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Shanghai Electric Utility Uses Machine Vision To Read Meters

By the end of 2002, the city of Shanghai had topped over 13 million permanent citizens. Take a moment to ponder the number of dwellings and businesses where those people live and work, and it's easy to consider the kinds of challenges the Shanghai Power Corporation faces each day. About a year and a half ago, the utility began updating its clients' electricity meters, a process expected to take between five and ten years! That means collecting hundreds of thousands of kilowatt/hour meters from customers' homes and businesses and replacing them with newer, more accurate models. The utility also wants to record and store the final readings from all of those meters, but entering that data proved to be a more daunting task than actually collecting the meters themselves. Shanghai Electric Power Corporation wanted to ensure accurate records for all the meters, a procedure that demands automation, but gets some help from human hands.

In March 2005, Shanghai Power Corporation contacted Microview Science & Technologies Inc., a systems integrator based in Beijing. "One of the essential requirements," recalls Yu Zhao, Applications Engineer at Microview, "was to capture images of the meters and read the data simultaneously - both the bar code and the numeric characters - and store the results in a database."

The process appears simple enough. The meters are collected and placed into a carton according to their size. One carton holds eight 1-phase meters or three 3-phase meters. At the plant, a worker places the cartons on a conveyor belt that brings them to the workstation, where an operator then shunts the camera into position through a 3-axis manipulator. When the camera is in the correct position, the operator manually triggers the camera. Once the picture is taken, image processing algorithms read the meter's barcode and the numeric digits (which determined electricity usage) and is compared with the old data. The image, bar code result and numerical reading are stored in the database, and the camera takes the image of the next meter which is analyzed in the same manner. When the procedure is complete for all the meters in the carton, they travel to the end of the line where they are sorted according to their results. Some are destroyed and others are sent to smaller cities to be re-used. Says Zhao, "Given the scope of this project, industrial automation has greatly improved the efficiency of the production line."

The system

Microview's solution uses an IBM Server X346, 3 Dell 5150n workstation computers, 3 Matrox Imaging Iris P1200 smart cameras fitted with a Pentax CCTV 12mm lens, 3 OEM light sources, 4 Santek MT500/1000 UPS devices, and one TP-Link 100M/16-port device. The image analysis is performed by the Coder Reader and String Reader modules from the Matrox Imaging Library. "The image processing software is extremely important to the application," explains Zhao. "Because the meters display both numerals and a bar code, we needed a solution that could handle the two different input types simultaneously." Zhao says they considered other machine vision vendors, but changed their minds when that meant purchasing two discrete vision systems, one for bar codes and one for character-reading. "With the Matrox Imaging Library we could read strings and the bar codes with a single machine vision system, and that allowed us to keep costs down," he notes.


The user interface.

Challenges in development

Since the image capture process would be manual, Zhao and his team placed a high priority on simplicity and flexibility. The image capture software has two modes, one for the 1-phase meters and one for the 3-phase meters; the operator only has to reset the software type at the workstation to account for the different sizes. The meters themselves presented a more difficult situation. First, the thousands of different model types employ different fonts, which would make defining the font extremely cumbersome, if not impossible. Next, the meter's face features numbers that are not part of the dials (such as a serial number), which could interfere with the character-reading result. The plastic casing on the meter is often dirty, which can also interfere with the character-reading. Finally, the backgrounds of the dials are both black and white, which adds an extra step in specifying the read operation's settings. Finally, the white numeric dials with black numerals lie within a black rectangular frame which has the potential to confuse the read operation. The robust nature of MIL's String Reader module proved invaluable; defining/locating the string and their associated fonts is performed quickly, and the read operations are robust enough to read characters in poor or non-uniform lighting. In some cases, one of the meter's indicators may be between two values and cannot be 'read' by the String Reader; at such times, the operator must manually check the meter and record its value at the workstation.

"We could keep costs down by working with Matrox, " explains Zhao. "By developing with MIL we had all the image processing tools in one package and achieved very accurate results." Integrating the system with the Iris smart camera meant working with a single vendor, which prevented compatibility issues. Zhao's team programmed the application with MIL on the PC for image capture, pre-processing, barcode reading and character reading. Soon the application will be run on the Iris camera itself, since the Windows CE operating system facilitates programming on the camera directly. "We also received excellent technical support, which was very important to us," adds Zhao.


The differences in the meters brought challenges to the project. Note the meter in the center has 5 characters to read, while the others have 6. The center meter's right-side digit is between two values; the operator must manually record this reading.

Now and in the future...

Presently, Microview has deployed a three-workstation system at Shanghai Electric Power Corporation, and there are plans to integrate an additional two workstations. They also hope to sell the system to Shanghai's other power utility. Considering features such as reading different input types simultaneously with a high level of accuracy, and the flexibility to develop the system as the customer's needs change, Microview's shouldn't have to try hard to find customers. But Zhao intends to get the most out of this technology and adapt it for other machine vision applications.

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