What Is the Difference Between AI, AO, DI & DO Modules?

The Founder's Explanation (Teach Exactly This Way)

"Think of your own body. Eyes and skin — they read, temperature, light — that is input. Hand — it acts, opens a tap slowly or fully — that is output with range. Ear hearing yes or no bell — that is a digital input. Finger pressing a switch on-off — digital output. AI AO DI DO — same four things, that is all."

Teaching the Concept

Your Own Four Senses Your eyes read how bright a room is — a range, not just on or off. Your hand turns a tap a little or a lot — an action with strength. A doorbell tells you yes-someone-is-there or no. A light switch you simply flip on or off. Reading a range, giving a range, reading on/off, giving on/off — four jobs, and every BMS point is one of them. A BMS splits its field points into these exact four channel types. The Four Channels ``` READS (input) ACTS (output) ANALOG AI AO 4-20mA / 0-10V 0-10V temp, %RH, pressure valve, damper DIGITAL DI DO volt-free contact relay / triac status, fault, flow pump, fan, light ``` Why Choosing Wrong Hurts Wire a temperature sensor to a DI that can only see on or off, and it will never read a value. The mistake hides until commissioning, when nothing makes sense. ``` Room Temperature -> AI (0-10V sensor) Chilled Water Valve -> AO (0-10V actuator) Fan Run Status -> DI (contact from starter) Fan Start Command -> DO (relay to contactor) ``` Read the direction and the signal type right, and the module selection falls straight out of the IO list.

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Related Topics

• What are analog and digital signals in BMS? — a range versus an on/off state
• What are 4-20mA and 0-10V signals? — the common analog signal standards
• Browse all IO List & Wiring topics — more from this section of the EnSmart BMS Library