How to Activate the Discrete Inputs on a Honeywell UDC 3500 Controller

What is needed to activate the discrete inputs on a Honeywell UDC 3500 controller?

A. Analog signal

B. Digital signal

C. Dry contact closure

D. Voltage input

Answer:

The discrete inputs on a Honeywell UDC 3500 controller need a dry contact closure.

The discrete inputs on a Honeywell UDC 3500 controller require a dry contact closure. This type of closure does not have a voltage applied to it by the controller's input circuit; instead, it is a signal sent by either opening or closing a set of contacts, similar to flipping a switch. The controller receives this signal and uses it to make decisions regarding its output controls.

For example, suppose we have a pressure switch that closes its contacts when the pressure in a vessel exceeds a certain value. If we wire this switch into the Honeywell UDC 3500 controller's discrete inputs, then when the pressure gets too high, the switch will close, and the UDC 3500 controller will know it needs to take action, such as opening a valve to decrease the pressure.