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Temperature Sensor Information
Temperature Sensor Questions
- For thermocouple cable and connectors, why are there two colours available for the same calibration?
- What is a Pt100?
- Should I choose a Type K or Type N thermocouple?
- I have an existing temperature probe, can Labfacility make a replacement?
- I have special sensor requirements, can Labfacility help?
- Are there other types of temperature sensor apart from thermocouple and PRT Types?
- Can I still purchase the old BS/ASTM colour code and why has everything gone over to IEC?
- Can Labfacility supply any installation fittings?
- How do I accurately measure a surface temperature?
- As most instrumentation only takes 2 or 3 wire Pt100s, if I took the correction made on the 3 wire system and incorporated that on to the single leg could I achieve a 4 wire system?
- If I added two identical cable lengths to a simplex sensor for two instrumentation units will I get the same reading as using a duplex sensor?
- Does Labfacility offer any publications to help technicians and students understand the choice and use of thermocouples and PRTs.
- Can I purchase a complete temperature measurement system from Labfacility?
- For thermocouple cable and connectors, why are there two colours available for the same calibration?
- Can you provide me with a sensor within 48 hours?
- Does it matter what type of steel I specify for the thermocouple sheath?
- There are several different types of extension cable construction; is the choice important?
- How do I choose between a thermocouple and a PRT?
- How long will my sensor last in the process?
- I use many thermocouples in testing and experiments, can I make my own thermocouple junctions?
- If I have a thermowell in my process; how much distance do I allow for my Temperature sensor to suit?
- Is a sensor with a calibration certificate more accurate than an uncalibrated one?
- My PRT is 1kOhm @ 0°C (Pt1000), not 100 Ohm (Pt100), can Labfacility supply an equivalent?
- My thermocouple is sited a long way from my controller, is this a problem?
- What accuracy loss will I get using a transmitter in line?
- What accuracy will I get at a certain temperature using a Pt100 detector; if a better grade detector is used what effect will this have to the accuracy?
- What do the thermocouple terms "cold junction compensation" and "linearisation" mean?
- What environments are 303,304,310,316,321, Inconel 600 and Nicrobell Suited to?
- What is the difference between a fabricated thermopocket and solid drilled Thermowell?
- What is the difference between a flat film and wire wound element?
- What is the minimum immersion depth for a PRT probe?
- What is the difference between a RTD and PRT sensor?
- What is the difference between Mineral Insulated (MI) and a fabricated sheath?
- What is the longest thermocouple I can have without losing accuracy?
- What is the practical difference between wire-wound and film RTDs?
- What type of Compression Fittings are available?
- What typical pressure are thermowells / thermopockets rated to and what is the Thermal response time of the thermowell?
- Which thermocouple type do I need for my application?
- Why are so many different types of thermocouple used?
- Why offer 2,3 or 4 wire PRTs
- Why should I use actual thermocouple connectors instead of ordinary electrical connectors?
- What sensor will I need to work in molten metal or a corrosive atmosphere?
- Why should I use an insulated hot junction sensor with instrumentation?
- Why use a Bayonet Fitting to install a probe..?
- Why use a Compression Fitting to fit a probe into a process?
- Why use a thermowell?
- Do I need a power supply when using a transmitter, and what length of extension lead can I run with a transmitter fitted?
- Does Labfacility offer a weatherproof, rugged sensor?
- How accurately can I measure temperature using a Labfacility sensor?
- I need to measure quickly changing temperature; what type of sensor should I use?
- What is a duplex sensor?
Temperature Sensor Answers
Q For thermocouple cable and connectors, why are there two colours available for the same calibration?
A Since December 1998, the International colour code to IEC 60584-3 should be observed.
Q What is a Pt100?
A An industry standard Platinum RTD with a value of 100 Ohms @0°C to IEC751; this is used in the vast majority of PRT assemblies in most countries.
Q Should I choose a Type K or Type N thermocouple?
A Generally, Type N is more stable and usually lasts longer than Type K; N is a better choice for high temperature work depending on the choice of sheath material.
Q I have an existing temperature probe, can Labfacility make a replacement?
A Yes, if it is a thermocouple or PRT. All we need is a sample, sketch or specification in order to quote.
Q I have special sensor requirements, can Labfacility help?
A Yes, we have 30 years of experience of sensor design and application.
Q Are there other types of temperature sensor apart from thermocouple and PRT Types?
A Several, but these two groups are the most common. Alternatives include thermistors, infra-red (non-contact), conventional thermometers (stem & dial types) and many others.
Q Can I still purchase the old BS/ASTM colour code and why has everything gone over to IEC?
A ANSWER
Labfacility can supply some products to the "old" obsolete BS colour but the current IEC standard is internationally recognised.
Q Can Labfacility supply any installation fittings?
A We manufacture installation fittings on site at the Bognor Regis branch and offer either from Stock or bespoke.
Q How do I accurately measure a surface temperature?
A Use an infra-red (non-contact) sensor instead of a thermocouple or PRT. - contact technical sales.
Information
Q As most instrumentation only takes 2 or 3 wire Pt100s, if I took the correction made on the 3 wire system and incorporated that on to the single leg could I achieve a 4 wire system?
A No. Cable length and ambient temperature variations come into play.
Q If I added two identical cable lengths to a simplex sensor for two instrumentation units will I get the same reading as using a duplex sensor?
A Yes, provided the instrument inputs are truly potentiometric and no measuring current is drawn. Not recommended.
Q Does Labfacility offer any publications to help technicians and students understand the choice and use of thermocouples and PRTs.
A Yes, the Labfacility Temperature Handbook
Q Can I purchase a complete temperature measurement system from Labfacility?
A Yes, there is a wide choice depending on budget and application requirements.
Q For thermocouple cable and connectors, why are there two colours available for the same calibration?
A Since December 1998, the International colour code to IEC 60584-3 should be observed.
Q Can you provide me with a sensor within 48 hours?
A Yes. You can order from our stock range of sensors; if you need an alternative we can provide a custom-made alternative within 7/10 days.
Q Does it matter what type of steel I specify for the thermocouple sheath?
A Often no, sometimes yes. In some cases, reliability depends on the ideal choice of material - contact "technical sales".
Q There are several different types of extension cable construction; is the choice important?
A Yes; some are waterproof, some mechanically stronger, some suitable for high or low temperature.
Q How do I choose between a thermocouple and a PRT?
A Mainly on the basis of required accuracy, probe dimensions, speed of response and the process temperature - refer to the Labfacility Temperature Handbook for full guidance.
Q How long will my sensor last in the process?
A Not known but predictable in some cases; this will be a function of sensor type, construction, operating conditions and handling. Contact "technical sales".
Q I use many thermocouples in testing and experiments, can I make my own thermocouple junctions?
A Yes, Labfacility can supply a benchtop welder and fine thermocouple wires - it is easy and inexpensive to make unsheathed thermocouples.
Q If I have a thermowell in my process; how much distance do I allow for my Temperature sensor to suit?
A An extra 50mm for a compression gland if used or probe length to fully seat into the well if a thread below head.
Q Is a sensor with a calibration certificate more accurate than an uncalibrated one?
A No. However, the errors and uncertainties compared with a reference sensor are published and corrected values can be used to obtain better measurement accuracy.
Q My PRT is 1kOhm @ 0°C (Pt1000), not 100 Ohm (Pt100), can Labfacility supply an equivalent?
A Yes, and some other values as well.
Q My thermocouple is sited a long way from my controller, is this a problem?
A It could be; try to ensure a maximum sensor loop resistance of 100 Ohms for thermocouples and 4-wire PRTs. Exceeding 100 Ohms could result in a measurement error. Note By using a 4-20mA transmitter near the sensor, cable runs can be much longer and need only cheaper copper wire. The instrument must be suitable for a 4-20mA input though.
Q What accuracy loss will I get using a transmitter in line?
A This depends on the accuracy of the specified transmitter; there will always be some degradation.
Q What accuracy will I get at a certain temperature using a Pt100 detector; if a better grade detector is used what effect will this have to the accuracy?
A Refer to the Labfacility Temperature Handbook for Pt100 tolerance information.
Q What do the thermocouple terms "cold junction compensation" and "linearisation" mean?
A Refer to the Labfacility Temperature Handbook for a full explanation. With most types of measuring instrument, these functions are automatically applied and do not require user consideration.
Q What environments are 303,304,310,316,321, Inconel 600 and Nicrobell Suited to?
A Depends on a combination of temperature and media.
Q What is the difference between a fabricated thermopocket and solid drilled Thermowell?
A A fabricated thermopocket uses a welded construction to allow for relatively long immersion lengths; a thermowell is machined from solid material.
Q What is the difference between a flat film and wire wound element?
A Film uses platinum deposition on a substrate; wire wound uses a helically wound Pt wire in ceramic. Wire-wound type provides greater accuracy and stability but is vulnerable to shock; film type is resistant to shock and has quicker thermal response.
Q What is the minimum immersion depth for a PRT probe?
A Usually 150mm or more; increase the immersion until the reading is unchanged.
Q What is the difference between a RTD and PRT sensor?
A Nothing. RTD means resistance thermometer detector (the sensing element) and PRT means Platinum resistance thermometer (the whole assembly) i.e. a PRT uses a RTD!
Q What is the difference between Mineral Insulated (MI) and a fabricated sheath?
A An MI is flexible, a fabricated sheath is rigid.
Q What is the longest thermocouple I can have without losing accuracy?
A It could be; try to ensure a maximum sensor loop resistance of 100 Ohms for thermocouples and 4-wire PRTs. Exceeding 100 Ohms could result in a measurement error. Note By using a 4-20mA transmitter near the sensor, cable runs can be much longer and need only cheaper copper wire. The instrument must be suitable for a 4-20mA input though.
Q What is the practical difference between wire-wound and film RTDs?
A Wire-wound type provides greater accuracy and stability but is vulnerable to shock; film type is resistant to shock and has quicker thermal response.
Q What type of Compression Fittings are available?
A Stainless Steel and Brass alternatives.
Q What typical pressure are thermowells / thermopockets rated to and what is the Thermal response time of the thermowell?
A Typically tens of bar and tens of seconds more than the sensor. Refer to a full supplier specification however - values vary.
Q Which thermocouple type do I need for my application?
A This depends on several factors including the nature of the process, heated medium and temperature. Refer to the Labfacility Temperature Handbook.
Q Why are so many different types of thermocouple used?
A They have been developed over many years to suit different applications world-wide.
Q Why offer 2,3 or 4 wire PRTs
A Because all 3 are encountered. Two-wire should be avoided, three-wire is widely used and four-wire gives optimum accuracy. Your instrument will be configured for 2,3 or 4 wire.
Q Why should I use actual thermocouple connectors instead of ordinary electrical connectors?
A Labfacility thermocouple connectors use thermocouple alloys, polarized connections and colour coded bodies to guarantee perfect, error-free interconnections.
Q What sensor will I need to work in molten metal or a corrosive atmosphere?
A There is no simple answer but special grades of Stainless Steel, Inconel 600, Nicrobell and Ceramics offer alternatives - consult Technical Sales.
Q Why should I use an insulated hot junction sensor with instrumentation?
A To eliminate the possibility of earth loops resulting in measurement errors and to reduce the danger of voltage pick up from electrical heaters.
Q Why use a Compression Fitting to fit a probe into a process?
A Use a Tapered Thread to obtain high pressure integrity or a Parallel Thread for general purpose.
Q Why use a thermowell?
A To protect the sensor from the process medium and to facilitate its replacement if necessary.
Q Do I need a power supply when using a transmitter, and what length of extension lead can I run with a transmitter fitted?
A A 24Vdc, 20mA supply will be needed if this is not incorporated in the measuring instrument. Long runs of copper cable can be used.
Q Does Labfacility offer a weatherproof, rugged sensor?
A We manufacture a wide range of weatherproof, rugged sensors. For more details on our range contact our Sales Team who will be pleased to advise you on the best solution for your apllication.
Q How accurately can I measure temperature using a Labfacility sensor?
A To published, internationally specified tolerances as standard, typically ( 2.5°C for popular thermocouples, (0.5°C for PRT. Higher accuracy sensors can be supplied to order, e.g. (0.5°C for type T thermocouple, (0.2°C for PRT. All of these values are temperature dependent. A close tolerance, 4-wire PRT will give best absolute accuracy and stability.
Q I need to measure quickly changing temperature; what type of sensor should I use?
A A fast-response (low thermal mass) thermocouple.
Q What is a duplex sensor? 
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