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Table 10-2: Network topology, bit rate, and cable length
Bit Rate1 (kbps)
250
125
50
1
Default Bit Rate is 250 kbps. Change with
10.5 Multiple devices
Multiple GRANITE Measurement Modules may be connected to a single data logger using a
daisy-chain or star topology (see
In both network configurations, as total cable length increases, the maximum possible bit rate
decreases. Limitations on cable length and baud rate are examined in the document
Physical Network Layouts for the CPI
When including two or more VOLT 100 series devices in the program, the processing mode of the
data logger affects the measurement timing of each VOLT 100 series. In sequential mode, the
VOLT 100 series devices make measurements one after the other, following the order of their
instructions within the program. Conversely, in pipeline mode, the devices start their
measurements simultaneously. Pipeline mode is recommended.
NOTE:
In either mode, measurements that require excitation MUST be made on the same VOLT 100
series that provides the excitation voltage or current.
10.6 Switched voltage output
An SW5V terminal is normally used to operate an external relay-driver circuit because the port
itself has limited drive capacity. Drive capacity is determined by the 5 VDC supply, a Schottky
diode, and a 30 Ω output resistance. It is expressed as:
V
= 5 V – 0.3 V – (30 Ω) x I
0
Where V
is the drive limit, and I
0
20) shows the relationship between supply voltage and current load.
Maximum total cable length (ft)
Daisy-chain topology
Full termination
500
1200
2800
CPISpeed()
Connecting multiple GRANITE Measurement Modules
Bus, which is available at www.campbellsci.com/app-notes.
0
is the current required by the external device.
0
Half termination
400
1000
2400
instruction.
Star topology
No termination
400
1000
2400
(p. 26)).
Designing
FIGURE 8-1
(p.
VOLT 100 series
37
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