Fukushima installation
Figure 1: The arrangement of the level transmitter (LT) in the reactor vessel at Fukushima, according to Dr. Ritsuo Yoshioka, president, Japanese Functional Safety Laboratory.
In my correction of this level control loop, I added a second DP cell (āPT in Figure 2) that is continuously detecting the height of the level in the wet leg (A in Figure 2). If, for any reason, the height of this reference leg is dropping, the amount of drop is added to the the output signal of the level transmitter (LT in Figure 2).
Naturally, in your applicationāif youāre sure that the wet leg will always be there and will always be of constant heightāyou donāt need the correction I made in Figure 2 for the Fukushima reactor. In your case, you can just reverse the pressure taps or use a reverse-acting transmitter.
BƩla LiptƔk
[email protected]
A: Itās very difficult to help you with the minimal detail you provided. However, if we review some general details of level measurement, maybe you can understand some of the difficulties in using differential pressure to measure liquid level.
In Figure 3, the pressure at the top of the tank must be presented to the DP level transmitter (LT) through an impulse line. The impulse line is not empty. It may be filled with a non-corrosive fluid designed for this purpose, or it may be filled with condensate of the fluid in the tank being measured. For that reason, I labeled this tubing as āwet legā in the drawing. Likewise, the pressure at the bottom of the tank is also presented to the LT via its impulse line (not labeled in the figure).