Instrument failure is a problem that we often encounter in our work, so what are the good ways to judge the failure and find out the problem? The following editors have sorted out 10 methods for analyzing and judging industrial instrument faults for you, summarizing years of instrument maintenance experience, and hoping to be helpful to you.
1
visual inspection
A method to observe and find faults through human senses (eyes, ears, nose, hands) without any testing equipment. The visual inspection method is divided into two types: visual inspection and startup inspection.
The visual inspection mainly includes:
â‘ Whether the instrument shell and dial glass are in good condition, whether the pointer is deformed or colliding with the dial, whether the assembly fasteners are firm, whether the position of each switch knob is correct, whether the movable part rotates flexibly, and whether there is any obvious change in the adjustment part;
â‘¡ Whether the connection is disconnected, whether the connectors are normally connected, whether the reeds on the circuit board socket are insufficiently elastic and have poor contact. For the instrument assembled by unit combination, special attention should be paid to whether the connecting screws of each unit board are tightened;
â‘¢ Whether the contacts of each relay and contactor are dislocated, stuck, oxidized, scorched and stuck to death, etc.;
â‘£Whether the power fuse is blown, whether the electronic tube is broken, leaking (a layer of white powder is attached to the inner wall of the tube after the leak), damaged, whether the paint of the transistor shell is discolored, broken, whether the resistance is burnt, whether the coil is broken, whether the capacitor Whether the shell is swollen, leaking or bursting;
⑤ Whether the copper-clad strip of the printed board is broken, tinned, or short-circuited, whether the solder joints of each component are in good condition, and whether there is a phenomenon of virtual soldering, missing soldering, and desoldering;
â‘¥ Check whether the arrangement and wiring of the components are skewed, dislocated, dropped or collided.
The start-up inspection mainly includes:
â‘ Whether the power indicator light, each electronic tube and other light-emitting elements in the machine are energized and illuminated;
â‘¡Whether there is high voltage ignition, discharge and smoke in the machine;
â‘¢Whether there is vibration and crackling, friction and impact sound;
â‘£ Whether the temperature rise of transformers, motors, power amplifier tubes and other heat-prone components, resistors, and integrated blocks is normal, and whether there is any hot hand phenomenon;
⑤ Is there any special smell in the machine, such as the burnt smell caused by the burning of the insulating layer of the transformer resistance, and the free oxygen smell caused by the ionization of the air caused by the high-voltage leakage of the oscilloscope tube;
â‘¥ Whether the mechanical transmission part is running normally, whether there are bad gear meshing, stuck and serious wear, slip deformation, transmission failure and so on.
Visual inspection must be very careful and careful, and should not be careless and impatient. When checking the components and connections, you can only shake them gently, and do not use too much force to prevent breaking the components, connections and the copper foil of the printed board. Do not leave the power switch with your hands when turning on the power and check the power. If any abnormality is found, it should be turned off in time. Pay special attention to personal safety and absolutely avoid touching live equipment with both hands at the same time. The large-capacity filter capacitors in the power supply circuit are charged in the circuit to prevent electric shock.
twenty two
Survey
Through the investigation and understanding of the failure phenomenon and its production and development process, the method of judging the cause of the failure is analyzed. Generally there are the following aspects:
â‘ The usage before the failure and whether there are any signs;
â‘¡Whether there is fire, smoke, abnormal smell, etc. when the fault occurs;
â‘¢ Changes in power supply voltage;
â‘£Overheating, lightning, humidity, collision and other external conditions;
⑤ Whether it is disturbed by external strong electric field and magnetic field;
â‘¥Whether there is improper use or misoperation;
⑦The fault that occurs under normal use, or the fault that occurs after repairing and replacing components;
⑧ What failures and repairs have occurred in the past.
Use the investigation method to repair the fault, the investigation and understanding should be in-depth and careful, especially the feedback of the on-site users should be verified, and do not rush to disassemble and repair. Maintenance experience shows that many of the user's reflections are incorrect or incomplete, and many problems that do not require maintenance can be found through verification.
3
circuit breaker
Disconnect the suspected part from the whole machine or unit circuit to see if the fault disappears, so as to determine the method of the fault.
After the instrument fails, first determine several possibilities of the failure. In the fault range area, disconnect the suspected part of the circuit to determine whether the fault occurs before or after the disconnection. If the power-on inspection finds that the fault disappears, it indicates that the fault is mostly in the disconnected circuit. If the fault still exists, do further open circuit segmentation inspection, gradually eliminate the suspicion, narrow the scope of the fault, until the real cause of the fault is found.
The open-circuit method is particularly convenient for the fault inspection of unitized, combined and plug-in instruments, and is also effective for some short-circuit faults with excessive current. However, it is not suitable for closed system loop or direct coupled circuit structure where the overall circuit is a large loop.
4
short circuit method
A method of temporarily short-circuiting a certain level of circuit or component that is suspected to be faulty, and observing whether the fault status changes to determine the fault location.
When the short-circuit method is used to check multi-level circuits, after a circuit or component of a certain level is temporarily short-circuited, if the fault disappears or decreases significantly, it means that the fault is before the short-circuit point, and the fault is after the short-circuit point if there is no change. If the potential of the output terminal of a certain stage is abnormal, the input terminal of the stage is short-circuited. If the potential of the output terminal is normal at this time, the circuit of this stage is normal.
The short-circuit method is also often used to check whether the components are normal. For example, short-circuit the base and emitter of the transistor with tweezers, observe the change of the collector voltage, and determine whether the tube has amplifying effect. In the TTL digital integrated circuit, the short circuit method is used to judge whether the gate circuit and the flip-flop can work normally. Short-circuit the control electrode and cathode of the thyristor to determine whether the thyristor fails, etc. In addition, the input terminals of some instruments (such as electronic potentiometers) can also be short-circuited, and the instrument can be judged whether it is disturbed by the change of the indication of the instrument.
5
substitution method
By replacing certain components or circuit boards to determine the method of failure in a certain part.
Replace the suspected components with components with the same specifications and good performance, and then power on the test. If the fault disappears, it can be determined that the suspected component is the fault. If the fault still exists, the same substitution test can be performed on another suspected component or circuit board until the fault location is determined.
Before replacing, take a little time to analyze the cause of the failure, instead of blindly replacing components. If the failure is due to a short circuit or thermal damage, a good replacement component may also be damaged. Another example is that a diode is burnt out, which may be due to insufficient working current and reverse peak voltage of the tube. If another diode of the same type is replaced at this time, the fault will only be temporarily dealt with, but not eradicated.
In addition, the replacement of components should cut off the power supply, and it is not allowed to test while welding while electrified. When the replaced components are installed and welded, they should comply with the original welding installation method and requirements. For example, there is generally an insulating sheet between the high-power transistor and the heat sink, and do not forget to install it. When replacing, be careful not to damage other components around, so as not to cause human failure.
6
Division method
In the process of finding faults, a method of dividing the circuit and electrical parts into several parts to find out the cause of the fault.
The general detection and control instrument circuit can be divided into three parts, namely the external circuit (the whole circuit from the terminal of the instrument to the detection element and the control actuator), the power circuit (the whole circuit from the AC power supply to the power transformer, etc.), the internal circuit Circuits (all circuits except external circuits and power circuits). In the internal circuit, it can be divided into several small parts (according to the characteristics of its internal circuit and the structure of electrical components). Partial inspection is to inspect each part from the outside to the inside, from the big to the small, and from the outside to the inside according to the divided parts, and gradually narrow the scope of suspicion. When the inspection determines which part of the fault is, then do a comprehensive inspection of this part to find the fault location.
The branch inspection is to inspect, analyze and judge the various parts of the instrument in order. Although it is more organized, the maintenance time is long, and the key points are often not grasped during the inspection, which wastes a lot of time. This method is suitable for maintenance personnel with less maintenance experience, less familiarity with instrumentation failure phenomena, and more complex failures.
7
human interference
When a person is in a messy electromagnetic field (including the electromagnetic field generated by the AC power grid), a weak low-frequency electromotive force (nearly tens to hundreds of microvolts) will be induced. When the human hand touches some circuits of the instrument, the circuit will reflect. Using this principle, some fault parts of the circuit can be easily judged.
The human interference method should pay attention to the environment in which it is located. For example, there are few electrical equipment and lines, basements, some reinforced buildings, etc., the signal generated by the interference will be smaller. At this time, a long wire can be used instead of the hand to obtain a larger interference signal. In addition, when using this method to check the high-voltage part of the instrument or the instrument with the bottom plate charged, be sure to pay great attention to safety to avoid electric shock.
8
Voltage method
The voltage method is to use a multimeter (or other voltmeter) to measure the suspected part with the appropriate range, and to measure the AC voltage and the DC voltage separately. Measuring AC voltage mainly refers to AC power supply voltage, such as AC 220V network voltage, AC voltage stabilizer output voltage, transformer coil voltage and oscillation voltage, etc.; The voltage of each lead-out corner to ground, etc.
The voltage method is one of the most basic methods in maintenance work, but the range of faults it can solve is still limited. Some faults, such as a slight short circuit of the coil, a broken capacitor or a slight leakage, are often not reflected in the DC voltage. For some faults, such as short circuit of components, smoke, flashover, etc., the power must be turned off. At this time, the voltage method will not work. At this time, other methods must be used to check.
9
current method
The current method is divided into two types: direct measurement and indirect measurement. Direct measurement is to connect the ammeter in series after the circuit is disconnected, and compare the measured current value with the data when the instrument is in normal working state, so as to judge the fault. If it is found that any part of the current is not within the normal range, it can be considered that this part of the circuit has a problem, or at least has been affected. The indirect measurement does not need to disconnect the circuit, the voltage drop on the resistance is measured, and the approximate current value is calculated according to the size of the resistance value, which is mostly used for the measurement of the current of the transistor element.
The current method is more troublesome than the voltage method. Generally, the circuit needs to be disconnected and connected in series with an ammeter for testing. But it is more prone to failure than the voltage method in some occasions. The current method and the voltage method cooperate with each other, which can check and judge most of the faults in the circuit.
10
resistance method
The resistance inspection method is to use a multimeter to check whether the input and output resistance of the whole circuit of the instrument and some circuits are normal; whether the resistance elements are open, short-circuited, and whether the resistance value changes; whether the capacitor is broken down or not. Leakage; whether the inductance coil and transformer are disconnected or short-circuited; the forward and reverse resistance of semiconductor devices; the resistance of the lead pins of each integrated block to the ground; and the β value of the transistor should be roughly judged; whether there is a short circuit between the electron tubes and oscilloscope tubes, and whether the filament is in good condition Wait.
When applying the resistance method to check for faults, the following points should be noted:
â‘ Since there are many nonlinear elements in the circuit, such as transistors, large-capacity electrolytic capacitors, etc., when the resistance method is used to measure the resistance between two points, these nonlinear elements are connected, so pay attention to the red and black poles of the multimeter. sex, because the results measured by different polarities are different;
② Avoid using Ω×1 block (higher current) and Ω×10K block (higher voltage) to directly measure transistors and integrated circuits with low current and low withstand voltage to avoid damage;
â‘¢ Most of the components under test in the instrumentation are involved (series or parallel) many other components on the circuit. Therefore, for the occasions where there is no direct breakdown but leakage or the resistance value is relatively large, the inspection and measurement should be carried out after the component under test is disconnected. For components such as resistors and capacitors with only two lead wires, just disconnect one lead wire, and for components with three wires such as transistors, etc., two lead wires should be disconnected.
FBT WDM - Fused Biconic Taper Wavelength Division Multiplex
A fusion taper type wavelength division multiplexer, comprising an input end cone, an output end cone, and a coupling area. The input end cone is located at one end of the coupling area, and the output end cone is located at the coupling area. At the other end of the zone, the input end cone includes an input arm and a backscatter arm, the output end cone includes a through arm and a coupling arm, and the optical power is input from the input arm of the input end cone through the The coupling zone is redistributed after coupling and output from the output end cone. A part of the optical power is output from the through arm and the other part is output from the coupling arm. The coupling zone includes two optical fibers, and the cladding parts of the two optical fibers are mutually connected. Close, when pulling the taper, the two optical fibers are pulled in opposite directions but cannot move relative to each other. The two optical fibers are processed by a fusion taper device.
At present, the method of making FBT WDM in industry is to use a flame to heat and melt the fiber at a single point and then stretch it. The defect is that the heating area is too short, resulting in a short stretchable length (corresponding to the coupling length), and the fiber diameter is not small enough, so This limits the minimum channel spacing that this type of wavelength division multiplexer can achieve.
FBT WDM, also known as Fused Biconic Taper WDM and FBT WDM Splitter, along with LAN WDM Splitter, Filter WDM splitter, dense WDM splitter and coarse WDM splitter, are the most commonly used WDM device in construction of PON.
Further, the melting taper device is formed by two insulation bricks made of aluminum oxide fiber insulation material to form a cavity, and the high temperature heat source is provided by an electric heating wire made of molybdenum disilicide material, and the heating wire is located In the heating tank, the heating temperature is adjusted by adjusting the voltage at both ends of the electrodes connected to it, the optical fiber passes over the heating wire, and the taper speed is adjusted by changing the rotation speed of the programmable stepping motor driver.
Further, the two optical fibers are fused and tapered in the fusion tapering device, one of which is used as the input power of the input arm, and the other is used as the coupling arm fiber. After the tapering length reaches a certain distance, the two fibers are coupled, and the optical power is Continuously couple into the coupling arm fiber, continue to taper, and the optical power is repeatedly and alternately coupled in the two fibers.
FBT WDM, Fused Biconic Taper WDM, FBT WDM Splitter
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