How To Judge The Instrument Failure

The instrument is used to detect, measure, observe, calculate various physical quantities, material components, physical parameters, etc. Instruments, equipment, pressure gauges, length measuring instruments, microscopes, multipliers, etc. belong to the instrument. In a broad sense, the instrument can also have functions such as automatic control, alarm, signal transmission and data processing, such as pneumatic regulating instruments and electric regulating instruments used in automatic control of industrial production processes, and distributed instrument control systems.
1.Visual Inspection
Visual inspection must be very careful. Only gently sway when inspecting components and wiring, do not use excessive force to prevent breakage of components, wiring and printed circuit board copper foil. Do not leave the power switch when the power is turned on. If it is abnormal, it should be turned off in time. Pay special attention to personal safety and absolutely avoid touching both hands with live equipment. The large-capacity filter capacitor in the power circuit has a charging charge in the circuit to prevent electric shock.
2. Investigation Method
The use of investigation methods to repair faults, in-depth and careful, especially for the reflection of the use of on-site personnel to verify, do not rush to open the overhaul. Maintenance experience shows that many of the respondents' responses are incorrect or incomplete, and many problems that require no maintenance can be found through verification.
3. Open Circuit Method
The open circuit method is especially convenient for unitized, combined, and plug-in instrumentation fault detection, and is also effective for some short-circuit faults with excessive current. However, it is not suitable to use a closed system loop or a direct coupled circuit structure in which the overall circuit is a large loop.
4. Short Circuit Method
The short-circuit method is also commonly used to check whether the components are normal. For example, the base and emitter of the crystal triode are short-circuited with tweezers, and the change of the collector voltage is observed to determine whether the tube has amplification. In the TTL digital integrated circuit, the short circuit method is used to judge whether the gate circuit and the trigger can work normally, and the thyristor control electrode and the cathode are short-circuited to judge whether the thyristor is invalid, etc., and some instruments (such as electronic potential difference) can also be used. Count) The input is short-circuited, and the meter indicates the change to determine if the meter is disturbed.
5. Replacement Method
A method of determining the fault at a certain location by replacing certain components or boards.
6. Divisional Law
The branch inspection checks and analyzes the various parts of the instrument and the instrument in order. Although it is more organized, the inspection time is long. In the inspection, the key points are often not caught and a lot of time is wasted. This method is suitable for the maintenance personnel with less maintenance experience, less familiar with the instrumentation fault phenomenon, and the fault is more complicated.
7. Human Body Interference Method
Use the human body interference method to pay attention to the environment. If the electrical equipment and lines are relatively small and the basement and part of the steel building are small, 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 large interference signal. In addition, this method is used to check the high-voltage parts of the instrument or the instruments and instruments that are charged on the bottom plate. Be careful to ensure safety and avoid electric shock.
8. Voltage Method
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. Some faults, such as component short circuit, smoke, flashover, etc., must be turned off, the voltage method will not work at this time, then other methods must be used to check.
9. Current Method
The current method is more troublesome than the voltage method. Generally, the circuit needs to be disconnected and then connected to the ammeter for testing. But it is easier to fail in some cases than the voltage method. The current method and the voltage method cooperate with each other to check and judge most of the faults in the circuit.
10. Resistance Method
The resistance check method is to check whether the input and output resistance of the instrument circuit and part of the circuit are normal with a multimeter under the condition of no power supply; whether the resistance elements are open circuit, short circuit, or whether the resistance value changes; whether the capacitor is broken down or Leakage; inductance coil, transformer with or without wire breakage, short circuit; semiconductor device forward and reverse resistance.