Optical Detection of Water Meter Pointer Rotation




Smart meters allow water utilities to streamline meter reading work and to resolve meter reading difficulties, and allow customers to view water consumption amount and allow to receive over-watch services, etc. However, mechanical water meters widely used in households do not have any means to output integrated values externally, and so new smart meters need to be installed. Thus, we are developing technology for externally outputting integrated values, in order to convert mechanical water meters into smart meters.


This technology is to optically detect pointer rotation of a water meter and to calculate integrated values from the rotation number. The device simply consists of a LED and phototransistors. It emits light from the LED onto the dial face and receives the reflected light by the phototransistors. It detects rotation by when  the reflection light becomes weak due to the presence of the pointer at the reflection point. This technology allows to convert from integrated values of mechanical water meters to electric data and allows to add electronic water meter function. Moreover, mechanical water meter without communication function can be changed into a smart meter.



The device emits light from the LED onto the pointer and detects rotation by examining
reflection intensity change by the presence / absence of the pointer.



Correct Detection of Continual Positive/Negative Rotation (Patent pending)

A LED is placed between two phototransistors (PT1 and PT2), so that the pointer is detected simultaneously. This allows detection of rotation even if the pointer stops at any point and changes its rotational direction. For example, if the pointer is detected by PT1 and PT2 simultaneously and then changed to be detected by PT2 only, it means and is found that the pointer has rotated in the normal direction.





Preventing Technology for  Misdetection due to Temperature Change (Patent pending)

Adding a phototransistor for temperature correction (PT3) prevents misdetection of the pointer due to temperature change. The thresholds for the signals of PT1 and PT2 are determined to detect the pointer. Therefore, if the signals change beyond the thresholds due to temperature, the pointer may be misdetected. Thus, PT3 is placed where the pointer is not detected, and thereby the signals only affected by temperature change are identified. It reduces its temperature effect and prevents misdetection of the pointer by acquiring the differences between the PT3 signal and the signals of PT1 and PT2 which are for detection of pointer rotation.





Voice of engineer



Since joining the company in 2014, he has always been trying to have curiosity and to pursue new technologies in a wide range of fields beyond his scope of work.


■What kind of issue did you face and what kind of discovery did you make in the light pickup?

We had an idea to obtain stronger detection signals by lengthening distance at which the pointer is detected. Then we consider to array the three elements on a straight line to shorten distance between the LED and the phototransistors. Although having stronger detection signals, the distanced between two signals is too far and the pointer can not be be detected by the two phototransistors simultaneously. If failing to detect the pointer simultaneously it may result in a misjudgment of the rotational direction. We thus found that when the phototransistors are closer together with the LED placed on the straight line between them, it is possible for them to detect the pointer simultaneously and helps to detect rotation without misjudgment.




■Then, what kind of action or solution did you adopt?

We examine detection signals changes associated with a more suitable positioning between elements, and arrayed elements on an electronic substrate in various arrangements. Even though the elements were arrayed by a mounting machine tool, they were tilted and it affected to detect signals. It results test substrate can not be useful for examining optimal element arrangements. We thus adjusted the solder amount for mounting that the elements not to be tilted. We solved this tilting problem and made a progress of arrangement examination method.




■Talk about further or future improvements.

In some installation environments or during meter reading, the reflection light from the dial face may get into the sensor. It is possible that signals cannot be detected due to the phototransistor saturation. Therefore, we make the sensing area smaller or weaken light strength by keeping proper distance from the entrance position of light. Thus we prevented sunlight from getting into the sensor. In future, we will consider other methods to reduce sunlight effect more by infrared light cut-filter and etc.,.



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