Method for early diagnosis of load cell "sub-health"-2

2. Principles and phenomena
The load cell involves disciplines such as mechanics, electricity, and chemistry. The cause of the fault is complicated and it is difficult to judge. Formation in failure
It is indeed not easy to diagnose in advance that the load cell is in a "sub-healthy" condition.
The faults of the load cell can be divided into three categories according to the principle: A, caused by elastic body; B, caused by electric shock and circuit
的; C, caused by the pasting process. But no matter what kind of failures will be reflected through the unbalanced output.
The size of the zero point output of the load cell is a reflection of the quality of the production process and the quality of the design, and it is also a potential failure
One of the most obvious manifestations.
The zero point output of the load cell is too large, which poses a potential danger to the reliability of the sensor. The change of zero point will also make
The stability of the sensor is not guaranteed. It is found that the zero point is too large during use, which must be caused by a malfunction. The long-term stability of the zero point of the load cell is a prerequisite technical index in the reliability and stability of the sensor. These are the conclusive understandings of the failure of the load cell during many years of work. On this basis, after exploration, it is found that the empty scale output and no-load output signal changes of the load cell. Using monitoring, tracking, and analysis methods, it is possible to grasp the pulse of the “health” of the load cell, from the “change amount”. "Early and accurate diagnosis of the "health" condition of the sensor. At the same time, it also explains the output of the empty scale. The change of the output of the empty scale is a concentrated reflection of two important technical indicators of the load cell zero point and linearity.
The load cell is in the "sub-healthy" condition. The two most common and most sensitive phenomena are the two most common and sensitive characteristics: one is that the weighing indicator often changes zero during use, but it can automatically return to zero without affecting the weighing. The second is that when the standard weight is loaded during the use period, there is often a slight over-tolerance, but it can be restored to normal by adjusting the potentiometer. One of these phenomena indicates that there are "sub-healthy" sensors in the scale. How to find and diagnose?
1. Monitoring
(1) Monitoring of empty scales with load cells. Under actual weighing conditions, the load-bearing device weighs the body (or load-bearing weighing
The frame) is in place, and the mechanical parts are in place. Measure the output value of each sensor of the scale under the excitation voltage, and edit it by position
Good number, make a good record. This is the output value of the sensor's empty scale.
(2) No-load monitoring of the load cell. Under actual weighing conditions, place each sensor of the scale
No-load state, measure the output value of each sensor under the excitation voltage, code the number according to the position, and make a record. This is the transmission
No-load output value of the sensor. At the same time, the input impedance of the sensor is measured, and the output impedance and the no-load output are compared with the technical specifications given by the manufacturer at the factory.
(3) After loading and calibrating the scale with the standard weight, it is best to measure each of the scales under the condition of standard weight loading.
Only the output value of the sensor, number it according to the position, make a record and indicate the standard weight value. This is the sensor's standard weight output
value.
2. Tracking
Determine the time gap of the next measurement according to the place of use, occasion, environment and other conditions. For each sensor
The empty scale output (or standard weight output), no-load output for tracking measurement.
(1) Use the production gap to regularly measure the empty scale output and no-load output of each sensor of the scale.
The conditions can measure the standard weight output of each sensor under the same standard weight. Make a record and compare it with the original record.
(2) When the sensor's empty scale output (or standard weight output) and no-load output change greatly, the tracking time gap should be
Shorten, the tracking density should be increased; when the output is stable for a long time, the tracking gap can be appropriately extended.
(3) The same load is compared by itself at different points (sections) of the scale, and the tolerance is exceeded, and the empty scale of each sensor is measured
Output, no-load output, make a record, and compare with the original record.
This method is commonly used under fast-paced weighing conditions to understand the operating status of the scale.
(4) When the sensor's "sub-healthy" phenomenon appears, it is necessary to increase the output of the empty scale tracking each sensor (or
Standard weight output) The measured density of no-load output, make a record, and compare it with the original record.
(5) For digital sensors, use the same method to enter the empty scale internal code value, empty internal code value, and standard weight internal code value.
Conduct monitoring and tracking, and make good records.
3. Analysis and diagnosis
According to the comparison, it is necessary to carefully analyze the weighing conditions to eliminate falsehoods and seek truth. Targeted on the status of on-site mechanical components
(Pad bumps, etc.) Check to determine whether it is a mechanical problem or other problems. It is a mechanical problem that needs to be corrected and resolved in time. Pass on
Sensory "sub-health" is often accompanied by certain phenomena. The data obtained at this time should be grasped as the analysis section.
Points, discover, confirm and find out the inherent laws in the comparison. After multiple verifications, a diagnostic index is formed to guide today’s
After maintenance work. The type of each sensor and the weighing conditions are different, and the indicators of the "sub-health" status reflected are also different.
For example: after a period of monitoring and tracking analysis of a billet roller table scale, we have a preliminary understanding of the "sub-health" of its sensors
Condition indicator: When the change value of the sensor's empty scale output reaches about 50% to 70% of the mv value corresponding to the sensor's excitation voltage value, the performance of the sensor begins to deteriorate, and it can be diagnosed that the sensor is in a "sub-healthy" condition .
Four, concluding remarks
This method is suitable for resistance strain sensors and digital sensors. Through this method, it is convenient to grasp the time gap of
the sensor from "sub-health" to failure under the actual weighing cond