Table 9-4: Network topology, bit rate, and cable length
Bit Rate
1
(kbps)
Maximum total cable length (ft)
Daisy-chain topology
Star topology
Full termination
Half termination
No termination
1000
50
1
not viable
500
200
200
100
250
500
400
400
125
1200
1000
1000
50
2800
2400
2400
1
Default Bit Rate is 250 kbps. Change with
CPISpeed()
instruction.
9.5 Analyzers and channel numbers
Up to fifteen analyzers can be connected to a GRANITE data logger through the CPI network.
NOTE:
Each analyzer requires the same system bandwidth whether or not all channels are active.
The sample rate determines the maximum number of vibrating wire sensors that can be
measured in a VWIRE 305 CPI network. See the seventh and eighth column in
NOTE:
These channel counts do not account for other devices on the CPI bus or other measurement
or computation loads on the data logger.
Use the CPI calculator at
www.campbellsci.com/downloads/cpi-calculator
to estimate the usage
and capacity of a CPI network. To avoid skipped scans and frame errors with a VWIRE 305
network, the CPI bus load should not exceed 75%.
9.6 Data logger program
The data logger controls and collects data from the VWIRE 305, and the CRBasic program
controls the data logger. In most applications that use one analyzer, let DVW Toolbox generate
the program. After setting up the VWIRE 305 and sensors, generate the program by clicking the
CRBasic Code button in the main DVW Toolbox window. Save the program to a file, or copy and
paste the displayed code into the CRBasic Editor.
VWIRE 305
33
