SLPSTX2 Room Humidity Sensor Inaccuracy

[williamcitrayas]

I have installed SLPSTX2 Room Humidity sensor. the controller read the room humidity sensor using Modbus RTU protocol.

The Room Humidity value of SLPSTX2 is inaccurate, the error value from real measurement is about 10%.

I try to offset room humidity value using modbus RTU on address 54 & 55 holding register as shown picture below. but modscan return "invalid repond from modbus query" message.

how to offset the room humidity value of SLPSTX2?

[David_Purser · Accepted solution]

Using ModScan, it has to be configured for 32-bit float and not using default settings.

• Device ID: Enter the Modbus slave address of the SLPSTX2.
• Function Code: Use 03 for Read Holding Registers.
• Starting Address: Enter 54.
• Length: Set to 2 (since 32-bit float spans two 16-bit registers).
• Display Format:
  • Go to Display → Floating Point.
  • Choose MSRF (Most Significant Register First) or LSRF (Least Significant Register First) depending on the device’s word order.
    • Most devices use MSRF, but if the value looks wrong (e.g., extremely small or large), try LSRF.

Can you reply and correct these instructions, especially the MSRF or LSRF setting you found to work?

[williamcitrayas · Accepted solution]

Thank you for the respond.

I recently contacted the schneider technical support, Turn out that the SLPSTX2 that we used is the old version (Production 2022).

And the version that capable to offset the temperature and the RH is production of 2024 above.

And now the sensor still inaccurate and I can't offset the RH value.

is there any way to improve the accuracy of the RH value of the sensor?

[SantiagoFraile · Accepted solution]

Hi William, How are you? If your intention is to apply an offset directly on the sensor screen, you’ll need to order a new SLPSTX2, as this feature was introduced at the firmware level (on production plant) in June 2024. Currently, there’s no way to field-upgrade existing SLP units. The only option available on-site today is to apply the EBO offset, as David described.

That said, I think the real question is: why are you seeing a 10% RH deviation? Is this sensor installed in an office environment or a different type of application? Remember that Living Space sensors were designed to be used in applications such as: offices, hotels, school, etc. places where environmental airflow is steady. If this is the case, please open a ticket with the support team so they can investigate the sensor’s performance. Rgds.