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Ten methods for diagnosing faults in chemical process instruments; Ten methods for identifying faults: 01. Investigation method. By investigating the fault symptoms and their development process, the cause of the fault is analyzed and determined. 02 Visual inspection method. Without any testing instruments, faults are detected by using human senses (eyes, ears, nose, hands). 03 Circuit-breaking method. Disconnect the suspected part from the entire device or the individual circuit to see if the fault disappears, thereby determining where the fault lies. 04 Short-circuit method. Temporarily short-circuit the circuit stage or component suspected to be faulty, and observe whether there is any change in the fault condition in order to determine the location of the fault. 05 Replacement method. By replacing certain components or circuit boards, it is possible to determine where the fault lies. 06 Division method. During the process of troubleshooting, the circuit and electrical components are divided into several sections to identify the cause of the fault. 07 Human interference method. When in a chaotic electromagnetic field (including those generated by AC power grids), a weak low-frequency electromotive force is induced (ranging from several tens to several hundred microvolts). When a person touches certain circuits of the instruments, those circuits respond, and this principle can be used to simply identify the faulty parts in the circuits. 08 Voltage method. The voltage method involves using a multimeter (or other voltage meter) with an appropriate range to measure the suspected part, with measurements taken for both AC voltage and DC voltage. 09 Current method. The current method is divided into direct measurement and indirect measurement. Direct measurement involves disconnecting the circuit and connecting an ammeter in series to measure the current value; by comparing this value with the one obtained when the instrument is in normal operation, a fault can be identified. Indirect measurement involves keeping the circuit closed, measuring the voltage drop across the resistor, and calculating an approximate current value based on the resistance value; it is often used for measuring the current in transistor components. 10 Resistance method. The resistance check method involves using the resistance setting on a multimeter, without powering the device, to verify whether the input and output resistances of the entire circuit as well as certain sub-circuits of the instrument are normal, whether capacitors have blown or are leaking current, and whether inductors and transformers have any breaks or short circuits.