Level Sensor (Continuous) and Level Switch
The Water Tank at Home
Every Indian home with an overhead tank knows this experience. Parents ask — "How much water is left in the tank?" Someone has to knock on the tank side and listen to the sound. Or climb up and look in. Time-consuming, inconvenient, sometimes dangerous.
A level sensor eliminates this — the tank level is visible on the BMS dashboard at all times, from anywhere.
Level Sensor (Continuous) — Analog:
Measures level as a percentage from 0 to 100% continuously.
Output: 4–20mA
4mA = tank empty (0%)
20mA = tank completely full (100%)
Any value between = proportional level
BMS reads level every few seconds:
Below 20%: command fill pump to start
Above 80%: command fill pump to stop
Above 95%: high level alarm (overflow risk)
Below 10%: low level alarm (supply disrupted)
Technologies used:
Ultrasonic: sound pulse sent down, echo measured — no contact with water
Pressure-based: hydrostatic pressure at bottom = level (as explained above)
Capacitance: probe inserted, water level changes capacitanceLevel Switch — Digital:
Two states only. Above set level — contact closed. Below — contact open.
Float switch: physical float rises with water → triggers contact
DI to BMS: 1 = water at this level, 0 = below this level
Uses:
High level alarm (overflow)
Low level alarm (pump protection)
Sump pump start/stop
When to Use Which:
| Situation | Level Sensor (Continuous) | Level Switch |
|---|---|---|
| Need exact % level | Yes | No |
| Pump start/stop on level | Yes — with setpoints | Yes |
| Simple overflow alarm | Works | Simpler and cheaper |
| Dashboard display | Yes | Only on/off indication |
| Cost | Higher | Lower |
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