The Fluke Calibration 5618B is a high-precision industrial resistance temperature detector (RTD) designed for demanding temperature measurements, reference thermometry and professional temperature calibration applications.
With a temperature measurement range from −200 °C to +500 °C, a slim stainless steel probe diameter of 3.2 mm and an individually accredited calibration with ITS-90 coefficients, the Fluke Calibration 5618B combines excellent metrological performance with a compact and practical design.
The instrument belongs to the Fluke Calibration family of small-diameter industrial platinum resistance thermometers (PRTs). It provides secondary reference-level performance and is particularly suitable for applications requiring precise temperature measurements with limited immersion depth.
Its small probe diameter reduces heat conduction between the measurement environment and the sensing element. This helps minimize immersion errors, particularly when measuring temperature in compact calibration wells or small measurement openings.
The Fluke Calibration 5618B is available in three probe lengths: 152 mm, 229 mm and 305 mm. Depending on the selected version, it covers temperatures up to 300 °C or 500 °C.
Each probe is supplied with an accredited calibration certificate containing individual ITS-90 coefficients and resistance-versus-temperature values.
For professional calibration and metrological traceability, visit the europascal Calibration Service.
Your Benefits at a Glance
- Temperature measurement range from −200 °C to +500 °C
- Short 152 mm version available for temperatures up to 300 °C
- Secondary reference-level temperature measurement performance
- Small probe diameter of only 3.2 mm
- High-quality stainless steel 316 probe sheath
- Nominal resistance of 100 Ω at 0 °C
- Nominal temperature coefficient of 0.003923 Ω/Ω/°C
- Excellent temperature measurement repeatability
- Low hysteresis
- Fast response to temperature changes
- Reduced immersion errors due to slim probe construction
- Three probe lengths available
- Accredited manufacturer calibration included
- Individual ITS-90 calibration coefficients
- Resistance-temperature calibration table
- Suitable for precision thermometer readouts
- Compatible with several Fluke Calibration thermometer instruments
- Different electrical termination options
- Suitable for liquid calibration baths
- Suitable for dry block calibrators
- Suitable for infrared calibrator verification
- Professional calibration support from europascal
Wide Temperature Range from −200 °C to +500 °C
The Fluke Calibration 5618B provides a wide temperature measurement range.
For the 229 mm and 305 mm versions, the specified temperature range is:
−200 °C to +500 °C
The shorter 152 mm version provides a temperature range of:
−200 °C to +300 °C
This makes the Fluke Calibration 5618B suitable for a wide variety of laboratory and industrial temperature measurement applications.
The lower temperature limit allows measurements in cryogenic environments and low-temperature calibration systems.
The upper temperature limit of 500 °C makes the longer probes suitable for industrial temperature calibration and high-temperature comparison measurements.
The appropriate probe length should be selected according to the required temperature range, immersion depth and mechanical installation conditions.
Small Probe Diameter of 3.2 mm
One of the most important characteristics of the Fluke Calibration 5618B is its slim probe construction.
The stainless steel sheath has a diameter of:
3.2 mm (0.125 inches)
This small diameter provides several advantages.
The probe can be inserted into narrow calibration wells and small measurement openings.
Its reduced thermal mass also supports a relatively fast response to temperature changes.
Another important advantage is reduced heat conduction along the probe stem.
This can help minimize immersion errors, particularly when the available immersion depth is limited.
For demanding reference measurements, the influence of immersion depth must nevertheless be evaluated.
Three Available Probe Lengths
The Fluke Calibration 5618B is available in three mechanical configurations.
Fluke Calibration 5618B-6
The 5618B-6 features a probe length of:
152 mm (6 inches)
Temperature range:
−200 °C to +300 °C
This compact version is suitable for applications where installation space is limited.
Fluke Calibration 5618B-9
The 5618B-9 features a probe length of:
229 mm (9 inches)
Temperature range:
−200 °C to +500 °C
This version provides a good balance between compact dimensions and sufficient immersion depth.
Fluke Calibration 5618B-12
The 5618B-12 features a probe length of:
305 mm (12 inches)
Temperature range:
−200 °C to +500 °C
The longer probe is particularly useful when greater immersion depth is required to minimize heat conduction errors.
All three versions have a nominal sheath diameter of 3.2 mm.
Platinum Resistance Temperature Sensor
The Fluke Calibration 5618B uses a precision platinum resistance sensing element.
Platinum resistance thermometers are widely used in temperature metrology because of their excellent stability, repeatability and predictable resistance-temperature relationship.
The nominal resistance of the Fluke Calibration 5618B is:
100 Ω at 0 °C
The nominal temperature coefficient is:
0.003923 Ω/Ω/°C
This coefficient differs from the commonly used industrial Pt100 characteristic with a nominal coefficient of 0.00385 Ω/Ω/°C.
For accurate measurements, the individual ITS-90 calibration coefficients supplied with the probe should be used.
Applying an incorrect sensor characteristic can introduce significant temperature measurement errors.
Accredited ITS-90 Calibration Included
Each Fluke Calibration 5618B is supplied with an accredited manufacturer calibration.
The calibration documentation includes:
- Individual ITS-90 calibration coefficients
- Resistance-versus-temperature values
- Calibration measurement results
- Metrological traceability information
The resistance-temperature table provides values in:
1 °C increments
The individual calibration coefficients allow the probe to be used with compatible precision thermometer readouts.
This is particularly important when the Fluke Calibration 5618B is used as a reference thermometer for comparison calibration.
Calibrated Accuracy
The manufacturer provides calibrated accuracy specifications that include calibration uncertainty and the specified drift contribution.
Representative values are:
| Temperature | Calibrated Accuracy (k = 2) |
|---|---|
| −200 °C | ±0.026 °C |
| 0 °C | ±0.066 °C |
| +500 °C | ±0.219 °C |
These values describe the manufacturer’s specified calibrated performance under the stated conditions.
They should not be confused with the calibration uncertainty alone.
When the probe is used as a reference thermometer, the uncertainty stated on its individual calibration certificate should be considered.
The connected thermometer readout introduces additional measurement uncertainty.
Calibration Uncertainty
The manufacturer provides representative expanded calibration uncertainties for the Fluke Calibration 5618B.
| Calibration Temperature | Expanded Uncertainty (k = 2) |
|---|---|
| −196 °C | 0.024 °C |
| −38 °C | 0.011 °C |
| 0 °C | 0.010 °C |
| +200 °C | 0.018 °C |
| +420 °C | 0.029 °C |
For the shorter 5618B-6 version, the upper calibration point is 300 °C instead of 420 °C.
Actual calibration uncertainties depend on the calibration laboratory and the measurement procedure.
The values stated on the individual calibration certificate are authoritative for the specific probe.
Excellent Temperature Stability
Long-term stability is an important characteristic of reference temperature sensors.
The Fluke Calibration 5618B provides stable measurement performance across a wide temperature range.
The manufacturer specifies a drift contribution of:
±0.1 °C after exposure to the maximum operating temperature under the specified conditions
Regular calibration is recommended to verify the long-term performance of the probe.
Mechanical stress, excessive temperatures and improper handling can influence the resistance characteristics of a platinum resistance thermometer.
Low Temperature Hysteresis
The Fluke Calibration 5618B provides low temperature hysteresis.
The manufacturer specifies hysteresis of less than:
0.01 °C at 0 °C
when using −196 °C and +420 °C as the temperature cycle endpoints.
Low hysteresis is particularly useful for reference measurements involving repeated heating and cooling cycles.
The hysteresis of an individual probe can depend on its thermal history and operating conditions.
Fast Response Time
The small diameter of the Fluke Calibration 5618B provides a relatively fast thermal response.
The manufacturer specifies a time constant of up to:
4 seconds
for a 63.2% response to a temperature step in moving water under the specified test conditions.
Actual response time depends on the measurement medium, flow conditions, immersion depth and thermal contact.
The slim construction makes the probe particularly suitable for applications where temperature changes must be detected quickly.
Stainless Steel 316 Probe Sheath
The Fluke Calibration 5618B features a stainless steel 316 sheath.
This material provides good mechanical strength and corrosion resistance for many industrial and laboratory applications.
The probe is suitable for use in compatible calibration liquids and measurement environments.
The chemical compatibility of the sheath material should be checked before use in aggressive media.
The probe should also be protected against excessive mechanical stress and bending.
Flexible Connecting Cable
The Fluke Calibration 5618B is equipped with a connecting cable approximately:
1.83 m (6 feet)
long.
The cable uses 22 AWG conductors with PTFE insulation.
The cable allows the probe to be connected conveniently to a suitable precision thermometer readout.
The temperature limitations of the cable and transition junction must be observed.
The transition junction has a specified temperature range of:
−50 °C to +200 °C
Exposure outside this range can permanently damage the probe assembly.
Compatible Thermometer Readouts
The Fluke Calibration 5618B requires a suitable precision thermometer readout.
Recommended Fluke Calibration instruments include:
- Fluke Calibration 1523
- Fluke Calibration 1524
- Fluke Calibration 1502A
- Fluke Calibration 1529
- Fluke Calibration 1560
The selected thermometer must support the probe’s resistance characteristic and calibration coefficients.
Using the individual ITS-90 coefficients is recommended for demanding reference measurements.
Electrical Termination Options
The Fluke Calibration 5618B is available with different electrical termination options.
Available configurations include:
- INFO-CON for compatible 914X instruments
- Bare wires
- Five-pin DIN connector
- Gold-plated pins
- Banana plugs
- Miniature spade lugs
- Miniature banana plugs
- INFO-CON for 1523 and 1524
- Spade lugs
The appropriate connector must be specified when ordering.
The selected termination should match the intended thermometer readout.
Reference Measurements in Calibration Baths
The Fluke Calibration 5618B is particularly suitable for precision temperature measurements in liquid calibration baths.
The slim probe can be positioned close to the device under test.
This is advantageous for comparison calibration because temperature differences between the reference and test sensor should be minimized.
The small diameter also reduces the space required within the calibration bath.
For accurate measurements, sufficient immersion depth and thermal stabilization are essential.
The measurement uncertainty should include contributions from the reference probe, thermometer readout, bath stability and temperature uniformity.
Measurements in Dry Block Calibrators
The Fluke Calibration 5618B can also be used in suitable dry block temperature calibrators.
The probe should be inserted into a correctly sized calibration insert.
Good thermal contact between the probe and insert is important for minimizing measurement errors.
The small diameter of the Fluke Calibration 5618B makes it suitable for narrow calibration wells.
For demanding applications, axial temperature gradients, radial uniformity and loading effects should be considered.
Calibration of Infrared Blackbody Sources
An important application of the Fluke Calibration 5618B is the calibration of suitable infrared blackbody temperature sources.
Fluke Calibration specifically recommends the probe for use with the:
Fluke Calibration 9132
and
Fluke Calibration 9133
infrared calibrators.
These temperature sources are designed to allow temperature verification using an appropriate contact reference probe.
The Fluke Calibration 5618B can therefore be used to measure the temperature of the relevant reference location within the calibrator.
This supports traceable verification of the temperature source.
The measurement procedure must follow the manufacturer’s instructions for the respective infrared calibrator.
Technical Highlights
| Specification | Fluke Calibration 5618B |
|---|---|
| Manufacturer | Fluke Calibration |
| Model | 5618B |
| Product type | Industrial Reference RTD Probe |
| Sensor technology | Platinum resistance thermometer |
| Temperature range, 9 and 12 inch versions | −200 °C to +500 °C |
| Temperature range, 6 inch version | −200 °C to +300 °C |
| Nominal resistance | 100 Ω at 0 °C |
| Nominal temperature coefficient | 0.003923 Ω/Ω/°C |
| Probe diameter | 3.2 mm |
| Probe lengths | 152, 229 or 305 mm |
| Sheath material | Stainless steel 316 |
| Connecting cable | Approx. 1.83 m |
| Cable insulation | PTFE |
| Cable conductor size | 22 AWG |
| Transition junction temperature | −50 °C to +200 °C |
| Hysteresis | <0.01 °C at 0 °C under specified conditions |
| Response time constant | ≤4 seconds under specified conditions |
| Calibration | Accredited manufacturer calibration included |
| Calibration coefficients | ITS-90 |
| Resistance-temperature table | 1 °C increments |
| Electrical termination | Various options |
| Compatible readouts | 1523, 1524, 1502A, 1529, 1560 |
| Typical applications | Reference thermometry and temperature calibration |
Calibration Service by europascal
Regular calibration is essential for maintaining reliable and traceable temperature measurements.
europascal provides professional calibration services for temperature measuring instruments and reference thermometers.
When the Fluke Calibration 5618B is used as a reference thermometer, the calibration uncertainty of the probe should be considered together with the uncertainty of the connected thermometer readout.
Additional uncertainty contributions may arise from temperature source stability, spatial temperature uniformity, immersion effects, repeatability and long-term drift.
For professional calibration services and metrological traceability, visit the europascal Calibration Service.
Why Choose the Fluke Calibration 5618B?
The Fluke Calibration 5618B combines precision temperature measurement with a compact industrial probe design.
Its temperature range from −200 °C to +500 °C covers demanding low-temperature and high-temperature calibration applications.
The slim 3.2 mm stainless steel sheath provides fast thermal response and helps reduce immersion errors.
Three available probe lengths allow the sensor to be selected according to the required installation conditions.
Individual ITS-90 calibration coefficients and an accredited manufacturer calibration support traceable reference measurements.
Compatibility with precision Fluke Calibration thermometer readouts makes the probe suitable for professional laboratory applications.
The Fluke Calibration 5618B is also particularly useful for verifying suitable infrared blackbody calibration sources.
For calibration laboratories, research facilities and industrial users requiring a precise and compact reference temperature probe, the Fluke Calibration 5618B provides an excellent combination of accuracy, flexibility and measurement stability.
europascal supports customers with professional temperature calibration equipment, technical advice and calibration services.
Typical Applications for the Fluke Calibration 5618B
Typical applications include:
- Reference temperature measurements
- Secondary reference thermometry
- RTD comparison calibration
- Calibration bath monitoring
- Dry block calibration
- Infrared calibrator verification
- Temperature stability measurements
- Low-temperature calibration
- Industrial temperature calibration
- Research and development
- Quality assurance
- Calibration laboratories
- Temperature metrology
The combination of a wide temperature range, small probe diameter, accredited calibration and excellent measurement performance makes the Fluke Calibration 5618B a professional solution for demanding temperature measurement applications.
Find more Fluke Calibration products here.
Manufacturer information for the Fluke Calibration 5618B can be found on the official Fluke Calibration website.
