Engineering notes
BMS sensors: choose 0–10 V or 4–20 mA
When to use 0–10 V and when to use 4–20 mA on BMS sensors. Cable length, noise, controller input.
Two common analog standards
BMS sensors usually output 0–10 V or 4–20 mA. Both work if the controller input matches. The wrong input reads zero or full scale — the software still “has a point” and control is wrong.
When 0–10 V is enough
- Short runs on the same floor, same technical cupboard
- AHU valves and air sensors close to the DDC
- The panel already has voltage inputs and enough 24 V
Voltage drops on long cable and picks up noise near drives. Do not run 0–10 V beside power cable for tens of metres without a noise method.
When 4–20 mA is the better default
- Long runs: workshops, shafts, plant far from the panel
- Noise: next to drives, welders, busbars
- You need a broken-wire alarm: current falls below 4 mA — clearer than 0 V
Some DDC inputs are voltage only. Then the schedule must name the burden resistor from the maker’s manual. Choosing sensors · NTC, PT100, PT1000