Pt1000 3-wire connection

In greenhouses, Pt1000 is often used for air temperature, stem temperature, and soil temperature. The 3-wire circuit compensates for cable resistance.

Terminals on a Priva / Hoogendoorn module

sensor       module
─────        ───────
 A ──────── A (current source +)
 B ──┬───── B (sense)
     │
 C ──┴───── C (current return / GND)

A-B is the measuring resistor; B-C is an identical cable that the module uses to subtract the cable resistance.

Common mistakes

1. A and C swapped — module reads drastically incorrect temperature (often -200 °C).
2. B not connected — no compensation, drift of +1 to +2 °C per 100 m of cable.
3. Common C between multiple sensors — not allowed, causes crosstalk.
4. Shield not grounded on one side only — 50 Hz hum on the signal.

Recommended cable

• LiYCY 3×0.25 mm², shielded, shield grounded on the module side.
• Maximum 100 m for 0.25 mm²; use 0.5 mm² above that.