Guided wave radar level gauge maintenance method
1. Radar level gauge installation and performance requirements:
Oil tank radar level gauge for liquid level detection; full name intelligent guided wave radar level gauge, is the product of Jiangsu Hongrun Instrument Co., Ltd., all installed on the top of 8000m3 and some 4000m3 oil tank, model HR-ZLD series, Two-wire instrument, zui large measurement error ± 3mm; resolution is ± 0.03c / o of measurement distance; response time is 1 second; ambient temperature requirement is -40 ~ +80 ° C; measurement output is a standard 4 ~ 20mA current signal.
two. Introduction to the working principle of radar level gauge:
The level measurement of vegetable oil tanks is done by a guided wave radar level gauge. It is a “top view†measuring instrument based on the principle of time and travel. The true measuring distance of the meter is the distance from its reference point to the surface of the material, that is, the distance from the flange of the meter to the surface of the oil to be tested. Its working principle is:
The high-frequency pulse is emitted by the instrument probe and propagates down the cable. When the surface of the oil is reflected back, it is received by the receiver in the instrument, and the measured distance signal is converted into the liquid level signal of the oil through the internal calculation of the chip. .
Wherein, the measuring distance D of the meter is proportional to the time taken for the pulse to be transmitted to be received;
The formula is: D = C × t / 2 (C is the speed of light)
If we refer to the known tank empty tank value (reference point to the bottom of the tank) by E; the oil level in the tank is indicated by L; the radar measuring distance is represented by D, then the relationship between the three is:
L=E -D
three. Tank level signal transmission method:
The standard 4~20mA liquid level current signal is transmitted by the guided wave radar level gauge to the PLC analog receiving module on the site through the shielded twisted pair cable, and then the liquid level signal is transmitted to the oil control room control room by the ControlNet network distributed in the tank area. PLC host, interface display.
four. Common fault phenomena:
The PLC interface shows that the liquid level does not match the value of the commodity inspection.
Fives. Troubleshooting process:
1 . First check whether the tank top radar level gauge oil level full set value is consistent with the liquid level set value in the PLC program. A common phenomenon is that the parameters set by the two are different, resulting in inaccurate interface display.
2 . Check that the radar level gauge itself shows a problem. The method is: through the liquid crystal display VU331 on the radar level gauge, the instantaneous liquid level of the tank and the current output value under the instantaneous liquid level are observed, and the corresponding full current value is set by the radar liquid level meter full liquid level value. Proportional relationship, calculation, check whether the instantaneous current value output by the tank's instantaneous liquid level value is accurate. If there is an error, the radar level gauge itself has a problem and further inspection of other internal parameter settings is required. If there is no problem in checking the setting of each parameter, the radar liquid temperature meter maintenance department should solve the related problems. The radar level gauge is a valuable precision instrument. When the cause of the fault is judged, it is forbidden to disassemble it.
3 . Check the signal transmission line for any problems. When the radar level gauge oil level full set value is consistent with the liquid level set value in the PLC program, if the signal transmission line works normally, you should see that the liquid level instantaneous height value on the radar level gauge VU331 should be the same as the PLC. The interface display values ​​are consistent; otherwise, it indicates that there is a fault in the signal transmission line, and the fault detection of the radar level gauge to the on-site PLC module twisted-pair shielded wires, connectors and related ControlNet network should be performed one by one.
4 . When the radar level gauge and the PLC interface display the same value, but there is always a difference with the commodity inspection scale value, then after eliminating the above various faults, the radar level gauge internal parameter empty height value can be adjusted to solve. Because the air level of the radar level gauge is a fixed value, if the original input data is measured incorrectly.
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