User`s guide

Page 42

Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)

5.3.2. Table [0] Configuration Words … Words [4



17]

The following words in table [0] are a configuration and control parameters set by the PLC for the 1746-

C to run as expected.

Word [4]: Number of Actuators on the network.

This is value indicates of the number of actuators on the network. If this number ever changes,

all tables [1-20 … except for 15] are reset to ensure valid values get filled for each valve on the

network.

The minimum number of actuators is one (1).

The maximum is 60 (which is also the default).

Note to Remember with PLC Interfacing:

The 1746-C only fills in tables with data from the actuators during the “network scan time

slice”.

If the PLC changes the Number of Actuators on the Network

at some point in time

after initial power up, the 1746-C will only be filling in the new data “X” actuators at a

time (where “X” is the number of valves scanned per network scan time slide … see

word [7] for more information on this). This means that it can take several network

scan time slices for the 1746-C to fill in new data for all actuators on the network.

The 1746-C will not attempt to fill in all data before interfacing with the PLC again

because of the time it takes to poll the entire network … this could lead to “starving the

PLC” with a lack of communication.

The PLC RLL needs to be constructed to take this into consideration.

Word [5]: Number of Scans in Scan Period … Scan Period “Size”.

The scan period is the number of network scans before the network is retested for network

failures (before the next diagnostic scan).

The default is 50 scans. If there is a communication error, such as a broken communication

cable, then the system will look for a change (such as a repair to the cable) every 50 scans.

The diagnostic scan resets all communication error indicators so that both ports can be checked

The minimum scan period number is five (5). The maximum number is 200.

Note: If your system requires highest performance and speed, then you may want to raise this

value (200 is max). If the system does not require performance but requires high

reliability and early communication fault detection, you might want to lower this number (5

is minimum).

Note:

For more information on using the scan period value and the diagnostic scan; refer to

the Application Note at the end of this document.