The cause of this failure is mostly water beads or dirt under the radar level gauge transmitting antenna or isolation window. Remove the level gauge, use a clean, soft cotton cloth to dry the antenna or under the isolation window of water or dirt, restart can generally return to normal. To scrub the transmitter antenna of the level meter, scrub it with a soft cotton cloth dipped in alcohol, gasoline and other solvents, and do not scrub with alkaline solvents. The causes and treatment methods of transmitting antenna fouling are as follows. ① The water droplets formed after the steam cooling in the container are attached to the transmitting antenna, hindering the emission of microwaves. Isolation devices can be used, and some factories use Teflon isolation devices, and have achieved better results. The material not only does not hinder the emission of microwave, but also plays an isolating role. After the isolation device is installed in a certain way, the steam in the container can be isolated from the transmitting antenna, and the condensate water attached to the isolation device can be distributed in a certain form after formation, so as not to affect the purpose of microwave emission. ② When the equipment uses the mixing motor, the slurry is thrown, so that the installation sleeve and the transmitting antenna are dirty and scaled. As long as the stirring motor turns, it will raise the slurry, which is unavoidable. The scaling problem can be solved by increasing the diameter of the casing. The scaling degree of the day diameter casing will affect the emission wave in a much longer time than that of the small diameter casing. When the scale of large diameter casing reaches a certain degree, part of the scale will fall off under the action of gravity. (3) Non-standard installation of the level gauge will also cause the fault, the antenna does not extend the sleeve, the diameter of the sleeve is too small, the pipe wall is rough and there are welds, etc., which may cause more interference echoes. Usually, the upper blind area can be increased, and the parameters can be set by the full tank processing function of the instrument. If it does not work, consider repositioning the installation.
④ When the scale or dirt on the antenna is small, the echo intensity will be weakened, and only occasionally jump to the maximum. Usually take power off restart; Or use the echo re-search function, from the multiple echo list measured by the instrument, select the echo that is close to the actual liquid level as the surface echo, it is possible to restore the instrument to normal. When scale or dirt accumulation on the antenna is serious, the intensity of the echo may be lower than the threshold value. It is better to set the threshold value to 20% of the surface echo under stable conditions. If it cannot be restored by software treatment, only remove it and clean the dirt or dirt on the antenna. Antenna fouling or dirt is a common problem, regular cleaning of antenna fouling and dirt, will greatly reduce this kind of failure.
The liquid level is normal, and the display fluctuation can be solved by modifying the time constant and increasing the damping time of the instrument. There is condensation or water beads on the antenna, the mixer makes the surface of the measured liquid level fluctuate sharply, and the liquid level gauge is installed above the discharge port, which will enhance the interference echo in the container and cause the liquid level display value to fluctuate. There are condensation water beads on the antenna, you can take the power off and restart the method to try, if there is no change, you can only remove the transmitter head, wipe the condensate on the antenna, or search for the echo again. When the display fluctuation is considered the most is poor line contact, electromagnetic interference, electronic circuit problems; However, do not ignore the impact of the display instrument or DCS card, such as some DCS card with insufficient load capacity, there will be normal process liquid level, but the instrument display value frequently fluctuate. Sometimes the card may be restored to normal, otherwise the channel or card should be replaced.
When the container will be emptied or will be full, the instrument will still output a signal that is obviously inconsistent with the liquid level change, for example, when the liquid level in the container will be full, it will still show a low liquid level value. The causes of the fault are as follows. ① Antennas or antennas near the attachment, will produce interference echoes. Too much dirt accumulated on the antenna will strongly reflect the microwaves, causing the meter to display a fixed high level. By cleaning the antenna and the dirt and attachments near the antenna, and wiping the transmitting antenna, most faults can be eliminated. There are obstacles or fixed objects in the tank, resulting in a strong reflection of the microwave, and the value of the echo intensity is larger at this time. Most of the failures occur in the empty tank state, the first trial software processing, the purpose is to suppress interference echoes, shield false signals. To register the interference echo, the echo measured at present is registered in the echo list as a false echo, after registration, obstacles or fixed objects in the tank will cause interference echo; Or use the "near field suppression" function to eliminate the fault, by setting the near field suppression distance, so that the instrument will register the echo in this range as not to measure the disturbed echo. The effect is better when there is a hanging material near the weld, antenna or antenna of the mounting flange. The most effective measure is to re-select the installation location of the instrument, or contact the technician to rectify the obstacles or fixed objects in the tank to eliminate the occurrence of failure.
When the liquid level is displayed as a fixed deviation, first check whether the tank height is set correctly, so that the zero point of the instrument is consistent with the reference zero point of the process. It should also be checked whether the scale level is the same as the measuring range of the upper computer, and when the measuring range of the display instrument is not known, such as VFO3 level meter can be solved by dynamic setting (F11) test function, so that the transmitter output 4mA and 20mA query respectively. First verify the height of the tank, and then check that the basic parameters are set in accordance with the height of the tank. Power off and restart to try whether it can return to normal. If it does not return to normal, only remove the transmitting head to check whether there is condensation water on the antenna. If there is condensation water or dirt, clean and wipe it, and then install it to observe whether it is normal.
When the liquid level displays the minimum empty tank, the display value is not zero, such as the 5600 instrument will display the "Invalid" wave loss alarm, mostly the radar surface echo signal is lost when the tank is empty. Display panel can be used to re-search the echo; Or use the empty tank handling function of the instrument to deal with the loss of surface echo near the bottom of the tank. If the surface echo is lost, this function will cause the transmitter to display zero liquid level. The actual range of the instrument is too small, the echo signal is lost when the tank is empty, and the range should be re-verified, or a larger antenna should be selected. Sometimes the process level is about to fill the tank, but the instrument shows a very low level, which is due to the increase of multiple echoes in the tank when the level rises, and the instrument recognizes a beam of echoes with a larger time travel as the measurement echo, resulting in incorrect calculation results. The field suppression distance should be modified and the false signal should be presented to eliminate the influence of multiple echoes.