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  • New item   Duct temperature sensor | PT100 | 100 Ω at 0 °C | IEC 60751
    New item   Duct temperature sensor | PT100 | 100 Ω at 0 °C | IEC 60751 1

    Duct temperature sensor | PT100 | 100 Ω at 0 °C | IEC 60751

    Code: PT100
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    Passive PT100 sensor for measuring air temperature in ventilation and air-conditioning ducts. Standard IEC 60751 characteristic – connects to a controller, PLC RTD input or via a 4–20 mA converter.

  • Product description

    Duct temperature sensor PT100 – for measuring air temperature in ducts

    The PT100 duct sensor is installed in a ventilation or air-conditioning duct and measures the temperature of the passing air. It is a passive resistive element: its resistance changes with temperature, and the value is read by a controller, thermostat or signal converter. PT100 is a platinum resistance element with 100 Ω at 0 °C (IEC 60751). Before ordering, make sure your controller input supports PT100 specifically.

    Key point:
    PT100 is the most widespread resistance sensor in industry, with a standardised characteristic, so it is supported by most controllers, PLC analogue modules and converters. It stays stable over time and suits applications that need accurate, repeatable measurement. Because the base resistance is low (100 Ω), the wiring scheme matters – for long cables, 3- or 4-wire connection or a 4–20 mA converter is better.
    Sensing element
    PT100
    Resistance at 0 °C
    100 Ω
    Resistance at 100 °C
    138.5 Ω
    Mounting
    in duct

    Operating principle

    In a resistance temperature detector (RTD) the resistance of the metal rises as temperature rises. The PT100 element has 100 Ω at 0 °C and 138.5 Ω at 100 °C. The controller passes a small measuring current through the element, measures the voltage drop and converts it into temperature.

    The PT100 resistance changes by about 0.385 Ω per degree. That is why lead resistance adds directly to the result: in a 2-wire connection, every additional 1 Ω of lead resistance raises the reading by about 2.6 °C. 3- and 4-wire schemes compensate for this error.

    The probe of a duct sensor is inserted through the duct wall so that the sensing part sits in the air stream. The reading reflects the supply, extract or outdoor air temperature at the point where the probe is installed.

    Why use a PT100 duct sensor?
    A PT100 duct sensor fits where the air handling unit is controlled by an industrial controller or a PLC with an RTD input. The standard IEC 60751 characteristic lets you swap sensors between manufacturers without changing controller settings, and with a 4–20 mA converter the signal can be transmitted over long distances.

    Technical specifications

    Product type Duct temperature sensor, passive
    Manufacturer / model Manufacturer not specified / PT100
    Sensing element PT100 (platinum)
    Resistance at 0 °C 100 Ω
    Resistance at 100 °C 138.5 Ω
    Characteristic IEC 60751 (α = 0.00385 1/K)
    Sensitivity (average 0–100 °C) ≈ 0.385 Ω/K
    Output signal Resistance (passive, no power supply)
    Measuring range, IP, probe length, number of wires Check for the specific batch – contact our sales manager

    Main functions

    • Duct air temperature measurement – monitoring of supply, extract or outdoor air in an air handling unit
    • Passive resistive signal – no separate power supply, connects directly to the controller input
    • Standard IEC 60751 characteristic – compatible with most PLC RTD modules and converters
    • 4–20 mA transmission option – with a PT100 converter the signal runs over long cables without lead resistance effects
    • Feedback for control – the controller adjusts heating, cooling or heat recovery output based on the reading
    • Protection logic – the reading is used, e.g., in heater frost or overheat protection functions in the controller

    How does it differ from similar products?

    NTC sensor (e.g. 10 kΩ) NTC resistance falls as temperature rises and changes non-linearly; PT100 resistance rises almost linearly and is standardised by IEC 60751.
    PT1000 The same platinum element but 1000 Ω at 0 °C – lead resistance has a 10 times smaller effect. PT100 is more common in industrial PLCs and converters.
    Active 4–20 mA / 0–10 V sensor An active sensor has a built-in transmitter and needs power; PT100 is passive, its signal is read by an RTD input or converter.

    Where is it used?

    • Supply air ducts of air handling units
    • Extract air ducts
    • Outdoor air intake ducts
    • Air-conditioning systems (AHU)
    • Building automation (BMS) systems
    • Industrial ventilation and drying systems

    Use by need

    For beginners.
    The key point is that the sensor type must match the controller setting. If PT100 is selected in the controller, this sensor fits; a sensor of a different type will show the wrong temperature.
    For experienced installers.
    Consider the cable length: in a 2-wire PT100 connection, 1 Ω of lead resistance gives an error of about 2.6 °C. For longer lines use 3- or 4-wire connection (if the sensor has it) or a PT100 → 4–20 mA converter next to the sensor; some controllers allow lead resistance correction.
    For energy engineers / designers.
    In the design, specify the element type (PT100), characteristic, accuracy class, wiring scheme and probe length for the duct size. Place the sensor in a straight duct section, away from the heater or fan.

    Practical application

    The supply air temperature of an air handling unit is controlled by a PLC with a PT100 input, and the sensor is 40 m away from the panel. To keep lead resistance from distorting the reading, a PT100 → 4–20 mA converter is installed next to the duct, and a current signal, immune to lead resistance and less sensitive to interference, is sent to the panel.

    Pros / advantages

    • Passive – no power supply needed
    • Standard characteristic – easy to configure in the controller
    • Simple connection to a resistance input
    • Stable, almost linear characteristic
    • Suitable for ventilation in residential, commercial and industrial buildings

    Cons / limitations

    • Works only with a controller that supports a PT100 input
    • Low base resistance – in 2-wire connection the resistance of long leads causes a noticeable error
    • Exact dimensions, IP and range for this batch are not confirmed – check before ordering

    Safety and installation notes

    • ⚡ The sensor is connected to a controller or panel that may contain 230 V AC circuits – disconnect the power before work; panel work must be done by a qualified electrician.
    • Route the signal cable separately from power cables and frequency converter lines to reduce interference.
    • Seal the duct opening around the probe so that no air is drawn in and no condensation forms.
    • Do not install directly after a heater or next to a fan – the air there is not mixed and the reading will be inaccurate.

    Quick selection guide

    PT100
    100 Ω at 0 °C
    Duct
    Passive signal
    Suitable when you need:
    • To replace an existing duct sensor of the same type (PT100)
    • To measure supply or extract air temperature
    • To connect to a PLC RTD module or a PT100 → 4–20 mA converter
    Check before choosing:
    • Whether the controller input is configured for PT100
    • Cable length and wiring scheme (2, 3 or 4 wires)
    • Probe length for the duct diameter and mounting point
    Important reminder: PT100 is not universal – with a controller set for NTC, PT1000 or Ni1000 it will read incorrectly. The sensor only measures: control is done by the controller.
    ☝ Elsprendimai.eu recommends:

    FAQ

    Does this sensor need a power supply?
    No. It is a passive resistive element – the measuring current is supplied by the controller input.
    Can I replace PT100 with an NTC sensor?
    No. The resistance and characteristic curve differ, so the controller will show the wrong temperature. The sensor type must match the controller setting.
    How do I check that the sensor works?
    Disconnect it from the controller and measure the resistance with a multimeter. At 0 °C it should be about 100 Ω, at room temperature slightly higher.
    Where in the duct should the sensor be installed?
    In a straight section where the air is well mixed – not directly after a heater, cooler or fan.
    How many wires does a PT100 need?
    It depends on the sensor and controller: 2-wire connection is the simplest, but lead resistance adds to the reading; 3- and 4-wire schemes compensate for it. Check the number of sensor wires before ordering.
    Can a PT100 be connected to a 4–20 mA input?
    Not directly. You need a PT100 → 4–20 mA converter that turns the resistance into a current signal.

    Sources: Element characteristic – IEC 60751 (PT100: 100 Ω at 0 °C, α = 0.00385 1/K). No datasheet from a specific manufacturer was found, so dimensions, IP and range are not stated. Checked 2026-10-18.

    PT100 duct temperature sensor

    The PT100 duct temperature sensor measures air temperature in ventilation and air-conditioning ducts. The platinum element (100 Ω at 0 °C, IEC 60751) connects to a controller or PLC RTD input or via a 4–20 mA converter.

    Illustrative image may have been created using AI. The appearance of the product may differ slightly from the image shown. Please refer to the technical specification.

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