Tech Primer
Water meters are the instruments that can be found in most families now for the measurement of water consumed by residents. Traditional water meters use mechanical structures, measuring water flow by rotation of the wheels installed inside meters. These meters have low precision, require manpower for meter reading, and are vulnerable to water stealing.
With the massive introduction of new technologies such as microprocessors, sensors, smart cards and automatic remote meter reading technology, these water meters became smarter than before. They use flow sensors or hall sensors to detect the water flowing through valves and MCUs to calculate the actual amount of water consumed by users. Apart from measuring water electronically, they integrate many other functions including fee calculation, data storage, records review, and remote automatic meter reading. Comparing with traditional meters, smart water meters provide higher precision and reliability, lower power consumption, longer service life and easier installation and use.
A typical smart water meter is composed of contact/contactless smart card reader, flow sensor, voltage detection IC, instrumentation amplifier, ADC, Tamper detection circuit, MCU, LCD display, WLAN transceiver, buzzer and indication lights, driver circuit, battery and power management circuits. The contact/contactless smart card reader is used to check the identity information stored in a user card and then read the balance (available water amount) by contact/contactless method (RFID technology). The balance information will be passed to MCU, which then calculates and updates the data of available water amount stored in local memory. Meanwhile, MCU sends an instruction to open the water valve. When a user opens a water tap, flow sensor or hall sensor detects the water flow and sends the collected information to MCU. MCU will calculate the water fee and available water amount based on the price per gallon (or m3) and consumed water amount. All these information are stored in local memory, displayed on the LCD when a user presses the button, and sent to a data collection device within WLAN through the WLAN transceiver, accomplishing the function of automatic remote meter reading. The voltage detection IC is responsible for the monitoring of battery power. Tamper detection circuit can prevent water meters from illegal disassembly and data tampering. Buzzer and indication lights will give warning signals when the available water amount is at a low level.
This solution is powered by battery, thus all the devices used in the design need to meet the requirements of wide operation temperature, low power and small size. In addition, adopting measures as many as possible during design to reduce the system power consumption is also important for smart water to work properly over a long battery life.
Since smart water meters and gas meters share the similar hardware architecture and functions, this solution is suited for both of the meter categories.
At present, the well-known semiconductor companies around the world such as ADI, Atmel, Freescale, GEMS sensor, MEMSIC, NXP, TI and ST can provide devices used in smart water/gas meter such as sensors, RFID devices, MCUs and drivers.
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