# Ignition & Logix Best Practice Tips for better communications

**URL:** <https://forum.inductiveautomation.com/t/ignition-logix-best-practice-tips-for-better-communications/60386>\
**Category:** Ignition\
**Tags:** rockwell\
**Created:** [June 5, 2022, 11:46pm UTC](https://forum.inductiveautomation.com/t/ignition-logix-best-practice-tips-for-better-communications/60386 "2022-06-05T23:46:38Z")\
**Posts on this page:** 1\
**Showing post:** 42

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**Author:** ![nminchin](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/nminchin/32/6911_2.png) [@nminchin](https://forum.inductiveautomation.com/u/nminchin)\
**Post date:** [April 25, 2025, 12:34am UTC](https://forum.inductiveautomation.com/t/ignition-logix-best-practice-tips-for-better-communications/60386/42 "2025-04-25T00:34:13Z")

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I recently decided it was time to actually test the theories with scan rates for different structures in the PLC, and found the results below.

What I found (obviously) backed Phil's recommendations to only read UDT tags and to _ensure_ that _all members_ of them are set to at least read access. However what I found was negligible difference in response rate at 100ms when reading the UDT tags from within different structures (e.g. individual UDT instances at the root/controller level, addressing UDTs within an array, or addressing aliases to UDTs within an array)

Ignition request scan rate for all tests (except one): **100ms**  
Number of instances read: 250 (+800ish UDT tags outside of the test, however all are set to ext access = read/write)  
Driver used: IA's Logix driver  
PLC: L82

| **Test** | **Tag Count** | **Actual PLC Response Rate** | **Request Count** |
| --- | --- | --- | --- |
| Individual UDT instances | 7845 | 100.39ms | 20 |
| **Individual UDT instances, Scan rate set to 1ms, CIP Connection Size = 4000** | 6787 | 1.05ms | 2 |
| Array of UDT instances | 7845 | 101.19ms | 21 |
| Aliases to each item in an Array of UDT instances | 7872 | 100.69ms | 21 |
| **AOIs** with same tags as in UDTs | 7899 | **978.20ms** | 303 |
| Individual UDT instances _with a single member set to External Access = None (Note: SCADA didn't actually read this tag)_ | 7845 | **714ms** | 20 |

(all members set to read/write ext. access)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/9/d97f381701b271d19503c72709481cb28f88c754.jpeg)

(all members set to read/write ext. access, CIP Connection Size = 4000)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/8/6/866d043550f64e135e2399f707b27f9a36e63e87.png)

(all members set to read/write ext. access)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/a/dadf4d56fd4e5991475bc688b8407fc95fd26c58.png)

(all members set to read/write ext. access)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/b/3/b395dc59cf6076b38812b63f2e7f60197a28536a.png)

(all members set to read/write ext. access)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/e/9e8a8e058c1aa5db7242ca0f2bb8e316e1932ac2.png)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/6/e680e87150155fcca2c5e9d3d149e720c5485e52.png)

_Note: I think the slight difference in tag counts is a result of reading 1 or 2 fewer udt/aoi instances, but it shouldn't make much of a difference_

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