Problems with Rosemount differential pressure transmitters

If the measurements are inaccurate all the time, could there be an error in the calculation of the migration amount? It is necessary to take into account the difference between the density of the isolation fluid and the density of the medium being measured.

Calculate the range and offset based on the medium density, the density of the isolation fluid, the distance between the high and low liquid levels, and the installation location of the transmitter, and then use the handheld device to check whether the settings are correct.

If this problem exists during the normal operation of the boiler, it is likely due to the instrument technicians using a too high value for the density of water during calibration; they should simply adjust the density value downward

Is it possible for the on-site level gauge to be inaccurate? We have encountered a situation where the liquid phase opening of this level gauge is low; after shutting down the system, inspection showed that the pipeline was almost completely blocked.

I think it’s probably an error in the instrument calibration; I need to do some proper calculations and check it out. For example, in terms of density, it’s around 600 when driving, while it’s 1000 when the vehicle is parked; that’s a 40% difference.

If this problem exists during the normal operation of the boiler, it is likely due to the instrument technicians using a too high value for the density of water during calibration; they should simply adjust the density value downward

The problem lies in the density of the water inside the boiler and the density of the isolation fluid; the density of water varies significantly with temperature.

Incorrect installation; there are issues with the point selection. Is the pressure on the sealed container eliminated? The original poster, take a look

It’s probably a problem with the range; the density of the fluid flowing through the boiler shell side doesn’t differ from the density of water by more than 40%

1. Is a two-chamber balance vessel being used? Is there any internal leakage? 2. Is the liquid level at the local measurement point the same as that at the remote measurement point? Sometimes, during boiler operation, the liquid level in the drum is not level. 3. When the drum is shut down, are the two liquid level measurements consistent? Are the measurement pipelines unobstructed? Please conduct a thorough inspection. 4. Is the transmitter set correctly?

Thank you all for your answers. After starting work today, the instrument worked properly again. The waste heat boiler I’m referring to is a device used in coal gasification; it has a tube side and a shell side. The tube side carries raw gas at a temperature of around 500 degrees, while the shell side contains medium-pressure boiler water. The likely reason for the problem is that at the start of operation, the liquid level in the shell side wasn’t full, so steam was always present on the negative pressure side of the transmitter. This led to an excess of gas in the pressure guiding tube on that side, resulting in inaccurate measurements. I’m not sure if my analysis is correct; I would appreciate any guidance from those with more experience. Thank you

There must be an issue with the parameter settings; carefully check them using the manual controller.

I’m not sure if your transmitters have experienced negative drift. If negative migration occurs, and you drain the liquid level in the negative pressure guide tube while the machine is stopped, or if the liquid level in that tube does not reach the required height (at the pressure sampling point of the negative pressure chamber), then the displayed value will be too high. If there is no liquid level at all in the negative pressure tube, it should display the maximum value. It can also explain the normal operation in this case: after the steam in the negative-pressure chamber condenses, the liquid level gradually rises to the pressure sampling point, and the migration amount reaches the set value, which is why it shows as normal. This exactly matches what you said. However, you still haven’t specified the range of this transmitter in KPa or the measurement range in cm. Could you please provide that information so I can determine what specific specific gravity should be used when measuring the liquid level in boilers? ,

12th floor; it seems the problem has been identified. The negative pressure side is filled with steam, and its low density causes measurement errors.

I don’t know what type of waste heat boiler the original poster is using What are the differences in their process media? If it’s just pure water for the boiler, why is an isolation fluid needed? As for the poster’s later guesses, they aren’t quite correct either, right? After the plant is shut down and the furnace is stopped, the isolation fluid in the transmitters or the liquid on the negative pressure side generally does not disappear or get automatically drained. What is the problem?

If it’s boiler water, salt removal should be done first, right? It shouldn’t cause blockages. After drawing out the water, it can be turned into condensed water using a condensation container, right? Is it still necessary to use an isolation fluid? What is this isolation fluid made of?

The density of waste gas vapor varies under different pressure and temperature conditions; it is necessary to determine the operating conditions and calculate the density accurately in order to obtain a precise liquid level reading. Generally, as long as the drift amount is properly calculated and the isolation fluid is filled to the proper level, there will not be a significant error with differential pressure transmitters

The density of water in a boiler varies depending on the water temperature.

First, it is necessary to determine whether the problem lies with the transmitter or the on-site level gauge. Using the transmitter, it is possible to check whether the zero point, range, and drift are accurate, as well as whether the installation on-site is proper, thereby addressing each issue one by one.

In addition to the recalculation of the range and migration based on the densities of water and steam as mentioned above, if we have the budget for it, it would be possible to use a boiler drum level gauge that can operate under all conditions (from cold water to steam generation). For example, the CAP-3031 series of intelligent capacitive level gauges from Beijing Kepost, or the radar level gauges from E+H designed for measuring boiler drum levels. Our unit has used both types of level gauges, and they have performed very well.