The correct selection method of electromagnetic flowmeter lining material and common troubleshooting
Author:vacorda Source:vacorda.com Date: 2018-05-15 10:20:52
The electromagnetic flowmeter has a complete, electrically insulating liner on the inside of the measuring conduit and on the flange sealing surface. It is in direct contact with the liquid to be measured. Its role is to increase the corrosion resistance of the measuring catheter and to prevent the induced potential from being short-circuited by the metal measuring conduit. This plays a very crucial role.
How should the liner material be selected?
The lining material should be selected according to the corrosivity, abrasion and temperature of the measured medium.
1. Natural rubber (Soft rubber)，can measure the water and sewage.
a. Good elasticity, wear resistance and tearing force;
b. Resistant to the general weak acid, weak alkali corrosion.
2. Acid rubber (Hard rubber), can measure the general acid, alkali, and salt solution.
Resistant to hydrochloric acid, acetic acid, oxalic acid, ammonia, phosphoric acid and 50% sulfuric acid, sodium hydroxide and potassium hydroxide at room temperature, but not resistant to strong oxidants.
3. Neoprene (Neoprene), can measure water, sewage, mud and pulp.
a. excellent elasticity, high breaking force, good wear resistance;
b. resistant to general low concentrations of acid and alkali, salt solution corrosion, but not resistant to oxidizing medium rot <80°C.
4. Polyurethane rubber (Polyurethane), can measure the neutral strong wear of coal slurry, mud and pulp.
a. Excellent wear resistance;
b. Poor acid and alkali resistance <40°C.
5. Polytetrafluoroethylene (PTFE), can measure the concentration, concentrated alkali strong corrosive solution and sanitary media.
a. Boiling resistant hydrochloric acid, sulfuric acid, nitric acid, aqua regia, concentrated alkali and various organic solvents;
b. Good wear resistance, poor adhesion -80°C ~ +180°C.
Common Faults - Typical Troubleshooting and Handling
1. No flow output. Check if there is a fault in the power supply section, test the power supply voltage is normal, test the fuse off, check whether the sensor arrow is in line with the flow direction of the fluid, and replace the sensor installation direction if it is inconsistent; check whether the sensor is full of fluid, if there is no full fluid, replace the pipeline or install it vertically.
2. The signal is getting smaller or smaller. Test whether the insulation between the two electrodes is broken or short-circuited. The resistance between the two electrodes is normally between 70Ω and 100Ω. The inner wall of the measuring tube may be dirty. The electrodes should be cleaned and wiped. Do not scratch the inner lining. Measure the lining of the tube for damage and replace it if it is damaged.
3. Instability of the zero-point. Check whether the medium is full of air bubbles in the measuring tube and medium. If air bubbles exist, add air trap upstream. If it is installed horizontally, it can be changed to vertical installation. Check if the instrument grounding is in good condition. Conduct three-level grounding (grounding resistance ≤ 100Ω); check that the conductivity of the medium is not less than 5μs/cm; check whether the medium is deposited in the measuring tube and be careful not to scratch the lining.
4. The flow indicator does not match the actual value. Check whether the fluid in the sensor is full of tubes, with or without bubbles, if there are air bubbles, install an air eliminator upstream; check whether each grounding condition is good; check whether there are valves upstream of the flowmeter; if so, move to the downstream or make it fully open. Check whether the converter range setting is correct. If not, reset the correct range.
5. The indicator fluctuates in a certain range. Check if the environmental conditions change, such as new interference sources and other magnetic sources or vibrations that affect the normal operation of the instrument, remove the interference or displace the flowmeter in time; check the test signal cable, and perform end treatment with insulating tape. The conductors, the inner shield, the outer shield, and the housing do not contact each other.
The fluid of the electromagnetic flow meters measures must be conductive, so non-conductive gas, steam, oil, copper and other substances cannot use electromagnetic flowmeter.
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