Technical Support

With the progress of society and industrial development, the global water resources are increasingly tight, and our government has clearly proposed in the "Eleventh Five-Year Plan" outline: "We should put water conservation in a prominent position, establish a reasonable water price formation mechanism, comprehensively implement various water conservation technology measures, develop water-saving enterprises, and establish a water-saving society. society." It is expected that in the near future, the demand for various types of water meters will increase significantly. The intelligent water meter that can meet the step price will become a major tool for building a water-saving society.

I. Application of NEC MR Sensor in electromechanical water meters

1、The working principle of electromechanical water meter

Electromechanical water meter, also called intelligent water meter. It is a water meter that converts the original mechanical water meter reading into an electrical signal by installing a sensor element at a certain position on the reading plate pointer or gear set of the water meter, and then performs data processing through a microcontroller to realize a kind of water meter for flow measurement.

2、Comparison of MR sensor and other sensors

At present, in the electromechanical water meter, the most widely used sensors are: Wegan, reed switch, Hall and MR Sensor, because the electromechanical water meter is generally powered by the battery, there are high requirements for the power consumption of the sensor. The difference in power consumption, lifetime, response frequency and magnetic damping of different sensors will have an impact on the accuracy, precision and lifetime of the water meter.

3、The performance of NEC Yamanashi MR Sensor

NEC Yamanashi MR Sensor is a magnetic switching device that uses the magnetoresistive reaction principle to vaporize a strong magnetic metal alloy film on the IC circuit. Its features are:

High sensitivity, high accuracy - Consistency of sensitivity up to 6 gauss or less.

High reliability - Built-in temperature protection circuitry significantly improves the stability of temperature characteristics.

High response frequency - up to 10KHZ.

Low power consumption - overall power consumption is less than 1uA.

Low cost.

Small package SMT.

Due to the above features of NEC Yamanashi MR magnetic sensors, they are well suited for electromechanical water meter applications. High response frequency, which can reach 10 kHz or more, so that the impeller speed can be measured directly to get the instantaneous flow rate of the water meter, which can monitor the water usage in real time. Using two TMR sensors, the rotational speed and direction of rotation of the impeller can be obtained based on four different state signals. By measuring the rotational speed of the impeller, the NEC Yamanashi MR sensor can achieve:

Instantaneous flow detection.

Leakage and high flow rate alarm.

Backflow detection.

4、Application of NEC MR Sensor in water meter

(1) Horizontal direction detection: Using a long or cylindrical horizontal magnetized magnet, MR Sensor and the magnet are in the same plane, and the magnet rotates with the impeller. The MR Sensor outputs a square wave signal, which can get the rotational speed of the impeller, and then the instantaneous flow rate can be calculated. If 2 magnetoresistive chips are installed, according to the four states, the rotation speed and rotation direction can be obtained, and counterflow detection can be performed.

2) Vertical direction detection:

A long or cylindrical horizontal magnetized magnet is used, and the MR Sensor is installed above the magnet, which rotates with the impeller. The MR Sensor outputs a square wave signal, and the rotational speed of the impeller can be obtained, and the instantaneous flow rate can be calculated. If 2 magnetoresistive chips are installed, the rotation speed and rotation direction can be obtained according to the four states, and counterflow detection can be performed.

Second, ultrasonic measurement in the application of electronic water meters

1, ultrasonic measurement principle

Time difference method of ultrasonic measurement is the use of a pair of ultrasonic transducer phase alternately (or simultaneously) send and receive ultrasonic waves, through the detection of ultrasonic waves in the medium of downstream and countercurrent propagation time difference to indirectly measure the fluid flow rate, and then through the flow rate to calculate the flow of an indirect measurement method.

2, Germany ACAM company for the ultrasonic water meter market launched TDC-GP22

(1) TDC-GP22 technical core

TDC - that is, the time-to-digital converter (Time-to-Digital Converter), which uses the absolute time delay of the signal through the logic gate to accurately quantify the time interval.

TDC time measurement unit

The diagram above shows the main architecture of this absolute time measuring TDC. The smart circuit structure on the chip, the guarantee circuit and the special wiring method allow the chip to precisely note the number of signals passing through the gate circuit. The highest measurement accuracy that can be obtained by the chip is basically determined by the minimum propagation delay time of the signal through the internal gate circuit of the chip.

The measurement unit is triggered by the START signal and stopped when the STOP signal is received. The time interval between the START signal and the STOP signal can be calculated from the position of the ring oscillator and the count value of the coarse value counter for a measurement range of up to 20 bits. The minimum resolution of the GP22 is 22 ps at 3.3 V and 25°C. Temperature and voltage have a significant effect on the propagation delay time of the gate circuit. The errors caused by temperature and voltage variations are usually compensated by calibration.

2) Characteristics of TDC-GP22

100% Function & Pin & Register Compatible with TDC-GP21 (1:1 replacement available).

Time measurement accuracy can be selected up to 22ps.

Temperature measurement accuracy: 2mk rms

Temperature drift of TOF time of flight difference: <0.3ps/k

Static current: <0.1uA@85°C

Sleeping current: 1uA (under 32K continuous operation)

Optional part: provide the complete analog part required for ultrasonic water meters

Internal chopper-stabilized internal low-noise comparator (comparator triggeroffset range ±35 mV) and low-crosstalk analog switch, solving the customer's analog section design problems, improving the system measurement quality.

Internal integrated low crosstalk analog switch

(3) TDC-GP22 in the ultrasonic water meter application advantages

High precision time measurement unit, the resolution of 22ps, for the application of time difference method flowmeter provides the basic measurement guarantee, so as to achieve high precision, large range ratio design.

Intelligent first return detection function, so that the time window setting is no longer affected by the time difference change, so as to achieve accurate pulse interval measurement, and backflow, empty pipe identification and alarm.

The first wave pulse width detection function enables the detection and alarm of bubbles and coverings in the pipe section.

Automatic processing to calculate three pulse results and give the average value, simplifying the algorithm processing and saving the resources of microcontroller.

Applications that can use higher frequency >1MHz transducer (due to the shortening of one cycle time, it will make the time window setting very difficult, while GP22 can perform perfect automatic setting)

3, TDC-GP22 in the ultrasonic water meter application program

TDC-GP22 is specially designed by ACAM for ultrasonic water meters. Its high-precision time measurement function provides the basic measurement guarantee for the application of time difference method flowmeter; and the pulse generator of TDC-GP22 can directly drive the ultrasonic transducer in the flow measurement of small pipe diameter, without the need to add another driver chip; the low-power consumption characteristics of TDC-GP22 measurement makes the overall power consumption of the flowmeter significantly reduced, providing an excellent solution for battery-powered equipment. Overall, high-precision time measurement, simple external circuitry, integrated internal signal processing algorithms, ultra-low overall power consumption makes the TDC-GP22 is the ultrasonic water meter designer's choice!