There are ten methods for fault diagnosis of instrumentation: 1. Observation method Use sight, smell and touch. Sometimes, the damaged components will change color, blisters or burnt spots; burnt-out devices will produce some special odor; short-circuited chips will be hot; the virtual soldering or desoldering can be observed with the naked eye . 2. Percussion hand pressure method Frequently encountered the phenomenon of good and bad when the instrument is running, most of this phenomenon is caused by poor contact or virtual welding. For this situation, tapping and hand pressing can be used. The so-called "knock" is to lightly tap the plug-in board or component with a small rubber head or other knocking objects on the parts that may cause a failure to see whether it will cause an error or a shutdown failure. The so-called "hand pressure" means that when the fault occurs, turn off the power and re-insert the inserted parts, plugs and seats by hand, and then try to turn on the power to eliminate the fault. If you find that tapping the case is normal, and then tapping is not normal, it is best to reinsert all the connectors firmly and try again. If you are unsuccessful, you have to find another way. 3. Exclusion method The so-called elimination method is to judge the cause of the fault by plugging and unplugging some plug-in boards and devices in the machine. When the instrument returns to normal after removing a certain plug-in board or device, it means that the fault is there. 4. Replacement method Two instruments of the same model or sufficient spare parts are required. Replace a good spare with the same component on the faulty machine to see if the fault is eliminated. 5. Comparison method Two instruments of the same model are required, and one is operating normally. To use this method, you must have the necessary equipment, for example, multimeter, oscilloscope, etc. According to the nature of comparison, there are voltage comparison, waveform comparison, static impedance comparison, output result comparison, and current comparison. The specific method is: let the faulty instrument and the normal instrument operate under the same condition, and then detect the signals of some points and compare the two sets of signals measured. If there are differences, you can conclude that the fault is here. This method requires maintenance personnel to have considerable knowledge and skills. 6. Temperature rise and fall method Sometimes, when the instrument works for a long time, or when the working environment temperature is high in summer, a fault occurs. The shutdown check is normal, and it is normal to shut down for a while and then turn on again. After a while, the fault occurs. This phenomenon is caused by the poor performance of individual ICs or components, and the high temperature characteristic parameters fail to meet the specifications. In order to find out the cause of the failure, the temperature rise and fall method can be used. Vortex flowmeter The so-called cooling is to use cotton fiber to wipe the anhydrous alcohol on the parts where the failure may occur, so as to cool the temperature, and observe whether the failure is eliminated. The so-called warming is to artificially raise the ambient temperature. For example, use an electric soldering iron to place the suspected part (be careful not to raise the temperature too high to damage the normal device) to see if the fault occurs. 7, riding shoulder method The riding method is also called parallel method. Install a good IC chip on the chip to be inspected, or connect good components (resistance, capacitance, diode, triode, etc.) in parallel with the component to be inspected to maintain good contact. If the fault is caused by an open circuit inside the device or Reasons such as poor contact can be eliminated by this method. 8. Capacitor bypass method When a circuit has a strange phenomenon, such as a disordered display, you can use the capacitor bypass method to determine the part of the circuit that is probably malfunctioning. Connect the capacitor across the power and ground terminals of the IC; connect the transistor circuit across the base input or collector output, and observe the impact on the fault phenomenon. If the bypass input terminal of the capacitor is invalid and the fault phenomenon disappears when bypassing its output terminal, it is determined that the fault appears in this stage of the circuit. 9. State adjustment method In general, before the fault is determined, do not touch the components in the circuit, especially the adjustable devices, such as potentiometers. However, if multiple reference measures are taken in advance (for example, position marks or voltage or resistance values ​​are measured before being touched), touch is allowed if necessary. Maybe after the change, sometimes the fault will be eliminated. 10. Quarantine The fault isolation method does not require comparison of equipment or spare parts of the same model, and is safe and reliable. According to the fault detection flowchart, segmentation and envelopment gradually narrow the fault search range, and then cooperate with signal comparison, component exchange and other methods, the fault will generally be quickly found.
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Failure analysis and solutions of instrumentation