FIGURE 9-2. Five-wire sensor connection schematic
9.4.2 CPI network bit rate
A CPI network is capable of operating at 1000, 500, 250, 125, or 50 kbps, depending on your
network configuration (see
Connecting multiple GRANITE Measurement Modules
(p. 15)). This is
the rate that data are transferred from the GRANITE Measurement Module to the data logger.
When multiple GRANITE Measurement Modules are making measurements faster than 1 Hz, it is
important to ensure that the CPI network bit rate is higher than the rate that data is generated by
the GRANITE Measurement Modules within the network.
To calculate how many kilobits per second (kbps) will be generated, use the following equation
for each GRANITE Measurement Module in your network:
Kilobits per second = (number of measurements) × (measurement frequency) × (0.064 kilobits
per measurement)
The network topology and cable length affect the maximum allowable CPI network bit rate. Refer
to
(p. 33) for the maximum cable length allowed for the topology and bit rate your
network requires. The bit rate of the network defaults to 250 kbps and can be changed by using
the
CPISpeed()
instruction in the data logger program.
VWIRE 305
32
