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The impact sensor combines new measurement methods with conventional 4-20 mA loop-powered sensor technology.

Impact sensor

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Impact sensor powers new measurement method and conventional 4-20 mA loop

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The vibration signal of a rotary compressor has a relatively stable mode, while the vibration signal of a reciprocating machine contains a large number of transient, unstable, and transient impact components. An attempt is made to accurately analyze what mechanism each component corresponds to. Very difficult job. The idea of the impact sensor is whether all these transient, unstable, and transient components can be used to form a new and effective monitoring mode, that is, the method of detecting the steady-state mode by the rotary compressor is no longer used. Instead, it detects the impact caused by the unique reversing motion of the reciprocating machine, and predicts the possible bolt loosening, increased clearance, valve cracks, and many forms of failure that may occur in reciprocating machines through the degree of impact. The assumption is logical: under normal circumstances, a reciprocating machine should have some kind of impact "pattern". This shock mode refers to the magnitude and number of shock events that occur within a given period of time. Deviations from normal conditions, such as loosening of bolts or mating places, cracks inside moving parts, etc., will cause significant changes in the impact mode. The determination of the normal mode is to a certain extent the nature of empirical data, rather than being calculated by theory, but it has proven to be feasible in practice. In this regard, much like the original experience of a skilled technician or worker, tapping with an iron rod, and then listening to the sound inside the machine with the ear to determine the operating state of the machine, the method looks old, but effective. Shock sensors are used to sense high-amplitude, short-term spikes, a feature that characterizes most potential problems in reciprocators. These sharp pulses do not occupy a significant proportion of the total energy of the steady-state vibration signal, and they often do not show up in the traditional signal processing process used to detect rotary compressors. In the impact sensor, a special peak detection circuit captures and calculates the number of times of impact events exceeding the threshold within a specified length of time. This counting method has proven to be very reliable in practice, thus forming the work of the impact sensor principle.

Since the impact sensor is used to identify conditions such as looseness, cracks, breaks, etc., one is arranged on the crosshead slide box shell of the four cylinders of the GB302D reciprocating compressor, and the installation direction is perpendicular to the direction of movement of the connecting rod for measurement. Impact intensity caused by failure of the connecting rod nut, broken connecting rod, etc.

After the sensor is installed and the compressor is working normally, the threshold can be set. It should be noted that the polarity of the power connection of the impact sensor in the test mode and the normal operation mode are exactly the opposite. A 250 resistor is used to convert current pulses into voltage pulses for display on an oscilloscope. Adjustment can also be performed with the help of a hand-held 6850 impact meter, which is connected to the impact sensor via a dedicated socket.

The alarm current value when the impact event exceeds the allowable range can be set according to different applications. For example, the early warning can be set to 8 mA (4 impact events that exceed the threshold), and the emergency alarm can be set to 12 mA (8 events that exceed the threshold Shock event). There is a certain relationship between the threshold value and the alarm current value. If the threshold value is set lower, the alarm current value should be set higher. In order to accumulate operating experience, do not prematurely use the alarm signal and compressor operation to directly adopt mechanical interlocking, but design the alarm form to display the number of impact events that cross the boundary with different colors on the host computer's homepage to attract the attention of staff . In addition, under the trend analysis menu on the compressor parameter analysis page, the historical trend of the characteristic parameters of the four cylinders of the compressor including the number of shocks can be displayed, and the position of the slider below the display area can be changed. Threshold impact times.