Comparators — Greater Than, Less Than, Equal

School Maths Class — Already Learned This

Teacher asks: "Is 23 greater than 24?" You compare two numbers and give one answer — yes or no. That is a comparator.

Greater Than ( > ) — Pressure Cooker

Safety rule: if pressure exceeds 2 bar → release valve opens.

Pressure 1.8 bar  →  1.8 > 2.0?  →  FALSE  →  Valve stays closed
Pressure 2.3 bar  →  2.3 > 2.0?  →  TRUE   →  Valve opens

BMS example — high temp alarm:

Supply air temp = 19°C, limit = 18°C → 19 > 18 → TRUE → Alarm raised

Less Than ( < ) — Home Water Tank

Low level: if level drops below 20% → pump starts.

Level 45%  →  45 < 20?  →  FALSE  →  Pump stays off
Level 15%  →  15 < 20?  →  TRUE   →  Pump starts

Equal To ( = ) — Lift Door

Lift door opens ONLY when cabin is exactly at floor level. Not above. Not below. Exactly equal.

Cabin at Floor 3 = Floor 3 sensor → Equal → Door opens

BMS example — Modbus register verification during commissioning:

Expected value = 100, read value = 100 → Equal → Communication verified
Expected value = 100, read value = 87 → Not equal → Check wiring

Related Topics

• What is BMS integration? — how a BMS connects with VFDs, energy meters, BACnet/Modbus devices and other building systems
• How to design a BMS system step by step — the complete BMS design methodology covering site survey, IO list, controller selection, sequence of operations
• What is a Building Management System (BMS)? — fundamentals of BMS controls and architecture for HVAC, lighting, energy and access
• What is BMS commissioning? — the disciplined commissioning process that turns a BMS install into a working building brain
• Browse all Control Loops & FBD topics — more from this section of the EnSmart BMS Library