Fault issues with magnetic flap level transmitters
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The water storage tank in our company’s fire suppression pressure stabilization system is equipped with a magnetic flap level gauge; a level transmitter is also installed next to it, and it sends signals to the fire control room. There is a separate digital display for showing the level, as well as alarms for high and low levels that send signals to the fire control system. This morning, the reading was 0.52 (the normal level is 2.03), and an audio-visual alarm was triggered. I went to the roof to check the actual liquid level (as shown in the image), and it was at the normal level. Upon inspecting the junction box, no abnormalities were found. After tapping on the pipes connected to the level sensor, I went to the fire control room and found that the liquid level reading was 1.71. What could be the problem? What should the pipe that is connected to the level transmitter junction box and installed parallel to the magnetic flap tube be called? Is there a poor connection or obstruction in this tube (sensor)?
This is a reed switch-type level transmitter; it consists of reed switches and resistors as the electronic components. The transmitter converts the resistance value into standard signals such as 4–20mA, which are then sent to the digital display. Looking at the rod in your second image, there seems to be a small bracket attached to it, located at some distance from the cylinder. The version designed for normal temperatures can be attached directly to the cylinder with a flip plate; however, it’s necessary to remove it and conduct tests to see whether the output current of the transmitter changes linearly as the magnet moves from one extreme position to another ； Also, test separately to see if the digital display function is working properly.
Thank you. It has been working properly all along; I’m in Guangdong, and it hasn’t rained these past few days. There was some rain over a week ago, but it has still been functioning normally for over two years. Could this be related to an excessive amount of moisture inside the water sensor or reed switch?
Oh, take it apart and have a look. If there’s a problem with the seal, water ingress could also cause the issues mentioned above
Just replace it with a remote transmission rod (reed relay remote transmitter).
Remove the float from the flap and test it along the tube from bottom to top to see if the liquid level changes properly. If it’s not working properly, it’s a problem with the rod and the transmitter.
This post was last edited by Military Emblem 81 on 2019-10-19 at 21:16. The pipe connected to the transmitter on the outside of the flap level gauge contains a built-in reed switch (which is also a primary component of the remote transmission system); changes in the resistance of this reed switch are transmitted to the transmitter, where they are converted into electrical signals that are then displayed on the secondary meter. It is important that the pipe connected to the transmitter be in close contact with the pipe of the flap level gauge – too much distance between them hinders accurate measurement. Additionally, the float of the flap level gauge often gets stuck.
Tap on the float to check if the buoy is stuck; connect an ammeter in series and move the magnet up and down to observe the current. If the magnetostrictive element is too far away from the float, it’s possible that the magnet may not be able to detect it.
Just tie your tube directly to the thick tube of the magnetic flap. Remove that small bracket in the middle; take it off and discard it.
If the liquid level changes after tapping, it might be worth considering whether iron deposits on the float are causing it to get stuck
The float of the magnetic flap is a moving component, and the reed of the reed switch is also a moving component; since these are moving parts, errors in their operation are quite likely to occur. It was lucky that there were no false alarms in those 2 years. In the next 2 months, there will be one false alarm, or several false alarms over those 2 months – and that will become the norm. It was a false alarm. Just tap on the tube, or brush the magnet – it gives you something to do, which is better than just sitting around idle.:lol