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Tips on Optimizing Most Drivers

FIX IO drivers are highly configurable, compared to other systems that perform automatic configuration of Polled data. FIX IO Drivers will always be as fast or faster than an automatic configuration when properly configured.

Please Note that All FIX drivers achieve the Maximum throughput or bandwidth that your IO system allows (The IO is always the bottleneck). The notes below will help you get the most of a limited bandwidth system. SCADA systems generally do not use enormous amounts of IO, the Following is more for extreme cases with either a Slower PLC system OR a narrow band channel, like a radio telemetry system.

The first step to optimizing your system is to measure this maximum IO bandwidth, then make changes bearing in mind what can realistically be achieved.

How Not to setup Your Pollrecords

The worst way to setup the pollrecords is to add a new pollrecord for each Tag in the database, resulting in 50+ pollrecords each attempting to poll at 1.0 Seconds.

How to Measure Driver performance

If you configure more pollrecords , no errors will occur but you are not actually achieving your configuration update time. In this case the driver just processes each pollrecord in turn. This is not a problem most of the time but as you add more pollrecords your system will slow down & If you need faster update on a specific pollrecord, changing its polltime will achieve nothing.

Optimization techniques

To make a limited bandwidth system appear faster, you have to slow down the updating of less time critical data to give more bandwidth to the critical data. (increasing the pollrate of a pollrecord when the system is already at full stretch will have no effect) The basic principle is - poll only the data that the operator needs for a given picture & at the minimum rate he is prepared to accept. It is usually better to set slow polltimes at the start of a project which leaves plenty of room to expand, this sets a lower expectation and if you need more speed later you have spare bandwidth resources.

How to design Your PLC memory map for optimum SCADA driver performance

Optimizations When Writing data down to the PLC for Continuous Control applications

On most systems writing data down to the PLC occurs so rarely that there is no effect on performance. The only setups where writing occurs continuously are where you need to perform continuous control e.g. a PID loop in the SCADA driving an output in the PLC. Another more common requirement may be to write a value coming from another IO driver e.g. from one PLC to another. In all cases AVOID continuously writing the same value, unnecessarily. Only write changes of state. This normally dramatically reduces the writing overhead.

Read performance will inevitably suffer when continuously sending updates to the IO device. All drivers write data only when the operator changes something OR whenever an AO/DO block is scanned. On Most drivers Reading & writing have equal priority, so READ speed will suffer if you have a lot of writes.


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