Advanced Diagnosis and Analysis of Four Common Types of Instrument Failures

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Today, building on yesterday’s article, the editor will introduce to you an advanced guide to the diagnosis and analysis of the four most common types of instrument failures; it goes a step further than yesterday’s content, in the hope of being helpful to you. Well, let’s get to the point. Diagnosis and analysis of four common types of instrument failures. First, the steps for analyzing faults in temperature control instrument systems. When analyzing such faults, two things need to be taken into account first: the instruments in this system are mostly electric ones that are used for measurement, indication, and control ； The measurements taken by the instruments in this system are often significantly delayed. 1. If the reading of the temperature instrument system suddenly reaches the maximum or minimum value, it is generally due to a fault in the instrument system. Because the temperature instrument system has a large measurement lag, no sudden changes occur. At this time, the causes of failure are usually broken thermocouples, thermal resistors, compensation wires, or a malfunctioning transmitter amplifier. 2. Rapid oscillations in the indications of the temperature control instrument system are usually caused by improper adjustment of the PID control parameters. 3. Significant and slow fluctuations in the readings of the temperature control instrument system are most likely caused by changes in the process operations. If there are no changes in the process operations at that time, it is likely to be a fault within the instrument control system itself. 4. Steps for troubleshooting the temperature control system itself: Check whether the input signal to the control valve is changing; if the input signal does not change, the control valve operates, and it is possible that there is a leak in the diaphragm of the control valve ； Check whether the input signal to the control valve positioner has changed; if the input signal remains unchanged while the output signal does change, there is a fault with the positioner ； Check whether there is a change in the input signal to the locator, and then check if there is a change in the output of the regulator. If the input to the regulator remains unchanged while its output changes, then it is a fault with the regulator itself. Next, let’s discuss the steps for analyzing faults in pressure control instrument systems. 1. When there is rapid oscillation in the readings of the instruments in the pressure control system, first check whether there have been any changes in the process operations; such changes are usually caused by issues with the process operations or by improper setting of the PID parameters of the regulators. 2. If the instruments in the pressure control system show no response, and the pressure reading remains unchanged despite changes in process operations, the fault is usually located in the pressure measurement system. First, check whether there is any blockage in the pressure sensing conduit system; if not, then examine whether there are any changes in the output of the pressure transmitter. If there are such changes, the fault lies in the controller’s measurement and indication system. Next are the steps for analyzing faults in the flow control instrument system: 1. When the indication value of the flow control instrument system reaches its minimum, first check the field measurement instruments; if they are functioning properly, then the fault lies with the display instrument. When the reading of the on-site measuring instrument is also at its minimum, check the opening degree of the control valve; if the opening degree is zero, it is usually due to a fault somewhere between the control valve and the regulator. When the readings from the on-site measuring instruments indicate a minimum value and the opening degree of the control valve is normal, the possible causes of the fault are insufficient system pressure, blockages in the system pipelines, the pump not being able to deliver sufficient flow, crystallization of the medium, or improper operation. If it is a problem with the instruments, the possible causes include: the orifice plate differential pressure flow meter may have a clogged positive pressure pressure lead ； Leak in the positive pressure chamber of the differential pressure transmitter ； Mechanical flow meters suffer from issues such as gear jamming or clogged filters. 2. When the indication value of the flow control instrument system reaches its maximum, the measuring instrument also often indicates a maximum value. At this point, the control valve can be manually adjusted to open wider or narrower; if the flow rate can be reduced, it is generally due to process operation issues. If the flow rate cannot be reduced, it is caused by issues with the instrumentation system; check whether the control valves in the flow control instrumentation system are functioning properly ； Check whether the instrument’s pressure measurement system is functioning properly ； Check whether the instrument signal transmission system is functioning properly. 3. If the indication values of the flow control instrument system fluctuate frequently, the control can be switched to manual mode. If the fluctuations decrease, it is due to issues with the instruments or inappropriate PID control parameters; if the fluctuations remain frequent, it is caused by problems in the process operation. The last one is the fault analysis procedure for the level control instrument system: 1. When the indication value of the level control instrument system reaches its maximum or minimum value, it is possible to first check whether the sensing instrument is functioning properly. If its indication is normal, switch the level control to manual remote control and observe how the level changes. If the liquid level can be maintained within a certain range, then the fault lies in the liquid level control system ； If the liquid level cannot be stabilized, it is usually due to a fault in the process system, and the cause should be sought from a process perspective. 2. When the indication of the differential pressure type level control instrument does not match that of the on-site direct-reading indicator, first check whether the on-site direct-reading indicator is functioning properly; if its indication is normal, then check for any leaks in the sealing fluid of the negative pressure pressure transfer tube of the differential pressure type level instrument ； If there is a leak, refill the liquid and zero the scale ； There is no leakage; it is likely that the negative migration value of the gauge is incorrect. Adjust the migration value again to make the gauge indicate properly. 3. When the indication values of the liquid level control instrument system fluctuate frequently, it is necessary to first analyze the capacity of the liquid level control object in order to determine the cause of the fault; a large capacity usually indicates that the problem is caused by an instrument failure. For those with low capacity, it is first necessary to analyze whether there have been any changes in the process operations; if so, it is likely that the frequent fluctuations are caused by the process itself. If there is no change, it may be caused by a malfunction in the instrument.