Temperature Measurement · Resistance Temperature Detectors
Stainless steel NTC thermistor probe with a 10 kΩ element at 25°C and a 3950 K B value, supplied with lead wires and plug terminals for control boards and acquisition modules.
An NTC thermistor temperature probe measures temperature through a semiconductor element whose resistance falls as it warms. That behaviour is the opposite of the platinum elements used in process RTDs, and it is why this family is specified by its own pair of numbers rather than by a Pt designation: the resistance at a reference temperature, and the B constant that describes how steeply the resistance changes across the range.
The build on this page is the 10K variant, with a nominal 10 kΩ at 25°C and a B25/50 value of 3950 K, both held to ±1%. The sensing element sits in a 304 stainless steel probe of 5×25 mm, brought out on lead wires and terminated in XH-2P plug connectors so the probe can be plugged straight into a control board or an acquisition module rather than landed on a terminal block.
Because the 25°C resistance and the B constant are both toleranced, the two figures a control board needs in order to linearise the signal are specified rather than nominal. That is the practical difference between a probe that tracks a setpoint in a thermostatic appliance and one that merely switches near it.
A thermistor is a semiconductor whose carrier concentration changes with temperature, and for a negative temperature coefficient element the resistance drops as the element warms. The change is steep compared with a metal element, which is the source of both its strengths and its limits. Over a narrow span around room temperature a thermistor produces a large resistance change for a small temperature change, so a simple circuit can resolve a fine increment. Over a wide span the same curve is strongly non-linear, so the reading has to be linearised against the specific element, which is exactly what the R25 and B pair describe.
That is why two probes with the same nominal resistance are not interchangeable. Two 10 kΩ elements with different B constants follow different curves, and a board linearised for one will read offset from the other across the range even though both agree at 25°C. The material supplied here states the B value for the 10K build only and leaves the other resistance options without one, so those options cannot be treated as the same device with a different reference resistance.
The probe body and how it meets the medium set what the element actually sees. A stainless sheath gives the element mechanical protection and a defined thermal path, and the thermal time constant of 3 seconds measured in stirred water is a property of that assembly rather than of the semiconductor alone: sheath diameter and wall thickness, and how firmly the element sits inside it, matter more than the element type. The same probe in still air is a slower device, and the material states as much by measuring the constant in agitated water.
Self-heating is the second effect to keep in view. The dissipation constant of 3.6 mW/°C is the power that raises the sensing body by 1°C in still air, and the 256 mW maximum power is a destruction limit rather than a working figure. Between them sits the design decision: enough excitation current to resolve the temperature, not so much that the element warms itself. In still air, where heat leaves slowly, that ceiling is much lower than it is in a liquid.
Start from what the reading has to drive. A thermostat, a protection cut-out and a temperature display all place different demands on the same probe, and the two numbers that decide whether a board can use it are the resistance at 25°C and the B constant. Where a board is already built for one pair, changing either the resistance value or the B value changes the displayed temperature, so the probe has to be matched to the input rather than bought to the same nominal value.
Then the temperature span. The two ranges stated in the supplied material do not agree, and the material itself flags the discrepancy, so a hot application should be engineered against the lower figure until that is confirmed. A probe chosen near the top of a range leaves no margin for the tolerance on the element or for the difference between the medium temperature and the temperature at the element.
Then the mechanical fit. The standard probe is 5×25 mm and the material offers other dimensions to order, but probe size is not only a fitting question: a larger sheath responds more slowly, and a smaller one reaches into places a larger one cannot. Where the probe is pressed against a surface rather than immersed, the contact area and the clamping force decide the reading as much as the element does.
Finally the connection. The XH-2P plug suits a board with a mating header. Where the run is long or the environment is wet, the lead length and its insulation have to be settled, and neither is stated in the supplied material.
The element family is the first limitation. This is a thermistor, not a platinum RTD, so it cannot be substituted onto a PT100 input and it cannot be used where a documented, traceable temperature is required without an R-T table and a calibration record. Where the process needs a temperature that can be referred back to a standard, the platinum family is the one to use and this probe is not an equivalent.
The second is that the supplied material gives no resistance-temperature table. The R25 and B pair describes the curve, but a control board is usually linearised against a table rather than against two figures, and several of the reliability tests are stated as a permitted drift on resistance, which can only be converted into a temperature error once that table is available.
Third, the material states no ingress protection rating, no lead length, no lead temperature rating and no certification. Those are published on this page as information required rather than estimated. The dielectric strength and insulation resistance figures were measured in water, which speaks to the electrical isolation of the lead assembly, but they are not a statement about how long the probe may remain immersed or in what media.
Finally, the identification is open. The product carries no model designation in the supplied material, so where an order is placed the resistance value, the B value, the probe dimensions, the lead length and the terminal form all need to be stated rather than quoted as a code.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
| Element | NTC thermistorStandard |
|---|---|
| Zero-power resistance at 25°C | 10 kΩ, tolerance ±1%Standard |
| B constant B25/50 | 3950 K, tolerance ±1%; stated for the 10K build onlyStandard |
| B value of other resistance options | Information requiredInformation required |
| B constant definition | B(T1/T2) = ln(RT1/RT2) / (1/(273.15+T1) - 1/(273.15+T2))Standard |
| Resistance-temperature table | Information requiredInformation required |
| Reference standard behind the tolerance figures | Information requiredInformation required |
| Thermal time constant | 3 s, measured in stirred water between 25 and 50°C as the time to reach 63.2% of the resistance changeStandard |
|---|---|
| Dissipation constant | 3.6 mW/°C, the power that raises the sensing body 1°C in still airStandard |
| Maximum power | 256 mW at 25°C in still airStandard |
| Dielectric strength | AC1800 V applied for 1 second, or AC1500 V for 1 minute, in water at a trip current of 1 mAStandard |
| Insulation resistance | Not less than 100 MΩ measured at DC 500 VStandard |
| Certification | Information requiredInformation required |
| Probe material | 304 stainless steelStandard |
|---|---|
| Probe dimensions | 5×25 mm nominal, custom sizes to orderStandard |
| Terminal form | XH-2P plug terminalsStandard |
| Lead length | Information requiredInformation required |
| Lead temperature rating and insulation material | Information requiredInformation required |
| Ingress protection | Information requiredInformation required |
| Sensor mass and dimensions | Information requiredInformation required |
| High temperature soak | 1000 ±48 h at 100 ±3°C, then 2 h at room temperature; ΔR/R1 ≤3%Standard |
|---|---|
| Low temperature soak | 1000 ±48 h at -30 ±3°C, then 2 h at room temperature; ΔR/R1 ≤3%Standard |
| Damp heat soak | 1000 ±48 h at 60 ±3°C and 90 to 95% relative humidity, then 2 h at room temperature; ΔR/R1 ≤3%Standard |
| Thermal shock | 1000 cycles of 10 min at -30°C and 10 min at 100°C, 2 to 3 min transfer, then 2 h at room temperature; ΔR/R1 ≤3%Standard |
| Lead strength | 50 N along the lead axis for 1 min, then 10 bending cycles of 90°, bending and straightening counted once each; no visible damage and no electrical changeStandard |
| Vibration | The least favourable frequency within 10 to 500 Hz at 0.75 mm amplitude, 2 h in each of the up-down and left-right directions; no visible damage, ΔR/R1 ≤3%Standard |
| Warranty | Information requiredInformation required |
|---|---|
| Test certificate or calibration document | Information requiredInformation required |
| Packaging quantity and gross weight | Information requiredInformation required |
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| 10K, B3950 | R25 = 10 kΩ ±1%, B25/50 = 3950 K ±1% | -30 to 180°C in the parameter table; -20 to 105°C on the main image | The only build for which the B value is stated in the supplied material |
| 5K | R25 = 5 kΩ; B value not stated in the supplied material | Same probe and terminal options as the 10K build | Confirm the B value before pairing with a control board |
| 50K | R25 = 50 kΩ; B value not stated in the supplied material | Same probe and terminal options as the 10K build | Confirm the B value before pairing with a control board |
| 100K | R25 = 100 kΩ; B value not stated in the supplied material | Same probe and terminal options as the 10K build | Confirm the B value before pairing with a control board |
| Custom probe | Probe dimensions and lead arrangement to order | To be agreed against the medium and the response time required | A change of probe size changes the thermal time constant Made to order |
Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.
The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:
No. The resistance of this element falls as it warms, while a platinum RTD rises, so the two cannot share an input without changing how the instrument interprets the signal. A controller set for PT100 will display a reading from this probe, but it will be the wrong one.
The parameter table states -30 to 180°C and the main image states -20 to 105°C. Both are reproduced here as supplied and neither has been chosen for you. Where the application runs hot, treat the lower figure as the limit until the discrepancy is resolved.
It is stated for the 10K build. The 5K, 50K and 100K options are listed without a B value, and the two together decide how the resistance maps to temperature, so a control board must be matched to both figures of the specific build ordered.
The 3 second thermal time constant was measured in stirred water between 25 and 50°C. In still air or in a medium that is not agitated the probe responds noticeably more slowly, so the same probe should not be expected to track a fast-changing temperature outside a well-mixed liquid.
It is the power that warms the sensing body by 1°C in still air, and it is a different figure from the 256 mW maximum power. The excitation current should be kept low enough that self-heating stays small against the accuracy the application needs, which matters most where the probe is in air rather than immersed.
The material states the tip is a 304 stainless steel probe and that the dielectric strength and insulation resistance are tested in water, but no ingress protection rating is given. Treat continuous immersion, and any chemically aggressive medium, as something to confirm rather than assume.
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