A perennial problem with installing control and measurement systems in industrial environments is cabling. Installing and maintaining the reliable operation of cable networks can be very difficult in factories and larger industrial facilities where buildings may be remote. Roads, railways and even rivers may need to be crossed creating their own sets of health and safety hazards. Cable faults can easily be caused by mechanical damage and the environment resulting in costly lost production and safety issues which could result in life hazard, damage to process equipment and unnecessary plant shut-down.
The recent advent of compact, high reliability short range wireless devices has allowed Deeter to develop a wireless sensor system which can transform industrial control and measuring systems. Greatly reducing the cost and time required to install, increasing convenience and reliability and enabling simple relocation of sensors should factory layout change. In addition Deeter probes are battery powered removing the additional layer of installation complexity of providing mains power in remote locations for conventional measuring instruments.
.A Deeter Wireless Sensor System may include a number of Wireless Routers to form a wireless ‘mesh’ network. This allows signals to be automatically re-routed around any broken links in the mesh creating a built-in self-healing capability to further ensure communications reliability.
The Deeter Wireless Sensor System will be welcomed by control engineers in industrial and manufacturing industries such as food and beverages, cooling systems and agriculture.
System Applications and Features
The Deeter Wireless Sensor System was primarily designed for use in liquid level sensing, to complement the very popular existing range of Deeter float-switches and continuous level sensors. Countless other applications for the Deeter Wireless Sensor system are possible, including:
• remote monitoring of switch inputs to drive relay outputs
• converting a potentiometer input to a 4-to-20mA current loop output
• mirroring a 4-to-20mA current loop signal
• switching relays at preset input thresholds
The System has the following advanced features:
• Sophisticated RF Communications and Wireless Network capability
• Fully automatic operation once the system is installed
• Battery powered remote sensors
The system uses very reliable high power RF transceiver modules and rugged external antennae to achieve the best possible wireless communication range. Range can be further extended by adding one or more Deeter Wireless Routers which receive and re-transmit the signal with increased gain. The Base Station acts as the coordinator for the wireless network and operates in the 2.4GHz ISM (Instrumentation Scientific and Medical) frequency band. This allows the system to be used world-wide without requiring a site radio operating licence. Local regulations may restrict the maximum RF transmit power and Deeter provide different variants of the Wireless System devices for the USA, Canadian and European markets to satisfy these constraints. The IEEE 802.15.4 protocol used in the Deeter Wireless Sensor System allows several networks to share the same frequency without interfering with each other. The protocol uses sophisticated techniques to ensure good communications using very low power signalling. This allows the Deeter Wireless Sender or LVCS-RF (RF Liquid Vertical Continuous Sensor) probe to operate using battery power. Once the system is installed it will operate reliably for extended periods without any further intervention. When several Routers are used they form a ‘mesh’ network, and signals can be re-routed around any broken links in the mesh. Thus, the system has a built-in self-healing capability to further ensure communications reliability.
At maximum transmission power (USA version) the distance between sensor node and Base Station may be up to 4km in an ideal, open field installation. For operation in Europe, regulations restrict the maximum transmission power and a range of up to 1000m may be possible. However, in most practical environments the radio signal will be attenuated by obstructions and by multi-path fading caused by reflections. To improve range, a clearer signal path can often be achieved by increasing the height of the antenna and Deeter supply an antenna extension kit for this purpose. A Deeter Wireless Router placed somewhere between the remote sensor and Base Station, or off to one side of the direct line between the two, will greatly extend the wireless range and up to four Routers may be used in a single system.
There are four devices currently in the Deeter Wireless Sensor product range:
• Base Station
• Wireless Sender
• LVCS-RF Liquid Vertical Continuous Sensor probe
• Wireless Router
A basic Wireless Sensor System comprises a Base Station and a single sensor node, either a Sender or LVCS-RF. A Router may be added to the system to improve communications reliability or to extend the wireless range. Up to four Routers may be used in a single system.
The sensor nodes can accept a range of input devices to suit the application:
• Four switch inputs (Sender only)
• An analogue resistive input (Sender and LVCS-RF)
• A 4-to-20mA current-loop sensing input (Sender only)
The Base Station has a range of outputs to drive a wide variety of possible
• Four open-collector transistors for relay operation etc.
• 4-to-20mA current loop driver
• Serial communications output via RS232, RS485 or USB
(At present, serial communications is reserved for diagnostic data. Future
developments are expected to include data-logging features.)