 mA.
The square-root current of the transmitter is proportional to the flow rate, and it is proportional to the square root of the differential pressure, right?
When the transmitter performs square root processing, current, flow rate, and differential pressure are all proportional to each other; this is because the square root operation has already been done inside the transmitter. As for the DCS performing square root processing, it’s as explained on the seventh floor.