View source for Annunciator Dual Sensor Differential Inputs

The annunciator has the ability to use two analog inputs to calculate a differential value on a third input. For example, this setup might be used:

* AI-1: Discharge Pre-Filter, 0-100 PSI
* AI-2: Discharge Post-Filter, 0-100 PSI
* AI-3: Discharge filter differential, -100 - 100 PSI

In this scenario, AI-1 and AI-2 would both be connected to the pressure sensors. AI-3 would not be physically connected to anything, but would calculate the differential value for display, alarms, logging, etc.

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=== Setup ===
A differential input is setup through the following steps:

# Set up both "Source" sensors normally.
# Both source sensors must have the same type (4-20mA, 1-5V or 0-5V) and range
# Select a third analog input for the differential calculation. On this input's setup, select 'Diff' as the sensor type.
# The low/high range buttons will change to 'Low Sensor' and 'High Sensor'. The Diff value calculated will be the 'High' sensor - 'Low' sensor. If the 'High' sensor is lower than the 'Low' sensor, the differential will be negative
# Alarms, gauges, etc., can be used normally for either or both source sensor and the differential sensor. Alarms are not required for each.

In the above screenshot, AI-7 and AI-8 are used for the source sensors and AI-9 are used for the differential calculation. The physical input AI-9 will be empty in this case since the internal math is using that input for the differential.