E+h mass flow meter
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The operation instructions for the E+H mass flow meter mention an output density; it is necessary to set the density corresponding to 4 ma and the density corresponding to 20 ma. What does this mean? ? By default, 4ma is set to 900 and 20ma to 1300. Isn’t density a constant? Why is it still necessary to set the value of 4mA and the value of 20mA?
For a pure substance, the density can be considered a constant, but it generally refers to the density at a specific temperature that has been designated or agreed upon according to certain standards. The density of a liquid changes with temperature; in the case of mixtures, the density also varies depending on the composition. The density changes in binary systems are relatively simple, while there are more factors affecting the density in multi-component mixtures. Therefore, the output signal for the density value needs to be defined based on the specific application, with 4mA generally being set as the lowest possible density value. If it is a gas, the change in density is more complex.
Measurement is simply measurement; it passes through sensors and transmitters, and the resulting signal is what is transmitted. For signal transmission, it’s necessary to set a range so that the signal can be sent to a DCS or another system for reception – in other words, it’s just a matter of specifying a range
This transmits the density to the host computer via current communication; the 4-20mA signal output works in this way: the flow meter generates a current value, which is then received by the host computer and converted into the corresponding density value. Each current value corresponds to a specific density. By default, if the flow meter measures a density of 900, it will output a current of 4mA. When the upper-level system receives this 4mA current, and if the corresponding density as per that 4mA value is 900, then the value will be converted to 900; if it is 700, then it will be converted to 700. There’s no need to go into the specific calculations; in short, the density corresponding to 4 and 20mA signals from the flow meter and the host computer must be the same.