News

The principle and role of level gauges, common problems - focus on microfluidic control technology

The principle and function of the level gauge

The liquid level gauge is a pressure sensor for measuring liquid level. It is suitable for liquid level measurement of various media in petroleum, metallurgy, electric power, pharmaceutical, water supply and drainage, environmental protection and other systems and industries. Moreover, with the continuous growth of the domestic magnetic flap level gauge market in recent years, the development prospect of the level gauge sensor industry is very good.

The working principle of the liquid level transmitter is that when the two pressures of the measured medium pass into the high pressure chamber and the low pressure chamber, they act on the diaphragms on both sides of the δ element (ie, the sensitive element), and fill in the spacers and the components. The liquid is transferred to both sides of the measuring diaphragm.

The (floating ball) level transmitter consists of a capacitor consisting of a measuring diaphragm and electrodes on the insulating sheets on both sides. When the pressures on both sides are inconsistent, the measurement diaphragm is displaced, and the displacement is proportional to the pressure difference, so the capacitance on both sides is not equal, and is converted into a signal proportional to the pressure through the oscillation and demodulation links. Pressure transmitters and absolute pressure transmitters operate on the same principle as differential pressure transmitters, except that the low pressure chamber pressure is atmospheric or vacuum.

The A/D converter converts the current of the demodulator into a digital signal whose value is used by the microprocessor to determine the input pressure value. The microprocessor controls the operation of the transmitter. In addition, it performs sensor linearization. Reset the measurement range. Engineering unit conversion, damping, square root, sensor trimming and other operations, as well as diagnostic and digital communications.

This microprocessor has a 16-byte program RAM and has three 16-bit counters, one of which performs A/D conversion.

The D/A converter fine-tunes data from the microprocessor and the corrected digital signal, which can be modified by the transmitter software. The data is stored in the EEPROM and remains intact even if the power is turned off.

The digital communication line provides the transmitter with a connection interface to an external device such as the Model 205 Smart Communicator or a control system using the HART protocol. This line detects the digital signal superimposed on the 4-20mA signal and transmits the desired information through the loop. The type of communication is frequency shift keying FSK technology and is based on the BeII202 standard.

Then, explain the three level gauges for everyone
1, float level gauge:
Float type level transmitter is to change the magnetic float to buoy, the liquid level meter is designed according to the Archimedes buoyancy principle. Float type liquid level transmitter uses tiny metal film strain sensing technology to measure liquid level, boundary level or density, and it can perform routine setting operation through on-site keystrokes during work.
2, float level gauge:
Float level transmitter consists of magnetic float, measuring catheter, signal unit, electronic unit, junction box and mounting parts. Generally, the proportion of magnetic float is less than 0.5. It can be floated above the liquid level and along the measuring catheter. Move, the catheter is equipped with a measuring element, which can convert the measured liquid level signal into a resistance signal proportional to the change of liquid level under the action of external magnetic and convert the electronic unit into 4-20 mA or other standard signal output.
3, static pressure level gauge:
The transmitter works with the measurement principle of hydrostatic pressure. It uses a silicon pressure measuring transducer to convert the measured pressure into an electrical signal. It is then amplified by the amplifying circuit and compensated by the compensation circuit. Finally it is 4-20 mA or 0-10 mA. Current mode output.
The use of level gauges is relatively extensive, which has brought tremendous impact on our lives and work. In order to correctly use the level gauges, we need to understand their classification.

Frequently asked questions and precautions

The level gauge is the pressure formed by two levels of high and low (the vapor condenses into a liquid through a small steam drum). It is sent to both ends of the diaphragm of the detection part of the transmitter, detects the differential pressure, and then converts the current to 4~20mA. The signal is output to the DCS host and is calculated and converted back to the liquid level signal to the CRT. When the CRT is unable to control the system's water supply due to incorrect values, it should go to the site to check, check and adjust the actual water level. Input pressure diaphragm sensor capacitance change detection section measurement circuit calculation amplification circuit output current transmission section.

Specific steps are as follows:
1. Open the two drain holes on the upper end of the transmitter for steam exhaust, because the central control liquid level signal is distorted.
In addition to the failure of the transmitter itself, generally the detection medium contains bubbles or impurities causing deviations in the detection signal, so open the two drain holes on the upper end of the transmitter for steam discharge until there is continuous liquid ejection. When this step adjusts the drum level, it should be noted that the control center will switch the drum level control to another standby control level (LI404 and LI405 for PH furnaces and LI304 and LI305 for AQC furnaces) to prevent The control liquid level value has a large and severe fluctuation, which causes the automatic control to fail. In addition, when the level of the flash evaporator is adjusted, since the flash evaporator is a single-series liquid level gauge, adjustments should be made more slowly and with care.

2. If the adjustment result of item 1 is not good, open the drain valve on the transmitter piping to discharge the pollutants in a small amount. When this task is performed, pay attention to the safety of operation. The valve should be opened slowly to prevent possible steam burns.

3. If the on-site glass water level gauge differs greatly from the central control liquid level value, it cannot be determined that the on-site glass water level gauge should be flushed and adjusted to prevent the on-site glass water level gauge due to soda water. The level of the liquid level in the field caused by mixing or valve plugging is distorted.

note:
1. In the inspection process results, make sure the medium is liquid. 2. The liquid liquefaction into the liquid for a certain period of time, do not rush and tamper with the valve.
3. After confirming that the drain valve is closed, no liquid flows out.
PH drum level count: -700mm~+700mm AQC drum level count: -450mm~+450mm NO.1 flasher level count: -1000mm~+600mm NO.2 flasher level count :-1000mm~+600mm

PREVIOUS：Pressure Transmitter Installation and Usage CNEXT：Throttle Flowmeter - Focus on Microfluidic Co