User`s guide

Page 88

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

6. Application Notes

6.1. App Note: Performance Tuning

6.1.1. General Practices to Ensure Better Performance

To ensure optimal performance, the PLC should at least:

1. Ensure quick responses to the 1746-C requests for an M1 transfer.

(

cuts down 1746-C delaying other operations while waiting for the PLC)

2. Ensure table [0] is set correctly and repeated in a timely manner. Allow for frequent table [0]

reads.

3. Only control & monitor discrete outputs (tables [16 & 17]) if and when needed.

(

cuts down on the time to gather data from each actuator)

4. Only read additional registers if and when the application program requires them.

(

cuts down on the time to gather data from each actuator)

5. Restrict the rate of data writes to the actuators … only write as fast as required to adequately

control the valve.

(

cuts down on the interruptions to scanning the network … gathering data)

6. Only write to or read tables if actually in use.

(

ex: do not write to the analog output table if analog outputs are not used)

(

prevents unnecessary delays to gathering the more important data from the network)

6.1.2. Reading Run-Time Information from Table [0]

The PLC should perform a read of table [0] in a timely enough manner so that an operator can “view”

the run-time changes in a manner that makes sense. For example, the operator should be able to

watch the scan counter increment by 1 or 2 … if it appears to “jump” by 15 or so (because the PLC is

not reading table [0] enough) then it is a lot more difficult to use the information.