Analog Output Interface

Analog Output

The FAC-2100 has two analog outputs capable of providing 0 to 20mA, 4 to 20mA, 0 to 5V, or 0 to 10V (all modes are software configured). When outputting current each channel also has the option to be wired in source or sink mode.

Two common questions arise when using the analog outputs. First, what is the difference between wiring the output as a current source versus a current sink? The difference between the two is the position of the load relative to the A_OUT+ and A_OUT- pins. In a current sink scheme, the load is attached to the A_OUT+ pin. In a current source scheme, the load is attached to the A_OUT- pin. See the Current Output Mode (Sink and Source) examples. More importantly, as shown the Current Sink Mode and Current Source Mode examples, the position of the grounding point is different. Notice that if a current source is used, the load is attached directly to the circuit ground. This is important if you wish to transmit an analog signal, for example, from a sending controller to multiple receiving controllers. By attaching the load (in this case the load is the analog inputs of the receiving controllers) to ground, the entire circuit can have a common ground reference point. This common ground can become important if a single source is providing power to all the controllers, sensors, and actuators in the system.

The second common question is when should the circuit be wired as a current source rather than a current sink? In general, wire the circuit using the current sink configuration. If you need to transmit an analog signal between controllers, use the current source configuration. The main reason for this preference is that the analog output circuitry in the controller will sink current over a wider range of load conditions in comparison to a current source configuration.

Note that a voltage source from 4 to 32 V DC is required for the analog outputs to work correctly (see the Installation section of this bulletin for additional information). Care must be taken when selecting the source to ensure that grounding loops or unwanted grounding shorts do not occur. Also, the voltage for this analog output source cannot exceed the auxiliary output source. In general, it is recommended that the FAC-2100's internal auxiliary output source be used to power the analog outputs.

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