HVAC and fluid probes
Define the fluid, sealing and response requirement before selecting a sheath.
GUILCOR · PTC sensing and selection
KTY81-110
Account for the leads.
A silicon PTC for temperature measurement. Match the controller curve, then check how the cable contributes to the reading.
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Sensor selection
Understand KTY81-110.
1 kΩReference resistance at 25 °C
±1%R25 selection tolerance
SOD70Plastic, two in-line leads
KTY81-110 identifies the 1 kΩ selection of the KTY81 family. It is a continuously varying sensor, so its job is to provide a temperature-dependent resistance to a measuring circuit. It does not switch a motor load by itself.
Selection context
From sensor resistance to a temperature reading.
Keep the sensor characteristic and the controller configuration together. The diagram shows the measurement path; the circuit must account for the complete sensing assembly.
Reference point
1 kΩat 25 °C
Sensor→Readout→Temperature
Characteristic and construction
The reference details that matter.
The reference datasheet gives 990–1010 Ω at 25 °C with 1 mA test current and a −55 to +150 °C ambient range. The SOD70 body is plastic with two leads on the same side. These element limits do not establish the rating of a completed probe.
Reference documents: NXP KTY81 reference datasheet. Confirm the documentation for the supplied part.
| Reference point | R25 = 1000 Ω |
|---|---|
| Controller characteristic | KTY81/110, not Pt1000 |
| Connection | Two-terminal element; account for the cable loop |
| Accuracy | R25 tolerance and curve tolerance are separate contributions |
A practical application check
How much error comes from the cable?
Tool input range: 0 to 100
Tool input range: 0.01 to 20
Enter the resistance of one lead and an allowable cable contribution. This estimate uses the local sensitivity near 25 °C to show why even a small series resistance can matter.
Total lead resistance
Approximate offset at 25 °C
Enable JavaScript to calculate.
Local estimate at 25 °C only. It excludes sensor tolerance, cable temperature changes, ADC error and self-heating.
Calculation or decision ruleRloop = 2 × Rlead; ΔT ≈ Rloop / 7.9 Ω/K
Measure the complete cable loop or derive it from the specified conductor and length. A calibration offset at one temperature cannot establish accuracy over the full operating interval.
Wiring and self-heating
Connect the circuit and control the heat.
Connect the identified reference
Use a controller configured for the KTY81/110 characteristic. A resistance divider or controlled measuring current can provide an ADC signal. Additional cable conductors only compensate lead resistance when the readout circuit explicitly supports that arrangement.
Sensing element → measurement input → temperature evaluation
Control self-heating and installation effects
Electrical measurement adds heat: P = I²R. A first estimate of the steady-state temperature rise is P/δ, provided the dissipation factor δ describes the actual mounting. The current that produces a convenient voltage is not automatically suitable for the required accuracy.
Mechanical contact, insulation, sheath mass and nearby heat sources influence the temperature followed by the element. Evaluate the finished assembly in the intended medium and mounting.
Operating principle
Match the principle to the application.
How the signal is used
For a resistance sensor, the readout converts the measured electrical signal using the selected R/T characteristic. A nominal reference value is one point on that curve. Use the manufacturer’s table or valid coefficients for the interval of interest; a constant slope is only a local approximation.
Strengths and selection limits
A resistance output is convenient for a simple analogue front end. The tradeoff is that wiring, reference-resistor tolerance and current-induced heating become part of the temperature error budget. A nominal 1 kΩ at 25 °C does not make this a Pt1000, whose reference point and curve are different.
Application contexts
Where to evaluate KTY81-110.
Equipment monitoring
Keep the sensing point thermally coupled to the surface being monitored.
Existing controller service
Identify the programmed curve before changing the element or cable.
Engineering example
Turn a resistance into a usable signal.
These typical reference points describe the named NXP selection under its stated measuring conditions. They are not tolerance limits or calibration results for an assembled probe.
| Temperature (°C) | Typical resistance (Ω) |
|---|---|
| 0 | 815 |
| 25 | 1000 |
| 100 | 1696 |
The reference table uses 1 mA measuring current. For temperatures between points, use the complete manufacturer table or a validated fit; do not extrapolate beyond its specified interval.
KTY81 manufacturer characteristic
Controlled-current readout
Current source → sensor → return; measure voltage across the sensor with a suitable ADC input. For an ideal 1 mA current and 1000 Ω at 25 °C, V = I × R = 1.000 V and P = I² × R = 1.000 mW. Current-source accuracy, input offset and lead resistance must be included in the measurement budget.
For two leads of 1 Ω each, the input sees an additional 2 Ω. Using the local 25 °C sensitivity of 7.9 Ω/K gives approximately 0.25 °C of positive offset. This local estimate does not replace the full characteristic or account for the sensor’s own tolerance.
Before requesting a reference
Specify the complete assembly.
Electrical and thermal information
- Manufacturer, complete part number and source document.
- Required measurement range or response temperature.
- Curve and tolerance, or resistance limits around the switching region.
- Controller reference, measuring conditions and required accuracy or detection behaviour.
- Response requirement in the actual medium and installation.
Mechanical and project information
- Mounting position, dimensions, sheath or board layout.
- Cable, connector, pin assignment and electrical insulation.
- Media, vibration, moisture and temperature exposure.
- Calibration or functional test requirements for the final assembly.
- Expected quantity, traceability and replacement constraints.
Probe construction
Choose the installation format.
Explore the probe constructions below, then confirm feasibility for the selected element. A construction link does not imply that every PTC reference is available in that format.
Frequently asked questions
KTY81-110 questions.
Can I remove cable error with a three-wire cable?
Only with a suitable three-wire measurement circuit. Adding a wire to a two-terminal input does not automatically compensate the cable.
Does the bare-element rating apply to the whole probe?
No. Cable, joints, insulation, sealing and mounting can set a lower limit. Specify and validate the completed assembly.
Can the application check replace a product specification?
No. Each check uses the assumptions shown beside it. Confirm the exact sensor and controller documents and test the finished application.
What should I send to GUILCOR?
Send the full part reference if known, controller details, temperature requirement, installation drawing, cable and connector requirements, and expected quantity.
SELECTION / YOUR APPLICATION
Is KTY81-110 the right starting point?
Match the reference to the application.
The equipment specifies the KTY81-110 continuous resistance characteristic. Match the readout configuration and complete sensing assembly.
Review the specification →Review KTY81-210 alongside KTY81-110.
Confirm the intended electrical function first: continuous measurement, temperature protection or another circuit role. Compare the exact manufacturer characteristic and operating conditions.
Explore KTY81-210 →Keep the complete specification together.
Use the full manufacturer reference and suffix. Confirm the circuit role, resistance characteristic, package and readout or protection circuit before considering a substitute.
Prepare your enquiry →These links support a specification review. They do not establish interchangeable parts or availability of a complete assembly.
More selection details
Compare the sensing principle and exact reference before considering a substitution.
GUILCOR / YOUR ENQUIRY
Define your KTY81-110 enquiry.
State what the PTC must do in the circuit. The category name alone does not define a measurement curve, a switching threshold or a compatible replacement.
Missing a reference or datasheet?
Send the component marking, equipment reference and any photographs or documents you have. These provide a starting point for identifying what must be confirmed.
The outline helps prepare your enquiry. Copying it does not send a request.
FOUR DETAILS THAT MOVE THE DISCUSSION FORWARD
01
Device and circuit function
Full manufacturer part number and suffix, measurement or protection function, resistance characteristic or response threshold, tolerance and connected circuit.
02
Measurement conditions
Normal and peak temperatures, required measurement or protection behaviour, thermal contact, response needs and reset conditions where applicable.
03
Assembly and connection
Package or sensing assembly, mounting, insulation, lead or cable arrangement, connector and any exposure to vibration, moisture or cleaning.
04
Project and validation
Sample and production quantities, target delivery, calibration or documentation needs, and the checks required before approval.