Temperature sensor selection depends on the temperature range, accuracy needed, response time, and the media and environment around the sensing element. RTDs and thermocouples each have strengths; the wrong choice gives reliable readings that are simply not accurate.
Specs to confirm before ordering:
- Sensor element: Pt100 (most common RTD), Pt1000, Type K thermocouple (broad range), Type J (legacy), Type T (cryogenic), Type N (oxidation resistance)
- Temperature range — RTDs typically -200 to 600 °C; thermocouples extend to 1700 °C+ depending on type
- Accuracy class: RTD Class A (±0.15 °C at 0 °C), Class B (±0.3 °C); thermocouple Special Limits or Standard Limits
- Wiring: 2-wire (lead resistance error), 3-wire (most common for RTDs), 4-wire (highest accuracy)
- Probe sheath material: 316 stainless, Inconel (high-temp), PTFE (corrosion)
- Probe diameter and immersion length
- Process connection: 1/2" NPT, G1/2, sanitary tri-clamp, spring-loaded bayonet
- Output: direct sensor signal (Pt100 mV/Ω, TC mV) or integrated transmitter (4–20 mA, HART, IO-Link)
For PLC interfacing, RTDs with a head-mounted 4–20 mA transmitter avoid the need for a dedicated RTD input card and reduce wiring error from long lead lengths. Direct RTD wiring is fine for short runs and a proper RTD input module. Thermocouples need cold-junction compensation handled either at the PLC or at a transmitter — and the extension wire must match the thermocouple type (Type K extension wire for a Type K probe, etc.). Mixing copper wire on a TC produces a free second junction and a baseline offset.
Typical applications: extruder barrel zone control, oven setpoint feedback, bearing-temperature monitoring on large motors, and tank media temperature in food and chemical processing. For legacy machines, OEM probe geometry (sheath length, well fit) is what determines whether a replacement physically fits — that is usually the binding constraint, not the electrical spec.
Request a quote for any obsolete temperature probe or transmitter.
