# Demand Scan in Ignition OPC UA Server?

**URL:** <https://forum.inductiveautomation.com/t/demand-scan-in-ignition-opc-ua-server/5234>\
**Category:** Ignition\
**Created:** [October 3, 2012, 10:20pm UTC](https://forum.inductiveautomation.com/t/demand-scan-in-ignition-opc-ua-server/5234 "2012-10-03T22:20:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![adamaustin](https://avatars.discourse-cdn.com/v4/letter/a/5f8ce5/32.png) [@adamaustin](https://forum.inductiveautomation.com/u/adamaustin)\
**Post date:** [October 3, 2012, 10:20pm UTC](https://forum.inductiveautomation.com/t/demand-scan-in-ignition-opc-ua-server/5234/1 "2012-10-03T22:20:17Z")

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Is there a way to do a Demand Scan on a single device using Ignition’s OPC UA Server? What about a programmatic way to change how often the device is scanned?

We have numerous devices connecting to an Allen Bradley CompactLogix 1769-L35E (which works great, thank you very much), but we only want to poll once every 10 or 15 minutes unless we push a new value to the device. Then we want to scan immediately to get the new value.

Currently using Ignition OPC-UA Server 2.2.0 (b0).

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [October 3, 2012, 10:24pm UTC](https://forum.inductiveautomation.com/t/demand-scan-in-ignition-opc-ua-server/5234/2 "2012-10-03T22:24:39Z")

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You might be able to get something like this happening by putting your tags for this device into their own scan class and using a combination of “Read” mode (versus Subscribed) and “Driven” mode with a slow rate of 10-15 minutes and a fast rate of ~1 second.

When you want to do a “demand scan” you would flip the driving property on for a few seconds and then back off.