This module is responsible for generating a status value for AHUs that use a single analog input to test for fan status for a fan array. Individual fan status devices are wired in series with a resistor across the contact, and one additional resistor wired in the circuit permanently to prevent short circuiting the input. All resistors must have the same resistance value, and this value is entered in the Resistance per Fan input (default value = 100 ohms). See Figure 1 for a suggested wiring implementation to match this module.
Closing the contact decreases the total resistance a fixed amount per activated device. If the total measured resistance is greater than the minimum number of running devices multiplied by the resistance per device, the unit fan is off. If the measured resistance is less, then the unit fan is considered to be operating properly. The module outputs the number of running devices, the effective fan status, and a Boolean output of the fan status.
