> For the complete documentation index, see [llms.txt](https://help.boomerang3.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.boomerang3.com/s2gw-installation-manual/s2gw-operation/sensors-initialisation.md).

# Sensors initialisation

After receiving the configuration:

1. If it is the same as the current configuration, S2GW does not perform the sensor initialisation and continues to operate.
2. If it is different from the current configuration, S2GW performs the initialisation for the sensors for which the configuration did change.

In case any sensor fails initialisation, S2GW sends information about fail immediately after the check using [S2GW No answer from a node](/s2gw-installation-manual/troubleshooting/xml_examples/s2gw-no-answer-from-a-node.md) or [S2GW No sensor detected](/s2gw-installation-manual/troubleshooting/xml_examples/s2gw-no-sensor-detected.md)messages.

It presents the reason of failure which can be node not answering on radio ("No communication with node") or node answering but having no sensor with a given index ("No sensor detected (node sends 0xAA)").

If the node/sensor will come online, then it will be discovered by the S2GW after next configuration update. This will happen no more than 15 minutes later assuming default Refresh Config period of 15 minutes, is set in the GW config file.

The initialisation of a single sensor is shown in the flowchart below.

<figure><img src="/files/GuLQx2W4eBs0g2hpChni" alt=""><figcaption></figcaption></figure>

It can be found in S2GW log


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