Using a 4-20 mA CO2 sensor with a Xenta 102-AX in StruxureWare

Issue

Configuring the Xenta 102-AX to accept a 4-20 mA CO2 sensor input on Universal Input 3.  A negative value is required on the CO2 offset value, but it is not possible to edit the scaling of the input in StruxureWare.

Product Line

SmartStruxure Solution

Environment

Xenta 102-AX

4-20 mA output CO2 sensor

SmartStruxure

Cause

The Xenta 102-AX universal inputs are designed to work with a 0-5V input.  The best option is to always buy a CO2 sensor that is compatible.  However, if 4-20 mA CO2 sensors have already been purchased and installed, they can be made to work.

Resolution

In this example, a 4-20 mA CO2 sensor with a 0-2000 ppm range is assumed.

  1. In the Xenta 102-AX Plug-In > Hardware Configuration Tab, set Input 3 Selection to None
  2. Wire the CO2 sensor and a 250Ω resistor across U3 and M.  This converts the 4-20 mA signal to 1-5V.
  3. In SBO WorkStation, create a Function Block program to convert the 0 to 100 % signal to ppm.  (You can import the Function Block program here).
  4. Edit Bindings on the CO2 Curve program and bind the nvoUnvInput3/Value.lev_percent from the UnivIn3Sense folder of the 102-AX to the CO2_RAW of the CO2 Curve program.
  5. Bind the CO2 from the CO2 Curve program to nviCO2/Value.ppm that is in the UnivIn3Sense folder of the 102-AX.

At this point, if you have values entered in for the Airflow Reset or CO2 Low Limit and CO2 High Limit then the Airflow reset will be active and operational.

Also, if you have multiple CO2 sensors on multiple 102-AXs then you don't have to have a CO2 Curve Function Block program for each one.  You can just edit the existing CO2 Curve program and copy/paste the exiting Function Block program multiple times in the same Function Block program.  You would just need to rename each public point with a unique name. 

Note:  An input of 0V (a sensor that has not been wired yet) will result in an nvoCO2sensor value of 65535 (invalid).