PT100 Temperature Probes

Why PT100 and not a generic sensor

PT100 probes (platinum RTDs) are the industrial standard for process temperature thanks to their stability and accuracy (±0.1°C), well above a type-K thermocouple below 300°C. The iGromi Bridge reads them natively, with no intermediate transmitter.

Step 1: Choose the wiring configuration

There are three physical variants — check how many wires your probe has:

• 2-wire: The simplest, but the cable's own resistance adds to the reading error. Only recommended for runs under 3 metres.
• 3-wire: The industrial standard. Automatically compensates for cable resistance. Use it whenever possible.
• 4-wire: Laboratory-grade accuracy, eliminating cable error entirely. Rare on the plant floor.

Step 2: Wiring to the iGromi Bridge

The Bridge's RTD input module accepts all three configurations:

1. For 3-wire: connect the two same-coloured wires to terminals RTD-A and RTD-B, and the third to RTD-C.
2. Route the probe cable away from power cabling and variable frequency drives — they induce noise into the reading.
3. Avoid tight metal cable ties over the probe cable; they can induce parasitic resistance.

Step 3: Software configuration

1. In Edge Devices > RTD Input, select the probe type (PT100) and the wiring configuration (2/3/4 wire).
2. Define the alarm range (e.g. warn at 80°C, trip at 95°C for a motor).
3. iGromi OS applies the Callendar-Van Dusen conversion curve automatically — there is no need to compute resistance-to-temperature by hand.

Quick sanity check

At room temperature (~25°C) a PT100 should read approximately 109.7Ω. If the dashboard value is far from that, check the wire configuration before suspecting the probe.