The level in the ground at which the pore pressure is zero (equal to atmospheric) is defined as the water table or phreatic surface.
When there is no flow, the water surface will be at exactly the same level in any stand pipe placed in the ground below the water table. This is called a hydrostatic pressure condition.
A wireless network uses wireless data connections for connecting network nodes which have sensors cable connected to them to a central location where the data can be viewed. It consists of wireless nodes and a gateway and avoids the costly process of installing cables.
The choice of system will depend on the project parameters which will include access, number and type of sensors, line of sight, barriers and there are several different types of network including:
Mesh Network No central node all nodes are able to communicate to each other.
Star Network Central hub/node to which all the other nodes communicate
Point to point This is the most basic network available and involves one node speaking to another with no other network.
N2G Node (node to gateway) – a data logger unit which is connected to a sensor via a cable that stores and then sends via radio data to a central gateway. It can have single or multiple sensors attached.
D2W Node (direct to web node) – a device which is connected to a sensor via a cable that sends the data directly via GPRS to a website where the data can be visualised.
Gateway – a central location to which wireless nodes transceiver their data and from where the data is then available for access. The data can be accessed either directly via Ethernet or Wi-Fi to a webrowser or via GPRS to a website where it can be viewed and/or downloaded.