Design and Application of Pressure Monitoring Equipment for Split Pipe Network

I. Introduction
The pressure of the pipe network is an important data for the water company to ensure water supply and prevent pipe burst accidents. The respective water companies have fully realized the importance of pipe network pressure monitoring, and have adopted various information methods to achieve it. At present, water companies generally use GPRS wireless equipment to remotely monitor pressure data. The installation methods of monitoring equipment are usually the following two:

[Method 1] Install a pressure transmitter in the monitoring well, and install GPRS equipment, solar energy or mains power supply device on the pole near the monitoring well. The signal line of the pressure transmitter is led to the GPRS equipment on the ground to realize remote data transmission. The working power of the equipment is provided by solar energy or city power supply.

This method can realize real-time monitoring of pipe network pressure data, but it requires breaking roads, digging trenches, and laying cables, which makes construction difficult and costly. Especially when the monitoring well is on the road, this method is difficult to realize.

[Method 2] Install GPRS equipment, pressure transmitter and storage battery in the monitoring well. The GPRS equipment collects the output signal of the pressure transmitter and transmits it to the monitoring center directly. The working power supply of the equipment is provided by the storage battery.

In order to extend the battery replacement cycle, this method can only adopt the working mode of regular collection and regular reporting, and cannot realize real-time monitoring. The monitoring method has the following problems:

1. In some monitoring wells, the GPRS signal is weak or no signal, and the pressure data cannot be reported on time or cannot be reported at all.

2. The battery needs to be charged frequently, which is costly and time-consuming to maintain.

3. The environment in the monitoring well is humid and easy to be flooded, which affects the stability of the equipment.

Based on the above problems, we combined low power consumption technology, 433MHz and GPRS wireless communication technology to design a split water supply network monitoring equipment. The device consists of two parts: a wireless pressure transmitter and a 433M/GPRS dual-mode wireless gateway.

Design and Application of Pressure Monitoring Equipment for Split Pipe Network

2. Product design
1. Working method

A wireless pressure transmitter (composed of a low-power pressure transmitter and a 433M data acquisition communication terminal) is installed in the monitoring well, and a 433M/GPRS dual-mode wireless gateway is installed on the roof, street light pole or special installation pole near the monitoring well And solar power supply equipment, the water supply pipe network monitoring center installs servers and pipe network pressure real-time monitoring system software, as shown in the figure below.

Design and Application of Pressure Monitoring Equipment for Split Pipe Network

The wireless pressure transmitter collects the pressure data of the water supply pipe network and sends it to the outside of the surface well through 433MHz. The 433M/GPRS dual-mode wireless gateway outside the surface well receives the pressure data and then transfers it to the monitoring center through the GPRS network. The effective communication distance of the equipment inside and outside the well penetrating the metal manhole cover can reach 150 meters, making the installation position of the 433M/GPRS dual-mode wireless gateway very flexible and greatly reducing the difficulty of construction.

2. Key technology

2.1, 433MHz and GPRS relay transmission, solve the signal problem.

433MHz communication technology uses the 433MHz frequency band, no application or payment is required. Its significant advantage is the strong penetration and diffraction ability of wireless signals, especially in underground monitoring wells, the advantages are more obvious. However, because 433MHz belongs to ultra-short wave, its transmission distance is limited, and the monitoring points of the water company’s pipeline network are distributed within a range of tens or even hundreds of kilometers. Therefore, the use of 433MHz and GPRS relay transmission methods not only solves the problem of weak GPRS signals in surface wells. The problem has met the needs of remote monitoring.

2.2. Battery-powered low-power design to solve the problem of power supply in the well.

In view of the power supply problem of the equipment in the well, the 433M data acquisition communication terminal in the wireless pressure transmitter specially selects a low-power power supply, CPU and communication chip to reduce the working power consumption and is equipped with a 20AH high-energy lithium battery pack. . The 433M data acquisition communication terminal not only powers itself, but also provides working power for low-power pressure transmitters.

The low-power pressure transmitter has a working power supply of DC 5V, a signal output of DC 0.25~2.25V, and a working current of only microamperes, which truly realizes low-power operation.

In order to further reduce power consumption, the 433M data acquisition communication terminal provides power to the low-power pressure transmitter instantaneously when collecting pressure data. After the data collection is completed, the power supply will be stopped until the next meter reading cycle (the meter reading cycle can be set arbitrarily). Calculated according to the 3-minute meter reading cycle, the battery life of the 433M data acquisition communication terminal can reach 2.5 years.

Communication timing and power consumption diagram:

Design and Application of Pressure Monitoring Equipment for Split Pipe Network

The battery life of the 433M data acquisition communication terminal is easy to calculate.

First, calculate the average current, the formula is as follows:

Iaverage=[It*Tt+Ir*Tr+Is*(T-Tt-Tr)]/T (Formula 1)

Among them, Iaverage: average current;

It: emission current; Tt: emission time;

Ir: receiving current; Tr: receiving time;

Is: sleep current; T: meter reading cycle.

As shown in the figure above:

It = 75mA; Tt = 2s;

Ir = 10mA; Tr =1s;

Is = 0.004mA; T = 180s.

Bring into formula 1 to calculate:

Iaverage = (150+10+0.708)/180 = 0.893mA

Secondly, calculate the battery life, the formula is as follows:

Tlife=C/Iaverage (Formula 2)

Among them, Tlife: battery life;

C: battery capacity; Iaverage: average current.

If C=20Ah, then it is calculated by formula 2:

Tlife = 20000/0.893 = 22396 (h) ≈ 2.5 (years)

2.3. Fully waterproof design is adopted to solve the problem of dampness and easy flooding in the well.

The shell of the 433M data acquisition communication terminal is made of high-quality transparent engineering plastics, which has excellent heat resistance, cold resistance and corrosion resistance; it has good structural stability and electrical insulation, as well as light weight, high strength, compression resistance, and wear resistance. .

433M data acquisition communication terminal adopts all-round waterproof design:

◆ The end caps on both sides of the shell adopt thread compression method, which is easy to install.

◆ In order to prevent the gasket from being squeezed and deformed during installation, the inner gland is directly pressed for sealing.

◆ There are 4 fixed buckles built into the shell, which can prevent the inner gland from rotating when the end cover rotates.

◆ The gasket is made of high-quality silicone material, and the surface is designed with a double-curved shape, which can form two vacuum chambers, an upper and a lower vacuum chamber, to form a vacuum isolation.

◆ The inner gland has a 16mm diameter cable hole (used to connect the signal line of the 433M waterproof antenna and low-power pressure transmitter) and is equipped with imported waterproof connectors to ensure that moisture and water cannot enter.

◆ The waterproof pressure test of the product reached 0.8MPa, and the product did not leak or deform after 72 hours of pressure; after a long-term installation and inspection in the meter well, it perfectly met the design expectations.

Design and Application of Pressure Monitoring Equipment for Split Pipe Network

The low-power pressure transmitter also adopts an absolute pressure design, without an external air duct, which fundamentally eliminates the possibility of moisture and water entering the equipment.

The wireless pressure transmitter composed of the above two parts has an overall waterproof rating of IP68, which is fully adapted to the downhole installation environment.

3. Conclusion
The split-type pipe network monitoring equipment overcomes many problems such as difficult construction, poor signal, high power consumption, and unsatisfactory waterproof effect that are common in current pipe network pressure monitoring equipment. It has been repeatedly tested and on-site in Hebei, Shandong, Jilin and other places. Good results have been achieved in the application. This product provides a reliable, stable and energy-saving product solution for the pressure monitoring of the water supply pipe network of the water company.