Product overview


The product has two main purposes:

  • Measure outdoor temperature at high precision via wireless M-Bus

  • Measure outdoor humidity at high precision via wireless M-Bus

Application description

The CMa20w is a wireless M-Bus communicating temperature and humidity sensor for outdoor use

CMa20w is the ideal product for temperature and humidity report of outdoor climate. The high accuracy sensor and user friendly handling makes the CMa20w the perfect choice for outdoor climate logging.

The CMa20w should be used in the following scenarios:

  • Outdoor measuring of temperature and/or humidity

  • Attic monitoring of temperature and/or humidity

  • Cellar monitoring of temperature and/or humidity

  • Other harsh environment conditions


If measurement of temperature and humidity is needed for indoor use, see Elvaco AB product CMa10w Indoor M-Bus temperature and humidity sensor.

Parts overview

  1. Service connector

  2. LED

  3. Push button

  4. Sensor pipe

  5. Wall mounting

LED indications

When the CMa20w is activated (normal mode) and you push the switch, the LED indicates what mode it is in.

Table 150. LED


Product state

Flashes for three seconds

The product is in unencrypted mode

Permanently on for three seconds

The product is in encrypted mode

Factory default settings

Table 151. Factory defaults





(At delivery, the CMa20w is in sleep mode, where it does not consume any power, and does not transmit any data. It needs to be activated by pressing the button. After that it cannot go back to sleep mode again.)

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