Sigma - Using an Analogue Input Card to Display Digital Inputs.

[Product_Support]

Issue

In scenarios where no Digital Input (DI) channels are available, users may need to simulate digital input functionality using Analogue Input (AI) cards.

Product Line

Satchwell BAS & Sigma

Environment

Sigma Analogue Input cards.

Cause

Sigma Analogue Input cards are not designed to function as Digital Input cards. However, a workaround can be implemented to simulate digital input behavior using available analogue channels.

Resolution

To configure an Analogue Input to behave like a Digital Input:

1. Create an Analogue Input Object

   • In Sigma System Manager, define an Analogue Input object using a free point number.

2. Configure a Lookup Table

   • Create a lookup table to translate analogue values into digital states:

     Input   Output
     0       1
     15      0
     20      0
     

   • Assign this lookup table to the Analogue Input object.

3. Add Short Text for Display

   • Create a Short Text (e.g., On/Off = %2.f) to represent the digital state.
   • Link this Short Text to the Analogue Input object.

4. Hardware Setup

   • Fit a 1000-ohm resistor across the Analogue Input channel.
   • This resistor acts in parallel with the digital input wiring.

5. Result

   • When the connected digital input changes state, Sigma will interpret and display the result as either 1 (On) or 0 (Off), effectively simulating a digital input.

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Notes

• This method is a workaround and should be used only when DI channels are unavailable.
• Ensure proper calibration and testing to avoid misinterpretation of analogue signals.