10 Kinds of Inspection Methods For The Failure of Weighing Instrument

This paper introduces the application of ten methods, such as comparison method, plug and pull method, trial method, etc., to quickly check the various fault causes of changzhou tolituo 8142 series weighing instruments, and illustrates them with examples.

The three parts of the electronic weighing device are composed of a scale platform, a sensor and a weighing instrument. The function of the weighing instrument is to measure the weight of the heavy objects on the scale platform through the change of the measuring sensor and give instructions in digital form.8142-07, 8142-08, 8142 PRO meter is a company's large usage, the application of a wide range of products, the meter has high sensitivity, high resolution, rich software functions,In more than one hundred truck scales in Hefei, 50% of them use this kind of instrument. Here, I introduce several ways to find the reasons for the failure of 8142 weighing instrument based on my years of working experience.

1. The fault observation method is to look for abnormal conditions of parts by naked eye observation, such as welding, welding, wire break, misassembly, burning, discoloration, short circuit, touch sundry and so on.For example, the reading of one instrument is unstable and inaccurate. When the instrument is checked with the simulator, it is found to be normal, and then the scale body is checked. When the junction box is found to be seriously damp, it is removed, swabbed and dried with alcohol, and then connected to normal.If there is an instrument display value at the end of the jump in 3 numbers, inspection found that the instrument and sensor interface J3 9th needle to the outside of the curved Angle caused by bad grounding, straighten, show stability;For example, there is an instrument boot self-test before the fuse is blown, open the front cover to take out the circuit board Q8(LM340J-15) back coke yellow, check the connection with the capacitor C48, found to have been broken down, replacement, display normal.

2. Plugging method, is to pull out a component or plug in the analog component again, to see where the fault is.For example, if the display reading of an instrument is unstable, unplug the connecting cable from the junction box to the display instrument and connect the simulator. If the reading of the instrument is stable at this time, it indicates that the problem lies with the sensor or junction box, not the instrument; otherwise, it indicates that the problem lies with the instrument.In addition, the display reading does not return to zero, unplug the junction box to the display instrument connection cable, check the instrument set F4.1 and so on are normal, then the cause of the fault in the sensor scale body, can check whether the sensor limit clearance is too large, whether there is a foreign body beside the connector debris, whether there is a brick under the scale body to prevent the scale body reset.

3. The trial fault method is to replace the parts with normal parts with suspected faults, also known as the substitution method. This method should be easy but difficult.For example, a meter can not self-check, suspected A4(27256EPROM) and A10(X2210) has a problem, replace the normal A4(with a program) after troubleshooting;Another example is that some of the keys in the instrument do not work when pressed, and the original keys that do not work when replaced by a new keyboard still do not work. After checking the socket, it is found that one foot is welded, and troubleshooting after repair welding.

4. Comparison method is to compare the correct features (waveform, voltage) with the wrong features to find the fault. This requires the maintainer to be familiar with the circuit diagram and understand the voltage and waveform of the main test points.For example, the display reading of one meter keeps turning over, check the excitation voltage (A29 6 pin) is 21V, which is on the high side, and A29(LT1021-10) is suspected to be bad. After replacing the normal A29, the excitation voltage is restored to 12.5V, indicating normal;If there is an instrument self-test display "", inspection found that Q10C foot resistance to the ground increases, R74(56KΩ) open circuit, put on a new resistance, display back to normal.

5. The measurement method is to measure the level of each point of the instrument in a specific state with a multimeter, and then analyze and judge the cause of the fault according to the logic principle.For example, if the keys of A certain instrument keyboard fail to respond, if the panel keyboard is replaced with normal keyboard, the fault still exists. If A9(8741) and A7(8243) are replaced, the fault still exists. If A, B,CC1,2,3 pins) is low level Y0(pin 15) still does not turn over, after replacing A11 troubleshooting;For another example, if some parameters of a meter cannot be set, check the potential of each pin A2(74LS373), and the level of pin 9 is abnormally high. If A2 is changed, the meter can be set normally.

6. Principle method, is based on the working principle of electronic weighing instrument, from the principle of analysis to find the cause of the fault method.For example, the error code indicates that the elimination method has an instrument reading is not stable, but it is not a random jump, so it can eliminate the problem of the digital logic circuit, check the output voltage of the sensor, and find that the voltage is on the high side, so it can be inferred that the excitation voltage is on the high side, and the Q7C foot is 19V.According to the schematic diagram analysis, Q7 and A29 output in parallel, while Q7 works in the constant current mode, so the voltage instability is mainly caused by the problem of A29(LT102E), which is responsible for voltage stabilization, and the fault disappears when replacing A29.As another example, one meter, press the PRINT key can't PRINT, after using heuristics in a keyboard, press the PRINT key can PRINT, after point out on the keyboard, according to the principle diagram, the keyboard is measured with a multimeter to elicit resistance between cable 7 feet and 9 feet, not on time for open circuit, when press the normal for 32 k should be 38 Ω, illustrates the key contact undesirable.

7. The temperature rise method is to raise the ambient temperature or local temperature in a human way, so that the poor quality wafer is exposed to help find the fault method.Occasionally, the meter will fail after a long period of operation or when the ambient temperature rises. This is mainly due to the poor quality of a component.For example, after an instrument works for a period of time, the display accuracy becomes worse, the instrument current is cut off, and the internal temperature of the instrument drops, and then the power is connected. At this time, the fault has not yet appeared, and the electric iron is used to bake A28(7652), and then bake A27(7652) to appear digital turnover, A27 fault elimination, it is worth noting that the temperature can not rise too high, so as not to damage the components.

8. Knocking method is to use a small rubber hammer or finger to gently knock some parts of the instrument when checking the comparison method, trial method, etc., so that the abnormal situation can be reproduced and find out the fault method. If the instrument has false welding or poor contact, the contact resistance of the metallization hole increases, the method can be used to check the knock method.For example, there is an instrument that shows the end of the flip, knock the shell by hand, the flip phenomenon will reappear, after inspection found that the nut on the grounding bolt is loose, tight, fault elimination;Another example is that there is a phenomenon that an instrument is printed when it is not printed. After a while of knocking, it can sometimes continue to print. It is found that the cable connecting the instrument to the printer is close to the printer plug, and a wire is disconnected.

9. Segmentation method is to divide the fault range from components to a certain line or point on the circuit board to find the fault location of weighing instrument one by one.For example, there is a meter a power on that is to burn the fuse, touch it by hand, found that Q8(LM304T-15) is very hot, with a multimeter Q8 output short circuit, welding Q8 and then test the circuit board, still short circuit, cut the copper foil leading to A27(7652), still short circuit test, then cut A28(At this time, only C39 is actually connected to the two ends of 15V. Under welding C39, the output of Q8 is no longer short-circuited, and the fault is removed after replacing C39.

10. Code diagnosis method, is to use the instrument automatic diagnosis display error code code to find the fault method.

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