Elevator electrical fault finding method

Abstract:When looking for a fault, do not rush to do it, you sho […]

When looking for a fault, do not rush to do it, you should first understand the fault phenomenon. Find the fault point by looking, smelling, asking, and listening. If the elevator equipment (such as machine room equipment) you see has no peculiar smell, you can perform an actual elevator test to find the fault point.
Put the elevator in the inspection state, and operate the elevator car to run slowly with the landing doors and car doors closed. If the elevator can run under the inspection state, it means that the elevator main drive control system, safety circuit, and mechanical system are not faulty, and the fault may be in the electrical control circuit. If there is no maintenance operation, then the safety circuit is short-circuited. If the car can be moved at this time, the failure point is in the safety circuit; if there is still no maintenance operation, the failure point is in the main drive system or mechanical system. During the maintenance operation, it should also be observed whether the electromagnetic brake is normal, and the brake failure is relatively intuitive.
In addition to inspecting the equipment by listening, smelling, touching, and looking for electrical faults, it is also necessary to measure and experiment on the circuit to find the fault point. The following are several commonly used fault detection methods.

⒈ Resistance method.

When the switch contacts are in poor contact or the circuit breaks down, you can use a multimeter to block the measurement. The measurement should be performed when the circuit is powered off. To test whether the switch contacts are in good contact, you can connect the multimeter test leads to both ends of the circuit, and then use a wire to short-circuit both ends of the tested switch contacts. If the multimeter's electrical blocking indicator becomes small or passes, it indicates that the switch is the fault point. When measuring whether a longer wire is broken, you can ground one end of the wire and use a multimeter to measure the resistance of the other end of the wire to ground. If it does not work, it means that the wire has a break.
When measuring, we must also pay attention to selecting the appropriate party committee, otherwise we will draw wrong conclusions. For example, when the two points B and D in the measurement graph are open, low resistance should be selected. At this time, the measured value is zero, indicating that the wire is connected; if there is a resistance whose resistance is the resistance of the K1 and K2 contactor coil, it means Points B and D are unreasonable. If the high barrier is selected for measurement, even though the two points B and D are disconnected, B, A, C, and D also form a loop. The coil resistance is small and the indication of the measurement result is almost close to zero, which is easy to draw wrong conclusions.
When measuring the elevator circuit with a computer that only allows very small current to pass, a high-resistance multimeter should be used instead of a general multimeter R×1 file, because when a general multimeter uses this file to measure low resistance values, there will be 50mA in the loop The passing of ~100mA current can easily cause the electronic components to be burnt out during the measurement process.
Example: There is a lighting lamp, but the bulb does not light up. After checking that the bulb is not broken, the plug is intact, and the lamp holder wiring is not loose, the voltage 36V fully meets the requirements, and the appearance of the power cable is intact. Based on the above situation, it is preliminarily judged that the fault is on the inner core wire of the cable, and there may be a break in the core wire.
Use a multimeter to find the disconnection point, the method is as follows.
⑴Measure the cable resistance. Short-circuit the two wires at the plug and measure the resistance between the screw of the lamp cap and the center piece. If not, the core wire is broken.
⑵ Confirm the disconnection. Connect one test lead to the short-circuiting position of the plug, and the other test lead to overlap the screw port and the center pressure piece in turn.
⑶ Find the disconnection. Insert the needle hole into the wire core at 1/2 of the broken wire, measure the resistance between the needle and the broken wire, and the unconnected end is the fault section.
⑷ At 1/2 of the fault section, insert the needle into the core wire, the probe and the needle, the needle and the resistance of the other end, and the unconnected end is the fault section.
⑸Measure sequentially until the fault point is determined.
The above method is called "optimization method", it can quickly detect the fault point to save the time to find the fault.
It is also very convenient to use the resistance method to find the fault points of the safety circuit and the door interlocking circuit. For example: the door interlocking failure, the interlocking relay does not suck, the elevator will not start running, see the figure.
`The specific method is to use a multimeter to block the resistance of the MSJ coil a and b of the door lock relay (disconnect the power supply voltage). If the resistance meter needle does not move, it means that the coil is broken; if the coil is intact, it means that the fault lies in the interlock switch of each floor. Measure the contacts of each switch on each floor door, and the contact failure is the fault contact.

2. Voltage method.

The voltage measurement method needs to be carried out when there is electricity in the line. Use the DC block to measure the DC voltage and the AC block to measure the alternating current. Note that the line voltage and the multimeter pen are in contact with both ends of the tested contact. If the multimeter has instructions, the contact is not connected. If there is no indication, the contact has been connected. At this time, the possibility that the tested contact gets power from other places should be excluded. To measure the DC voltage of the computer, a multimeter or digital voltmeter above 200KΩ should be used. Pointer voltmeters with low input impedance cannot be used.
Example: The above figure is an example to illustrate the basic steps of the voltage measurement method to find faults.
⑴Use the voltage block of a multimeter to measure the voltage between points a and b of the MSJ coil. If there is voltage, it means that the fault is on the coil between points a and b. If there is no voltage, the fault is on the interlock switch of the car door in each hall of the hoistway.
⑵ Measure the voltage between a and 11 on the top of the hoistway. If there is voltage, the faulty car door switch (MSJ) between a and 11; if there is no voltage, the fault is on the hall door interlock switch of the lower landing.
⑶Measure the voltage between the two contacts of each hall door switch in turn, until there is voltage between the two contacts, this contact is the fault contact.
(4) When processing and detecting elevator faults in high-rise buildings, in order to find the fault point as soon as possible, the "optimization method" can also be used to find the fault. The method is: measure the voltage between 01 and 7 and 02 and 7 on the top of the car on the middle floor, measure the voltage in sections, and the voltage section is the fault section. Such segmented inspections can save half of the time to check out the fault points.

3. Short circuit method.

This is a method of finding faults by short-circuiting each switch node or circuit in the electrical circuit section by section with short disconnected wires. It is basically the same as the voltage method. Special attention should be paid to avoid short-circuiting the voltage of two different phases (poles).
Example: The above figure is taken as an example to illustrate the basic method of short-circuit method to find faults.
⑴ Use a wire to short-circuit the line between 01 and a. If the coil is closed, it means that the fault is on the hall and car door; if it is not closed, it means that the fault is on the coil.
(2) Short circuit between 01 and 11 to the top of the car. If the coil is closed, it means that the fault is not on the car door but on the hall door; if the coil is not closed, it means that the fault is on the verification switch (MSJ) of the car door.
(3) Short-circuit the line between 01 and 9 with a wire. If the coil is closed, it means that the fault is on the switches below 4TMK; if it is not closed, it means that the fault is 5TMK. Short-circuit the hall door switches in this way, and finally the fault point can be detected.
⑷In order to save time when troubleshooting the door interlocking failures of elevators in high-rise buildings, the "optimization method" can also be used to find fault points in segmented short circuits.
Pay special attention to the following points when using the short circuit method:
①The short-circuit method must be carried out when no one is in the car, the hall and car doors are closed, and when it is not in operation.
②In the process of testing with the short circuit method, measures must be taken to prevent the car door from opening to prevent accidents.
③This method should not be used for the main circuit with large current to prevent large current from being generated during contact and accidents.
④For computer-controlled elevators, this method should not be used to avoid damage to the equipment.

4. Open circuit method.

When the control circuit does not operate the electrical components and the circuit malfunctions, it means that the circuit may have a short circuit. If this type of failure occurs, you must stop using it immediately to prevent the misoperation from causing personal injury. Disconnect the suspected faulty circuit. If the fault disappears, check the suspected circuit, which may be the fault point of the short circuit.

5. Alternative method.

The substitution method is often used when a circuit board or a plug-in fails, and a good electrical device is used to replace the electrical device suspected to be the fault point to determine the location of the fault. When using this method, it should be noted that the peripheral circuit connected to the circuit board or the plug-in unit must be excluded before replacement, or the new circuit board will be damaged. On the contrary, if a circuit board that is suspected to be faulty is used to replace a circuit board in a normal state, attention should be paid to whether the circuit board itself has any components damaged, which will cause damage to the circuit components in the normal state and magnify the fault.

6. The sound method. 7. Light test method. 8. The electroscope method.

9. Procedure inspection method.

Procedure inspection method When debugging, overhauling, transforming and carrying out large-scale system troubleshooting, cut off the power supply of the motor and the brake, according to the requirements of the electrical schematic diagram and operation manual, short-circuit the contacts and contacts that are not enough for operating conditions, artificially The ground creates a working condition for the logic control circuit or the PC ladder diagram to meet the requirements of motor starting, rapid deceleration, braking leveling, parking, opening and closing operations. Then use the short-wire short-circuit method to add position signals, call signals, and command signals to the control frame, and observe whether the wiring of each part and link in the control system is correct, and the sequence of each output signal is in line with the elevator operation sequence.

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