DPS — Differential Pressure Switch
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The Light Switch Analogy
A DPS is the digital version of a DPT. Like a light switch — it has two states only: contact closed or contact open.
When differential pressure exceeds the set threshold — switch contacts close. Digital Input to BMS = 1 (activated).
Below threshold — contacts open. DI = 0 (normal).
DPS Applications:
FAN RUNNING CONFIRMATION:
DPS across supply fan
Fan running → pressure difference across fan → DPS activates → DI = 1
Fan stopped → no pressure difference → DPS open → DI = 0
BMS confirms fan is actually running (not just commanded to run)
FILTER HIGH PRESSURE ALARM:
DPS set at 150 Pa
Clean filter → DP below 150 Pa → DPS open → DI = 0 (normal)
Choked filter → DP above 150 Pa → DPS closes → DI = 1 (alarm)
BMS raises "Filter Choked" alarm
PUMP FLOW CONFIRMATION:
DPS across pump
Pump running with flow → DP present → DPS activates
Pump running but no flow (closed valve) → no DP → DPS stays open
DPS vs DPT:
| Feature | DPS | DPT |
|---|---|---|
| Output | ON/OFF (DI) | Continuous (AI 4–20mA) |
| Information | Crossed threshold or not | Exact pressure value |
| Cost | Lower | Higher |
| Use | Simple alarm or confirmation | Control and trending |
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 Sensors topics — more from this section of the EnSmart BMS Library
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