The reason for causing the trouble of the electromagnetic flowmeter is numerous, this our host computer, to causing the electromagnetic flowmeter trouble source to make a brief analysis stemming from pipeline system and relevant apparatus, according to our summary, the trouble reason caused by pipeline and relevant apparatus mainly has the following six situations, they are:
1,It is not good to install;
2,Have not managed fully;
3,In charge of department’s storing and leaving the gas;
4,Sucking the gas constantly;
5,Reciprocating pump or controlling the valve to shake the pulsate that is produced and flow;
6,Use the flow regime change in the course.
The forms of expression of reason of these 6 kinds of troubles are not the same in the real work, some or even many kinds of reasons are mixed with causing the trouble together each other, so everybody is in the real checking process, should notice, want, accomplish, know what’s what to of various fields situation, as to to use the state know as many as possible pipeline, can discover the problems the most efficiently, solve the problem in the shortest time.
1,It is not good to install
The example that it is not good to be installed is as follows, ( 1) The flow sensor is matched with the internal diameter while connecting the pipelines improperly, it is too big to differ by, ( 1S091( 4: 1991 regulations: In a situation that there is no factory to recommend, the internal diameter of the union pipe can’t be less than the sensor internal diameter of the flow, no have big inch: 3% of the internal diameter ); ( 2) The washer dashes for ward people and circulates in the passway among flow sensor and pipeline; ( 3) Scratch and flow one and produce serious velocity of flow to is distributed distortion or rotates to flow in front of the neighbouring flow sensor, it is insufficient to in charge of section directly. These reasons mainly cause the measurement value of flow not to correspond to actual value, will export and rock too sometimes.
Although an embodiment of case is not that it was caused directly that the installation that the hereinbefore is exemplified is not good, but it is the same to enter and carry the washer to circulate in the passway it as the flow sensor for some reasons.
Shanghai one water plant and two stylographs connect DNl400 instrument in series and measure finished product water of factory out by two respectively, sent the side separately ‘ Water plant) Master with the take over party. Dissociate and all turn on about 5 meters of distance of butterfly’s valve and is about 2.5 meters apart from the second sensor of low reaches on the first sensor, in charge of a section of length to slightly dislike insufficiently directly in the upper reaches. Launched in 1997, found a pipeline and two instruments measuring value among them differed by 15%, difference was slightly reduced half a year later, it is 10%. Besides checking sensor measurement and is in charge of the internal state, have checked and analyzed in an all-round way, have not found out the trouble reason, has become the pending case. Unloaded the sensor and found that imported the cement lining block of the pipeline to loss until the second half of 1998, it highly reaches 300 at the place where the sensor is imported to pile up- 350mm (estimate) . These deposits result in entering the velocity of flow of sensor rivers and is distributed serious distortion, namely the pipeline underpart nearly has 0.25D high bow-shaped sectional barriers that has blocked the rivers. Remove the obstacle and return to normal promptly. As to the thing that difference is reduced from 15% to 10% half a year later, can interpret as piling up highly higher than 300- 350mm at the beginning, highly reduce under the erosion of flowing, difference, with reducing too. The heavy-calibre flow sensor unloads the pipeline or enters the pipeline to check inside, must stop flowing, involve a wide range of knowledge, can only usually be after the possibility to get rid of other troubles, put to go on finally.
2,Have not managed fully
Press insufficiently because of carrying or the sensor erection site of flow is bad, cause its measurement in charge of the inner liquid and fail to be full of, it has different manifestation because the symptom is not full of intensity and state of flowing. If a small amount of gas takes the form of and divides laminar flow or wavy to flow in the horizontal pipeline, the symptom is shown as the error increases, namely the measurement value of flow does not correspond to actual value; If it is a bubble to flow and flow or fill in the form and flow, the symptom, except that the measuring value does not correspond to actual value, will also export and rock because of hiding the surface of electrodes in the twinkling of an eye in gaseous phase. If the horizontal pipeline divides circulating in laminar flow the area gaseous phase part increases, namely the liquid has not been in charge of the intensity to increase fully, will also export and rock. If the liquid full tube gets on the liquid surface under the electrode, will export the ultra full degree of phenomena.
One shipyard of case 2 has an DN80mm electromagnetic flowmeters that measure the water flow, runs personnel reflect that it is zero hour to close the valve flow, output and reach the full degree of values instead. The site inspection finds only there is one section that is managed short in the low reaches of the sensor, water arranges the people atmosphere directly, it is it here sensor to install but stop valve it is upstream (such as? ? ? Position of 3 dotted lines 1) ,The sensor is measured and in charge of water-logging to all empty after the valve is turned off. Repack the valve to the position 2, the trouble is easily solved. The foot in the after-sale service example of reason of this kind of trouble is often met, it is engineering design by mistake.
3,In charge of department retention and gas
It is to fail to arrange and is only in charge of the inner air before launching to be in charge of a kind of reason of the gas of retention of department, remaining leaves the gas and is gathered and in charge of department’s culmination, is carried secretly by the liquid while flowing, take the form of the bubble to flow out; Carry the small bubble secretly to gather in another reason foot liquid gradually, retention is in charge of department’s culmination. The trouble is shown as the actual value of sum of measuring value of the flow is not accorded with and exported and rocked.
One petrochemical industry factory in Nanjing of case 3 guides water of the Changjiang River with DNl000mm pipeline, the pipeline long 10km rises and falls via the hillock along the terrain, carry and install DN700mm instrument in the hillock. In charge of department’s putting into operation, the electromagnetic flowmeter can’t work normally, there is abnormal phenomenon of rivers sound to find the electromagnetic flow sensor and adjacent place by the site inspection. Initial analysis thinks and in charge of department’s failing to arrange the inner air of the pipeline netly after launching, engineering design in high to decorate the vent valve and unable to bleed. Measure the electrode signal and is up to 4mV ‘ Majority electric potential) in order to interfere with ,Because can’t cut off the water and can’t further check and fix a breakdown. Factory’s maintenance personal follows up a case by regular visits to again several months later, no longer there is rivers sound at this moment, flow for some time, leave, leave air, take away with rivers, debug, can enable its normal running again.
One water plant in Guangxi of case 4 sets up the clear pond in the hilltop of suburb, utilizes high potential energy of the pond to send the finished water. Personnel reflect that sometimes the flow reveals unstably to measure DN700mm electromagnetic flowmeter of yield to run. Rock more than 10% of Damien to 20%, the error is great too, estimate that differs by about 20%. Examine and find that installs the flow sensor as shown in Fig. 7-9 in the pond live, it will be involved in the bubble that the water level is highly insufficient, even the flow sensor is measured and can’t be full of in the tube. If water level drop A to at the line, higher than suck mouthfuls of top, higher than, more, can produce swirl in the intersection of C and, involve in, form bubble the intersection of water level and superficial air, make it rock not to reveal; If the water level drops to B, measuring the tube will manage discontentedly. We propose that if pursue the dotted line and show and hold a elbow, expand the pond effective capacity, reduce the chance to suck the bubble, remedy the deficiency designed originally. This kind of embodiment is often met.
Fig. 9 is apt to be involved in the bubble and installed the example
5,Reciprocating pump or controlling the valve to shake to pulse and flow
The reciprocating pump pump sending liquid flows but the measuring point has not been far away from the pump, it will make the electromagnetic flowmeter export and rock to flow to pulse, sometimes will also produce and measure the error. In order to slow down the pulsating impact on instrument, can usually adopt and improve the electromagnetic flowmeter excitatory frequency or increase the Buddhist nun of the resistance; Can install damper units such as the angry room,etc. again in in charge of the departmenting. In charge of department’s flow control mismatch to make to control the valve will take shape and pulse and flow to shake too to open and close.
6,Use the flow regime change in the course
Usually will break down because of changing in flow regime too after the instrument is debugged for normal running one period. Though probability appears non- high in reason of this kind of trouble, should not forget this factor while analyzing the trouble reason.
5 this of case one hangs stripping lining slice in the liquid flow to swing, the rare embodiment of flowing flows and forms pulsing with the liquid. One copper mine Bin factory in Jiangxi is equipped with several electromagnetic flowmeters and measured the slurry including powdered firm looks, it is normal to use all the time in the past few years. Users reflected by July of 1998 an DN600mm instrument among them was outputted and rocked 50% – 100% up to the full degree of values. The site inspection instrument is normal, but also make an inspection tour and inquire that learns the power source of flowing to change at the end, will not produce and flow and fluctuate newly, has excluded the possibility of deteriorating and introducing interference newly in environment for use too. The overall impression is that an instrument is normal, installed and fulfilled requirements with the environmental condition. Because can’t stop flowing and unload and check the flow sensor and conceal some and neighbouring pipeline state at that time, have not found out the trouble reason for the moment. This factory parks the rifle is repaired until being monthly after me, find that divines and visits in the Model U tube lined with the rubbery lining in the sensor adjacent place of the flow, the large stretch of rubbery lining is lossed, hang in the tube, flow and swing with the liquid, cause and flow and fluctuate, the instrument reflects accurately, take shape and export rocking. It change U newly no matter after,it it is if you can’t rock, appear again to export by a wide margin.
Case 6 tortoise, in migration under tube, outputting signals presents the great spike, is this case taken from a foreign report? ? ? The heavy-calibre electromagnetic flowmeter that the foot takes place in U.S.A. monitors the condenser of thermal power plant to cool the sea water flow, see the big spike signal appears once in a while in the instrument from record sheet. Check live several times, because interfere with the noise and die promptly now in wink, can not catch while checking, have not found either that produce abnormal conditions such as electric noises,etc. around. User Zeng someone perhaps has idea that fish flow in the flow sensor to put forward, think, discharge door, have detailed the intersection of net and the intersection of eye and the intersection of net and the intersection of bar and shelf live until flow upstream to have fish enter but deny in sensor at that time. But run an experiment of factory afterwards, install the electromagnetic flowmeter in the small-scale gutter, put goldfishes to observe, the goldfish bores into the electromagnetic flow sensor, the instrument really presents the spike noise. Later, the questioner informed originally, really saw fish’s shadow in discharging the passway, grown up as becoming the fish after the net bar is bored and entered and discharges the pipeline by the fry.
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