Table 10-2: Network topology, bit rate, and cable length
Bit Rate1 (kbps)
Maximum total cable length (ft)
Daisy-chain topology
Star topology
Full termination
Half termination
No termination
250
500
400
400
125
1200
1000
1000
50
2800
2400
2400
1
Default Bit Rate is 250 kbps. Change with
CPISpeed()
instruction.
10.5 Multiple devices
Multiple GRANITE Measurement Modules may be connected to a single data logger using a
daisy-chain or star topology (see
Connecting multiple GRANITE Measurement Modules
(p. 26)).
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 Bus
, which is available at
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
0
= 5 V – 0.3 V – (30 Ω) x I
0
Where V
0
is the drive limit, and I
0
is the current required by the external device.
20) shows the relationship between supply voltage and current load.
VOLT 100 series
37
