Interpretation of DCS Configuration (ECS700)

I’ve never used 700; I’ve only used 300. For programming, I don’t use ladder diagrams or function block diagrams, as they are too cumbersome and take up a lot of space. Instead, I use the text-based functions available, programming in a language similar to ST. If this is a built-in functional block of the system, click on it and follow the help instructions for an explanation, or press the F1 key. It could also be a custom-designed functional block or function.

For a liquid with a cross-sectional area of S, a height of h, and a density of ρ, its own weight is S*h*g*ρ; thus, the force acting on the cross-sectional area is also S*h*g*ρ, while the pressure is h*g*ρ. In the case of a tank used to store a liquid of a certain density, the pressure at the bottom of the tank – compared to the pressure at the liquid surface – is proportional to the liquid level. If the liquid stored is water with a density of 1000 kilograms/m3 and the level is 1.6 meters high, then p = h*g*ρ = 1.6*1000*10 = 16000 Pa. In the case of a differential pressure transmitter, we simply need to set the upper and lower limits of its measurement range to 0-16 kilopascals. Then set the upper and lower limits of the range for the tag value to 0 and 1600 mm. If there are two pressure gauges, then create a new variable for the pressure difference; this variable will represent the difference between the two pressure gauges. Next, create another variable for the liquid level, with the value of the liquid level in meters being equal to the pressure value in Pa divided by the liquid density and then divided by 9.8.

It’s the block I wrote myself; just go in and take a look to find out

I didn’t write it myself; I found that the level calculated based on the indirect pressure difference does not match the level indicated by the radar. So ask him about the calculation logic of this program.

To go inside the block and take a look, this isn’t a standard block; it doesn’t indicate that it was created by you

The issue of discrepancies between the differential pressure level and the radar level requires calibration in order to standardize the 0% and 100% points. In the image you sent, a value of 0 is shown below the red line; this level cannot be measured using differential pressure, but it can be detected by the radar level gauge. Whether it is displayed as a negative value or not depends on how it’s specified in your DCS

This post was last edited by Xin Chang Xiao Xu on 2024-7-4 20:16. The differential pressure algorithm uses the pressure gauge below as a reference, with the surface where this gauge is located being considered the 0 liquid level. If this pressure gauge is placed at the bottom of the tank, the plane of the tank bottom is used as the 0 liquid level. If you place the pressure gauge below at a height of 500 mm, then the calculated value will need to have 500 mm added to it. The formula P=ρgh cannot be used directly; there is a slight difference, as this formula applies when the liquid level is constant – for example, when it is at full level – and it indicates that the pressure at different depths within the liquid varies. My previous derivation of the formula was based on the fact that pressure is generated by the weight of the liquid itself, along with the additional pressure at the surface of the liquid; this combination yields the pressure indicated by the gauge. Liquids at different levels reach different heights above the lower pressure gauge, resulting in different gravitational forces and thus different pressures. For the two pressure gauges, diaphragm-type gauges should be used. If there is a height difference between the gauge and the diaphragm, the oil used to transmit pressure has a density, which will result in an additional pressure load; in such cases, correction is necessary. For example, at a liquid level of 0, if the difference between the two pressure gauges is not zero, this value must be subtracted when calculating the pressure difference. For radar level gauges, it is necessary to set the distance between the probe and the lowest liquid level correctly. When there is liquid present, the distance traveled by the radar can be calculated based on the time interval between signal transmission and reception sowie the speed of sound; half of this distance represents the gap between the probe and the liquid level. The height of the liquid level is then obtained by subtracting the distance between the probe and the liquid level from the value set.

You can check the module definitions and pin descriptions of the center console

Yes, it depends on the calculations related to pressure difference. When the value is below 500, it’s unclear what the rules for those calculations are. Our system engineers say that there’s nothing special involved; it’s simply H=P/meat *G. My question stems from the program itself. I don’t understand it, and it seems like what the other person said isn’t quite accurate either