TWO WIRE SYSTEM

Sigra has a two wire data acquisition system which is designed with intrinsic safety requirements specifically in mind. This system was originally designed to monitor flowmeters on gas drainage systems in an underground coal mine. The system uses ultra low power and can monitor 255 nodes over 2 km of a cable pair. Each node may have up to four bridge or potentiometer inputs and may also have two temperature inputs. This configuration may be varied to suit specific client needs.

The system operates by a transceiver receiving a request for information via an RS232 connection from a PC, modem or PLC. This request will refer to a particular node. The wire pair will then be energised and all nodes will wake. They will listen for their address. The node that receives this address will remain awake and all others will return to a sleep state. The energised node will draw power from the wire pair to power and gain information from the connected sensors. It will transmit this information to the transceiver which will then power down the wire pair. The transceiver will then store the information until it is gathered via the RS232 link by the host computer.

The system has uses in areas where intrinsic safety and low power consumption is important. Such uses include the petrochemical industry and coal mines. It is also useful for monitoring geotechical information along underground roadways where radio wave attenuation reduces the use of the radios in the field data logger. Another use for the tool is in gathering information from various levels in a borehole. For example a multi-level borehole packer and pressure transducer system may be monitored by a two wire system alone. The Australian Coal Association Research Program report C8021 Data Handling for Gas Drainage Flowmeters describes the origin and operation of the system.