Instrument failure is a common problem that we encounter in our work. So, what are the good methods for identifying faults and identifying problems? Below, Baijian Testing has compiled 10 methods for analyzing and judging industrial instrument faults, summarizing years of experience in instrument maintenance, hoping to be helpful to everyone

First, visual inspection method

The method of observing and discovering faults through human senses (eyes, ears, nose, hands) without any testing equipment.

. There are two types of visual inspection methods: appearance inspection and startup inspection

1. Appearance inspection mainly includes:

Whether the instrument casing and dial glass are intact, whether the pointer is deformed or collides with the dial, whether the assembly fasteners are firm, whether the positions of each switch knob are correct, whether the movable parts rotate flexibly, and whether there are obvious changes in the adjustment parts;

Whether the wiring is disconnected, whether all connectors are connected normally, whether the spring on the circuit board socket is not elastic enough or has poor contact. For instruments assembled with unit combinations, special attention should be paid to whether the connecting screws of each unit board are tightened Check if the contacts of each relay and contactor are misaligned, stuck, oxidized, burnt or stuck Check whether the power fuse is blown, whether the electronic tube is broken, leaking (a layer of white powder adheres to the inner wall of the tube after leakage), damaged, whether the paint on the transistor shell is discolored or broken, whether the resistance is burnt, whether the coil is broken, and whether the capacitor shell is swollen, leaked, or burst Check whether the copper strip on the printed board is broken, soldered, or short circuited, whether the solder joints of each component are in good condition, and whether there are any false soldering, missing soldering, or detachment phenomena Check if the arrangement and wiring of various components are skewed, misaligned, detached, or colliding

2. Startup inspection mainly includes:

Whether the internal power indicator light, electronic tubes, and other light emitting components are powered on and on Is there any phenomenon of high-voltage ignition, discharge, or smoke inside the machine Whether there is vibration and the sound of cracking, friction, and impact is emitted Check whether the temperature rise of easily heating components such as transformers, motors, power amplifier tubes, resistors, and integrated blocks is normal, and whether there is any hot hand phenomenon Is there any special odor inside the machine, such as the burnt smell caused by the insulation layer of the transformer resistor, and the self oxygen odor generated by the high voltage leakage ignition of the oscilloscope tube that ionizes the air Whether the mechanical transmission part operates normally, and whether there are any phenomena such as poor gear meshing, jamming, severe wear, slipping deformation, and ineffective transmission Visual inspection must be very careful and careful, avoiding carelessness and impatience. When checking components and wiring, only gently shake and do not use excessive force to prevent breaking components, wiring, and printed board copper foil. Do not leave the power switch with your hands when turning on and checking the power supply. If any abnormalities are found, turn it off in a timely manner. Pay special attention to personal safety and absolutely avoid both hands coming into contact with live equipment. The large capacity filter capacitor in the power circuit carries a charging charge in the circuit, so it is necessary to prevent electric shock

Secondly, investigation method

By investigating and understanding the fault phenomenon and its development process, analyze and determine the method of fault cause.

. There are generally the following aspects:

The usage situation before the fault occurs and whether there are any signs Is there any phenomenon of ignition, smoke, abnormal odor, etc. when the fault occurs Changes in power supply voltage External conditions such as overheating, lightning, humidity, collisions, etc Whether there is interference from strong external electric and magnetic fields Is there any improper use or misoperation The fault that occurs under normal use or after repairing or replacing components What faults and repair situations have occurred before

Use the investigation method to troubleshoot faults. The investigation should be thorough and careful, especially to verify the feedback of on-site users. Do not rush to disassemble for maintenance. Maintenance experience has shown that many user reactions are incorrect or incomplete, and verification can reveal many issues that do not require maintenance

Thirdly, the circuit breaker method

Disconnect the suspected part from the entire machine or unit circuit, see if the fault can disappear, and then determine the method where the fault is located.

After the instrument malfunctions, first preliminarily determine the several possibilities of the malfunction. Disconnect the suspected part of the circuit within the fault area to determine whether the fault occurred before or after disconnection. If a fault is found to disappear during power on inspection, it indicates that the fault is mostly in the disconnected circuit. If the fault still exists, further open circuit segmentation inspection should be carried out to gradually eliminate suspicion and narrow the fault range until the true cause of the fault is found The circuit breaker method is particularly convenient for detecting faults in modular, modular, and plug-in instruments, and is also effective for some short-circuit faults with excessive current. However, closed system circuits or directly coupled circuit structures with large loops are not suitable for the overall circuit

Fourth, Short Circuit Method

The method of temporarily short circuiting a suspected faulty circuit or component and observing any changes in the fault status to determine the fault location.

When using the short circuit method to check multi-level circuits, if the fault disappears or significantly decreases after a certain level of circuit or component is temporarily short circuited, it indicates that the fault is before the short circuit point, and if there is no change in the fault, it is after the short circuit point. If the output terminal potential of a certain stage is abnormal, short-circuit the input terminal of that stage. If the output terminal potential is normal, then the circuit of that stage is normal Short circuit method is also commonly used to check whether the components are normal, such as using tweezers to short circuit the base and emitter of the crystal transistor, observe the voltage changes of the collector, and determine whether the tube has amplification effect. In TTL digital integrated circuits, the short circuit method is used to determine whether the gate circuit and trigger can work properly. Short circuit the thyristor control electrode and cathode to determine if the thyristor is ineffective. In addition, certain instruments (such as electronic potential difference meters) can also be short-circuited at the input end to determine whether the instrument is affected by interference by observing changes in instrument indications