Application of electromagnetic flowmeter in cellulose impregnation process

Case introduction

The application of electromagnetic flowmeter in cellulose impregnation process and common fault repair methods:

The application of electromagnetic flowmeter in the impregnation process of viscose liquid workshop introduces the structural points and working principle of electromagnetic flowmeter , the flow meter has a simple structure and high control accuracy. And introduced the maintenance experience of common faults of electromagnetic flowmeter.

The impregnation process of our company’s stock solution workshop consists of four parts: primary alkali application, meal feeding, secondary alkali replenishment and discharging. First, set the primary alkali amount according to the process requirements. The computer system calculates the primary alkali amount. The secondary alkali replenishment is calculated by the computer system based on the actual input amount of meal. The computer system calculates the secondary alkali replenishment ratio. The electromagnetic flowmeter uses the set value as the control target to measure the flow of the alkali solution.

Since the alkali ratio directly affects the cellulose impregnation effect and viscose quality, the measurement of electromagnetic flowmeter is even more important. Through our understanding of the working principle of Mingyu electromagnetic flowmeter, we can accurately avoid the occurrence of faults and solve them as soon as possible after they occur, ensuring that the measurement of electromagnetic flowmeters achieves the purpose of precise control.

1. Structural points and working principles of electromagnetic flow meters

1. 1. Structural points of electromagnetic flow meters

Our company’s impregnation process uses intelligent Square split four-button series electromagnetic flowmeter consists of two parts: electromagnetic sensor and converter. The electromagnetic sensor is installed on the industrial process pipeline. Its function is to linearly convert the liquid volume flow value flowing into the pipeline into an electric potential signal, and send this signal to the converter through a transmission line. The converter is installed not too far away from the sensor. It amplifies the flow signal sent by the sensor and converts it into a standard electrical signal output proportional to the flow signal for display, accumulation and adjustment control. The electromagnetic flowmeter is also designed with a Chinese LCD display with backlight and wide temperature. It is fully functional and practical, with intuitive display and easy operation, which can reduce the inconvenience caused by the English menu of other Mingyu electromagnetic flowmeters.

1.2 Electromagnetic flow, working principle of the meter

The measurement principle of the electromagnetic flow meter is based on Faraday’s law of electromagnetic induction. The side measuring tube of the flow meter is a short tube of non-magnetic alloy lined with edge material. Two electric currents pass through the tube wall along the diameter direction and are fixed on the measuring tube. When the excitation coil is excited by a bidirectional square wave pulse, a working magnetic field with a certain magnetic flux density will be generated in the direction perpendicular to the axis of the measuring tube. At this time, if a fluid with a certain conductivity flows through the measuring tube, it will cut the magnetic lines of force and induce an electromotive force. The electromotive force is proportional to the product of the magnetic flux density, the inner diameter of the measuring tube and the average flow rate of the fluid, that is, E=KBDV

In the formula: E - electromotive force (flow signal voltage between electricity)

B- Magnetic flux density

D--measuring tube inner diameter

V-average flow velocity

K-constant

Electromotive force (flow signal) is given by The electricity is detected and sent to the converter through the cable. The converter amplifies the flow signalAfter processing, the fluid flow can be displayed, and pulses, simulated current and other signals can be output for flow control and regulation. The figure below shows the working principle of the electromagnetic flowmeter.

2. Commonly used parameter settings

Instrument parameters determine the operating status, calculation method, and output mode of the instrument. Correct selection and setting of instrument parameters can make the instrument run in a good state and obtain higher measurement display accuracy and measurement output accuracy. The following are the parameter settings we commonly use in use.

2.1 Instrument range setting

The instrument range refers to the upper limit flow value (full scale) of flow measurement. The upper limit flow value is for the output signal and percentage display. It corresponds to the current output upper limit value, frequency (pulse) output upper limit value and 100% display value.

2.2 1-range automatic switching

The converter has an optional two-range automatic switching function, which can be easily used in automatic control measurement systems with a wide range of day and night flow changes.

2.3 Flow plate direction selection

If the fluid direction during debugging is considered to be positive but the instrument shows negative, set the flow direction to the reverse direction and vice versa.

2.4 Flow and zero point correction

The side measuring tube of the electromagnetic flow sensor is filled with conductive fluid, and the fluid is stationary and does not flow. The converter has already made a correction to the zero point of the Sanchang flow meter. Intelligent processing. If the zero point of the equipped sensor exceeds the intelligent processing range of the converter, flow zero point correction is required. The flow zero point is expressed by the flow rate, and the unit is m/s0

2.5 small signal cut-off point

The small signal cut-off point setting is expressed by the percentage flow rate of the measuring range. When you choose to allow small signal removal, the display and signal output of flow rate, flow rate and percentage will be cut off; when you choose to disable, no cutout will be performed.

2.6 Current output type

You can select 0-10mA or 4-20 mA analog current output in the current output type. The analog current output is internally powered by 24V and can drive a load resistance of 750,5 under the 0-20mA signal system.

2.7 Digital output

Digital output refers to frequency output and pulse output. Frequency output and pulse output use the same output point on the wiring, so in practical applications When selecting frequency and pulse output, only use one of them.

The frequency output is a continuous square wave, which is mostly used for digital instantaneous flow measurement and short-term total accumulation. The output range is 0-5000Hz. The flow percentage corresponding to the frequency output = flow value/full measurement value x frequency range. The frequency output method is generally used for control applications. The electromagnetic flowmeter used in the impregnation process uses the frequency output method.

The pulse output is a rectangular wave pulse train. By selecting the pulse equivalent, the volume value of the cumulative flow can be read out. It is mostly used for long-term direct volume unit total accumulation. Frequency output and pulse output are generally in the form of oc gate output. Therefore, it should be connectedDC power source and load.

3. Maintenance of common faults

Due to long-term operation of the electromagnetic flowmeter, some faults will occur, which will affect the normal use of the Sanchang electromagnetic flowmeter and bring losses to production. Fault manifestations are multifaceted. Below we will introduce our maintenance experience of electromagnetic flowmeters.

3.1 No flow output

Check whether there is a fault in the power supply part, test whether the power supply voltage is normal; test whether the fuse is on or off; check whether the sensor arrow is consistent with the fluid flow direction, if not, replace the sensor installation Direction; check whether the sensor is filled with fluid, if not, replace the pipe or install it vertically.

3.2 The signal is getting smaller and smaller or suddenly drops

Test whether the edge between the two currents is damaged or short-circuited. The normal value of the resistance between the two currents should be between 70 and 100 loon; inside the measuring tube Dirt may accumulate on the walls and should be cleaned and wiped without scratching the lining. Check whether the lining of the measuring tube is damaged. If damaged, it should be replaced.

3.3 The zero point is unstable

Check whether the medium is full of the measuring tube and whether there are bubbles in the medium. If there are bubbles, an air eliminator can be installed upstream. If the horizontal installation is installed, it can be changed to vertical installation. ; Check whether the instrument grounding is intact. If it is not good, it should be grounded at level three (ground resistance E100Ω); Check that the conductivity of the medium should be no less than 5us/cm; Check whether the medium is accumulated in the measuring tube. Be careful not to scratch the lining when cleaning. hurt.

3.4 The flow indication value does not match the actual value

Check whether the fluid in the sensor is full of the tube and whether there are bubbles. If there are bubbles, install an air eliminator upstream; check the grounding conditions Whether it is in good condition; check whether there is a valve upstream of the Mingyu flowmeter. If there is, move it downstream or make it fully open; check whether the converter range setting is correct. If not, reset the correct range.

The 3.5 indication value fluctuates in a certain range

Check whether the environmental conditions have changed. If there are new interference sources and other magnetic sources or vibrations that affect the normal operation of the instrument, they should be removed in time. Interference or displacement of the flow meter; check the test signal cable and use insulating tape to treat the ends so that the wires, inner shielding layer, outer shielding layer, and shell do not contact each other.