Maintenance teams
Record the hidden element reference alongside the probe assembly drawing.
GUILCOR · PTC sensing and selection
Sillistor
Identify the curve first.
The Sillistor category brings together silicon PTC selection questions. Start with a complete reference instead of assuming one nominal resistance for the whole family.
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Sensor selection
Understand Sillistor.
Silicon PTCTemperature-dependent resistance
Full referenceNeeded to identify the curve
Curve matchingRequired before substitution
A silicon PTC used for measurement has a rising resistance characteristic over its specified sensing range. The category name alone does not define R25, package, tolerance or operating limits. A replacement must match the circuit as well as the installation.
Selection context
Three parts of a replacement specification.
Identify the component, its resistance characteristic and the finished assembly before assessing a replacement. Use the checklist below to track the information you have confirmed.
Specify the complete sensor
Part.Curve.
Assembly.
One resistance measurement is only one point.
Characteristic and construction
The reference details that matter.
KTY81, KTY83 and KTY84 illustrate why a silicon PTC cannot be specified by the word “PTC” alone: their reference points and packages differ. Use the actual manufacturer curve and measuring conditions rather than applying one quadratic equation to every silicon sensor.
Reference documents: NXP KTY81: a silicon sensing family · NXP KTY84: a different reference-temperature example. Confirm the documentation for the supplied part.
| Nominal resistance | State the value and its reference temperature |
|---|---|
| Curve | Specify the actual family and selection |
| Readout | Check current, divider, input range and pinning |
| Assembly | Specify mounting, leads, insulation and sealing |
A practical application check
Check the replacement information.
Mark which items have been verified for the proposed replacement. The checklist exposes missing information; completion is a document review milestone, not an interchangeability certificate.
Items confirmed
Items still to verify
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A room-temperature resistance measurement cannot establish curve compatibility over the operating range.
Calculation or decision ruleReview the identified part, characteristic, input and finished assembly together.
Ask for the original part marking, controller manual and application temperature range. Retain the source of each confirmed item so the next replacement does not depend on a visual guess.
Wiring and self-heating
Connect the circuit and control the heat.
Connect the identified reference
Determine whether the manufacturer specifies anode/cathode orientation or interchangeable electrical contacts. Connect according to that reference and the controller manual. A two-terminal silicon element is not automatically compatible with a platinum RTD input.
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 familiar name can make maintenance requests easier, but it is not a complete purchasing specification. Retaining the full reference and controller configuration is especially useful when the mechanical probe hides the original element marking.
Application contexts
Where to evaluate Sillistor.
Controller migration
Confirm the new input supports the required curve and excitation.
Custom probes
Choose the sensing characteristic before defining the sheath and connector.
Engineering example
Compare identified curves before calculating temperature.
The category name does not identify one set of coefficients. The examples below show why the nominal resistance, its reference temperature and the complete part number must travel together.
| Example reference | Nominal reference point | Typical resistance at 100 °C |
|---|---|---|
| KTY81-110 | 1000 Ω at 25 °C | 1696 Ω |
| KTY81-210 | 2000 Ω at 25 °C | 3392 Ω |
| KTY84-130 | 1000 Ω at 100 °C | 1000 Ω |
Example readout circuit
Supply → fixed resistor Rs → ADC node → identified sensor → ground. In the ideal unloaded circuit, Vout = Vs × R / (Rs + R), and R = Rs × Vout / (Vs − Vout). For an assumed 3.3 V supply, 2000 Ω fixed resistor and 2000 Ω sensor, Vout is 1.650 V. The current is 0.825 mA and sensor dissipation is approximately 1.361 mW.
From resistance to temperature
After converting voltage to resistance, use the table for the identified part. For example, KTY81-210 has typical values of 2785 Ω at 70 °C and 2980 Ω at 80 °C. Linear interpolation of 2800 Ω between those points gives approximately 70.77 °C. This is a local estimate between typical points, not a guaranteed temperature measurement.
A quadratic fit can also be used when its coefficients, units and validity interval are documented. Do not apply one silicon sensor’s fit to every Sillistor. A percentage resistance tolerance is not a universal temperature accuracy class; convert it through the local slope and add circuit, lead and installation errors.
Integration checks
Choose the excitation and fixed resistor from the complete range, not only the room-temperature value. Verify ADC input loading and settling after any filter, reference stability, open/short detection and self-heating. Calibration at known temperatures can identify offsets, but does not by itself prove the curve between or beyond those points.
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
Sillistor questions.
Is every Sillistor a 2 kΩ sensor?
No universal 2 kΩ value is implied here. Specify the full reference, resistance and reference temperature.
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 Sillistor the right starting point?
Match the reference to the application.
You need to identify a silicon PTC measurement element. Obtain its full reference, curve and package before specifying the readout or replacement.
Review the specification →Review TFPT alongside Sillistor.
Confirm the intended electrical function first: continuous measurement, temperature protection or another circuit role. Compare the exact manufacturer characteristic and operating conditions.
Explore TFPT →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 Sillistor 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.