The NETWORK Interface
Up to 32 dataTaker 500/600 series loggers can be connected into a network, where individual loggers are linked together via their NETWORK interfaces.
Note : The dataTaker 50 does not provide networking capability.
The network for dataTaker 500/600 series loggers can be up to 1000 meters (1100 yards) in length. The maximum length of the network cabling is limited only by the attenuation of the communications signals. Therefore data quality cable should be used where long distance networks are to be established, while simple telephone cable is sufficient for short distance networks.
The NETWORK interface of the dataTaker 500/600 series loggers is implemented as a RS485 serial interface, and communicates at a fixed 1200 baud. The interface is not electrically isolated, and is powered from the logger.
There are no master or slave units in a dataTaker network. The host connects to the network via the RS232 COMMS of any dataTaker in the network. All dataTakers in a network have equal status, and each is identified by its unique network address.
A proprietary clash detection and error correcting protocol operates to ensure error free transmission on the network. However this can slow network communications if a number of loggers are trying to communicate simultaneously. The network should be managed such that only one logger is communicating at any one time.
Wiring a dataTaker Network
The NETWORK interface has screw terminals located beside the 9 pin D connector for the RS232 COMMS interface. The screw terminals are labelled NET + and NETñ.
Figure 18 ñ Network Cabling Schematic for dataTaker 500/600 Series Loggers
Figure 19 ñ Network Terminals for dataTaker 500/600 Series Loggers
A dataTaker network is established by connecting the positive terminals of each logger in the network together, and connecting the negative terminals of each logger together.
It is recommended that shielded network cables be used. The shield continuity between successive dataTakers is maintained via the GND terminals of the loggers. The network cable shields should be grounded at one point only, and care should be taken that the shield is not grounded at any other point.
Each dataTaker in a network must have a unique network address. The network address is set via the Network Address switches of the DIP switch. The DIP switch is located behind the memory card connector, under the battery cover.
The Network Address switch settings of the DIP switch for the 32 available addresses are illustrated in Figure 20 below.
The use of the network address when sending commands to a group of dataTakers that are connected in a network is discussed in the Section III ñ dataTaker Networks.
Figure 20 ñ Setting the Network Address of the dataTaker 500/600 Series Loggers
The Network and Modems
The dataTaker network can be extended by modems or radio modems that are able to operate at 1200 baud and can automatically 'turn around' (change direction of data transfer). This is an important issue for radio modems, where changing from transmit mode to receive mode can take as long as 500 mS.
The dataTaker network turn around time is defined by the Parameter7 command in increments of 14 seconds. For example the command
sets the turnaround time to 300 seconds.
The dataTaker does not issue an electrical signal or a message preamble to indicate turn around. The modem must detect when the dataTaker is sending data, and rapidly switch to the transmit mode.
Networking and Low Power Mode
When the dataTaker is asleep, the logger will not wake when network activity begins. To ensure proper operation of loggers in a network, the following should be done
the loggers can be kept awake by setting Parameter15=2
the Wake terminals of all networked loggers can be linked together such that when one logger wakes they all wake
diode couple the negative network wire between loggers to the Wake terminal of each logger. Any activity on the negative network line will then wake all loggers. The diode is necessary to prevent the 10 Hz signal which is output from the Wake terminal while the logger is awake, from entering the network.
dataTaker 50 Address
The dataTaker 50 can be assigned an address, which provides a form of password security to the logger.
Figure 21 ñ Setting the Address of the dataTaker 50
The address can be set in the range of 0 to 15 by the four Address switches of the DIP switch under the top cover of the logger.
The use of the dataTaker 50 address when sending commands is the same as when commanding a network of dataTaker 500/600 series loggers. This is discussed in the Section III ñ dataTaker Networks.