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Out of Range value displayed on Sigma AI point

Issue

Sigma and BAS - Out of Range value displayed on an AI point when configured as a 0-10V input.

Product Line

Other, Satchwell Sigma

Environment

  • Sigma
  • BAS

Cause

If a 0-10V analogue input rises to above 10Vdc then the point default value is displayed.

Resolution

There are several ways to prevent this happening as follows:

  1. Follow the example in SHD100 / SHD101 - Humidity Sensors can give a DC voltage signal of greater than 10 Volts using a resistor and lookup table.
  2. Or use a Zener diode fitted as per the diagram. Note the maximum input will be the rating of the Zener diode e.g if the Zener diode rating is 9.1V then any voltage from the device higher 9.1V will be pulled back down to 9.1V.

    Zener diodes are available with fixed voltages, the nearest to 10V is 9.1V.

    The Zener diode can be fitted at the sensor end (normally slightly easier) or at the controller. The upper limit of the normal operating range of the sensor needs to be below 9.1V.

    Note: normally a resistor is fitted when using a Zener diode, but because the impedance of the sensor is high, the current will be small, hence the resistor is not used. 
  3. Or use a diode, this will work to where the maximum input rises to 10.6V. The diode needs to be fitted in series with the device BMS signal. A diode will drop 0.6V across it, therefore in this case a revised lookup table needs to be created. e.g 10V in will be 9.4V out and so forth.
  4. Or in the case of feedback from an actuator, the output to the actuator can be restricted to a value e.g 9.5V, this will then restrict the feedback signal. Care must be taken with this method if the actuator is connected to a valve then the performance of the valve and the system it is connected to will be slightly reduced.
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