1. Introduction
With the rapid development of the national economy, high-rise buildings are increasingly common in large and medium-sized cities, leading to a surge in the number of elevators, an essential piece of equipment. Because elevators are directly related to the safety of users, the state mandates annual inspections by specialized quality supervision departments. Traditional inspection methods involve sending personnel to the site to review elevator duty records and manually check various indicators, which is time-consuming, labor-intensive, and fails to objectively reflect the long-term condition and performance of elevators. The remote monitoring system developed by the author installs a data acquisition terminal at the operating site of each elevator, continuously monitoring and recording its operation 24 hours a day. Historical and real-time data from elevators distributed across different locations in the city are remotely retrieved via telephone lines and transmitted to the quality supervision department's upper-level management computer. Dedicated evaluation software then analyzes the elevator's operational status, providing an objective and accurate assessment of its performance.
2. System Composition Structure Diagram
The system architecture is shown in Figure 1. The system consists of a remote upper-level management computer and multiple data acquisition terminals. Each data acquisition terminal is connected to one elevator, collecting various operational statuses of the elevator in real time, analyzing and processing the data, and saving elevator fault information to non-volatile memory. The remote upper-level management computer manages and evaluates elevator performance. When annual inspections are required, it connects to the Public Switched Telephone Network (PSTN) via a modem on the computer to call the on-site data acquisition terminals, inputting the on-site data into the upper-level computer's database for analysis and evaluation. To conserve telephone line resources, a small building complex (e.g., several buildings within 1 kilometer of each other) shares a single telephone line. Only data acquisition terminal 1 is connected to the telephone network. The remaining data acquisition terminals in the complex are connected to the RS485 bus along with terminal 1, using a software protocol to identify terminal numbers and communicate with the upper-level computer.
Figure 1 System Composition Structure Diagram
3. Hardware design of the data acquisition terminal
Elevator systems require monitoring of various information, such as leveling signals, car door locking, hall door locking, upper and lower limits, as well as running acceleration, temperature, and humidity signals. These signals are processed or transformed by sensor circuits, ultimately providing the data acquisition terminal with standard digital or analog signals. Considering practicalities and cost, an 8-bit MCU (microcontroller) with 16 digital inputs and 8 analog inputs can be used. Key technical data to consider for the data acquisition terminal include: acquisition cycle, communication protocol, communication rate, digital signal acquisition, analog signal acquisition, and data storage capacity. The hardware block diagram of the data acquisition terminal is shown in Figure 2. In Figure 2, a modem module is used to communicate with the remote host computer's MODEM via a telephone network. Its output is converted to standard RS485 level by a level conversion chip and then forms an RS485 network with other data acquisition terminals installed on nearby elevators. The latch is used to latch and acquire the input switch quantity. The A/D converter completes the acquisition of analog quantity. The clock chip provides a precise time reference for the entire system. It can generate real-time data such as year, month, day, hour, minute, second, and day of the week. It also has a built-in lithium battery and clock circuit, and can operate independently without external power supply. The MCU expansion module is used to supplement the functions of the MCU. It can add functions such as power-off protection and can also be used to expand the storage space so that a certain elevator can store up to 1 year of historical fault data.
Figure 2 Hardware block diagram of the data acquisition terminal
4. Software Design
4.1 Data Acquisition Software Design for the Acquisition Terminal
The software for the data acquisition terminal is written in Visual Basic. The data acquisition section includes querying digital and analog signals, diagnosing faults, and storing faults in a specific format. This part of the software operates on a timed query basis, with a time interval of 1 second, meaning it queries 16 digital and 8 analog signals every second. If a fault is found in a signal and meets the storage criteria, the fault number and timestamp are stored in the E2PROM. The software flowchart for the data acquisition section is shown in Figure 3.
Figure 3 Flowchart of data acquisition software
4.2 Communication Software Design of the Data Acquisition Terminal
The modem module of the data acquisition terminal operates in called mode. When a call comes in, the software first identifies the caller ID. If it matches the pre-set remote management department's phone number, it sends an AT command to the host computer's modem to respond. At this point, the communication link between the two parties is successfully established. Data transmission can be simply viewed as communication between the MCU's serial port and the remote PC's serial port, with a baud rate of 2400 b/s, no parity, 8 data bits, and 1 stop bit. Data transmission between the data acquisition terminal and the remote host computer uses a command-response method; that is, after the host computer sends a specific command, the data acquisition terminal sends back the corresponding information.
4.3 Design of Remote Host Management Computer Communication Software
The remote host computer is equipped with an external modem. When it needs to communicate with the lower-level acquisition terminal, it first sends a standard AT dialing command to the MO2DEM via the serial port. Once the other party's modem picks up and responds, the communication between the two parties becomes standard serial communication. The remote host computer software runs on the Microsoft Windows XP operating system, and the communication program is written in Microsoft VB6.0, using the MSComm communication control.
4.4 Design of Host Computer Evaluation and Management Software
The host computer-based evaluation and management software is written in VB and mainly includes functional modules such as administrator identification, parameter setting for data acquisition terminals, fault data entry, data analysis and evaluation, and report generation. SQL Server is used as the database management system to store and manage data, forming the backend database engine of the entire application system. VC++ uses ADO (ActiveX Data Object) to connect to the SQL Server database. The advantage of this approach is that VB can easily develop the front-end software, while SQL Server provides efficient database management. In the evaluation software, the annual fault records of a specific elevator entered into the database are first classified according to severity. Severe faults (such as the car door suddenly opening during operation) are classified as Class A, followed by Class B, Class C, etc. Then, the number of faults in each class is statistically analyzed, resulting in a pie chart of each type of fault. If there are too many faults in Class B or above, the conclusion that the elevator is unqualified is printed directly, along with the reasons; if the number of faults is within the acceptable range, the conclusion that the elevator is qualified is printed.
5. Conclusion
During elevator operation, the frequent starting and stopping of the drive motor and the switching on and off of various relays create a highly complex electromagnetic environment. Therefore, interference suppression is particularly important, especially since electromagnetic interference has a strong impact on analog signals, causing significant signal fluctuations. Thus, various anti-interference measures should be implemented for the analog signal acquisition section, such as adding filtering circuits, shielding sleeves, and single-point grounding. The implementation of a remote elevator monitoring system greatly saves manpower and material resources and has high potential for widespread application.
References
[1] Shen Yicheng. Modem User Guide [J]. Shaanxi Electronics Magazine, 2004, (17)
[2] Ren Xia. Remote communication program based on VB [J]. Computer Applications, 2005, (5)
[3] Wang Shichang. Computer System and Network Technology Development and Application Examples [M]. Beijing: Machinery Industry Press, 2003.
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