DDC Controller Selection Calculator

Controller I/O count from field device schedule.

Analog inputs (AI)

Analog outputs (AO)

Digital inputs (DI)

Digital outputs (DO)

Spare I/O capacity (%)

Controller Size

Tab to move between fields

Controllers required

Total hardware I/O77

I/O with spares93

Total I/O capacity102

Actual spare (%)24.5

Bottleneck I/O type3

Spare AI points6

Spare AO points9

Spare DI points4

Spare DO points6

Controller cost ($)$5,400.00

Expansion Alternative Cost$4,600.00

How to Use This Calculator

Enter Analog inputs (AI), Analog outputs (AO), and Digital inputs (DI).
Set Digital outputs (DO), Spare I/O capacity (%), and Controller Size.
Adjust Small/Unitary (16 I/O, $800), Medium/Application (34 I/O, $1,800) as needed.
Review the Controllers required result.
Use Total hardware I/O and I/O with spares to inform your decision.

How the result changes with Analog inputs (AI)

Analog inputs (AI): Total analog input points: temperature sensors, pressure transducers, humidity sensors, CO2 sensors.
Analog outputs (AO): Total analog output points: valve/damper actuators (0-10V), VFD speed commands (4-20mA).
Digital inputs (DI): Total digital input points: run status contacts, alarms, flow switches, filter status.
Digital outputs (DO): Total digital output points: start/stop relays, enable signals, 2-position valve commands.
Spare I/O capacity (%): Reserve spare I/O for future expansion. Industry standard: 15-20%.
Controller Size: Select DDC controller size class

Controllers required: Minimum number of DDC controllers needed to serve all I/O with spares.
Total hardware I/O: Sum of all physical I/O points (AI + AO + DI + DO).
I/O with spares: Total I/O count after adding spare capacity percentage.
Total I/O capacity: Actual I/O capacity of the selected controllers.
Actual spare (%): Actual spare I/O percentage achieved with the selected controllers.
Bottleneck I/O type: Which I/O type drove the controller count: 0=AI, 1=AO, 2=DI, 3=DO.
Spare AI points: Unused analog input capacity across all controllers.
Spare AO points: Unused analog output capacity across all controllers.
Spare DI points: Unused digital input capacity across all controllers.
Spare DO points: Unused digital output capacity across all controllers.
Controller cost ($): Estimated hardware cost for controllers only (excludes wiring, programming, commissioning).

Identify Input Parameters
4 parameters
Analog inputs (AI) = 30, Analog outputs (AO) = 15, Digital inputs (DI) = 20, Digital outputs (DO) = 12 = 6 input(s) provided
Calculate Controllers required
Controllers required
3 = 3
Calculate Total hardware I/O
Total hardware I/O
77 = 77
Calculate I/O with spares
I/O with spares
93 = 93