Labfacility temperature and process technology
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FREQUENTLY ASKED QUESTIONS
Remember, the sensor type must always suit the measuring instrument and employ the correct extension cable. Information given here is for general guidance only and is not definitive - it is not intended to be the basis for product installation or decision making. Labfacility Ltd can not be held responsible for any misinterpretation or incorrect assumptions based on these Questions and Answers.
CATEGORIES
Thermocouple Connectors
Temperature Sensors
Thermocouple Cables
Calibration
Instruments
TEMPERATURE SENSORS
What is a Pt100?
Should I choose a Type K or Type N thermocouple?
I have special sensor requirements, can Labfacility help?
Are there other types of temperature sensor apart from thermocouple and PRT Types?
How do I accurately measure a surface temperature?
Can Labfacility supply any installation fittings?
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?
Can I purchase a complete temperature measurement system from Labfacility?
Can I still purchase the old BS/ASTM colour code and why has everything gone over to IEC?
Can you provide me with a sensor within 48 hours?
Does it matter what type of steel I specify for the thermocouple sheath?
Does Labfacility offer any publications to help technicians and students understand the choice and use of thermocouples and PRTs.
For thermocouple cable and connectors, why are there two colours available for the same calibration?
How can I keep abreast of new developments, products and services from Labfacility?
How do I choose between a thermocouple and a PRT?
How long will my sensor last in the process?
I have an existing temperature probe, can Labfacility make a replacement?
I use many thermocouples in testing and experiments, can I make my own thermocouple junctions?
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?
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 @ 0oC (Pt1000), not 100 Ohm (Pt100), can Labfacility supply an equivalent?
My thermocouple is sited a long way from my controller, is this a problem?
There are several different types of extension cable construction; is the choice important?
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 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 minimum immersion depth for a PRT probe?
What is the practical difference between wire-wound and film RTDs?
What sensor will I need to work in molten metal or a corrosive atmosphere?
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?
Why should I use an insulated hot junction sensor with instrumentation?
Why specify a Swaged Tip?
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?
QUESTIONS & ANSWERS
What is a Pt100?

An industry standard Platinum RTD with a value of 100 Ohms @0oC to IEC751; this is used in the vast majority of PRT assemblies in most countries.
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Should I choose a Type K or Type N thermocouple?

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.

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I have special sensor requirements, can Labfacility help?

Yes, we have 30 years of experience of sensor design and application.
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Are there other types of temperature sensor apart from thermocouple and PRT Types?

Several, but these two groups are the most common. Alternatives include thermistors, infra-red (non-contact), conventional thermometers (stem & dial types) and many others.
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How do I accurately measure a surface temperature?

Use an infra-red (non-contact) sensor instead of a thermocouple or PRT. - contact technical sales.
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Can Labfacility supply any installation fittings?

We manufacture installation fittings on site at the Bognor Regis branch and offer either from Stock or bespoke.
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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?

No; cable length and ambient temperature variations come into play.

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Can I purchase a complete temperature measurement system from Labfacility?

Yes, there is a wide choice depending on budget and application requirements.

Labfacility E-mail Newsletter - click here for registration.
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Can I still purchase the old BS/ASTM colour code and why has everything gone over to IEC?

Labfacility can supply some products to the "old" obsolete BS colour but the current IEC standard is internationally recognised.

click here for the IEC colour codes

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Can you provide me with a sensor within 48 hours?

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.

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Does it matter what type of steel I specify for the thermocouple sheath?

Often no, sometimes yes. In some cases, reliability depends on the ideal choice of material - contact "technical sales".
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Does Labfacility offer any publications to help technicians and students understand the choice and use of thermocouples and PRTs.

Yes, the Labfacility Temperature Handbook - To receive your free copy click here


Labfacility E-mail Newsletter - click here for registration.


ALL Labfacility Brochures now available in a PDF downloadable format - click here
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For thermocouple cable and connectors, why are there two colours available for the same calibration?

Since December 1998, the International colour code to IEC 60584-3 should be observed.

Labfacility E-mail Newsletter - click here for registration.
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How can I keep abreast of new developments, products and services from Labfacility?

Labfacility E-mail Newsletter - click here for registration.

NOTE: Our PDF Feature button on the website is regularly being updated with new Labfacility Product Literature
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How do I choose between a thermocouple and a PRT?

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.
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How long will my sensor last in the process?

Not known but predictable in some cases; this will be a function of sensor type, construction, operating conditions and handling. Contact "technical sales".

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I have an existing temperature probe, can Labfacility make a replacement?

Yes, if it is a thermocouple or PRT. All we need is a sample, sketch or specification in order to quote.

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I use many thermocouples in testing and experiments, can I make my own thermocouple junctions?

Yes, Labfacility can supply a benchtop welder and fine thermocouple wires - it is easy and inexpensive to make unsheathed thermocouples.

For more information click here

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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?

Yes, provided the instrument inputs are truly potentiometric and no measuring current is drawn. Not recommended.

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If I have a thermowell in my process; how much distance do I allow for my Temperature sensor to suit?

An extra 50mm for a compression gland if used or probe length to fully seat into the well if a thread below head.

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Is a sensor with a calibration certificate more accurate than an uncalibrated one?

No. However, the errors and uncertainties compared with a reference sensor are published and corrected values can be used to obtain better measurement accuracy.

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My PRT is 1kOhm @ 0oC (Pt1000), not 100 Ohm (Pt100), can Labfacility supply an equivalent?

Yes, and some other values as well.

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Top
My thermocouple is sited a long way from my controller, is this a problem?

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.

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There are several different types of extension cable construction; is the choice important?

Yes; some are waterproof, some mechanically stronger, some suitable for high or low temperature -

Click here to contact our sales team

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**View PDF Literature on the new PDF Feature button on our Home Page **
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What accuracy loss will I get using a transmitter in line?

This depends on the accuracy of the specified transmitter; there will always be some degradation - consult Technical Sales.

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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?

Refer to the Labfacility Temperature Handbook for Pt100 tolerance information.

To apply for your free copy simply click here

Labfacility E-mail Newsletter - click here for registration.
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What do the thermocouple terms "cold junction compensation" and "linearisation" mean?

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.

Labfacility E-mail Newsletter - click here for registration.

Get your free copy now simply click here and follow the on screen instructions.
Top
What environments are 303,304,310,316,321, Inconel 600 and Nicrobell Suited to?

Depends on a combination of temperature and media. Consult technical sales.

Labfacility E-mail Newsletter - click here for registration.
Top
What is the difference between a fabricated thermopocket and solid drilled Thermowell?

A fabricated thermopocket uses a welded construction to allow for relatively long immersion lengths; a thermowell is machined from solid material.

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What is the difference between a flat film and wire wound element?

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.

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What is the difference between a RTD and PRT sensor?

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!
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What is the difference between Mineral Insulated (MI) and a fabricated sheath?

An MI is flexible, a fabricated sheath is rigid.

Labfacility E-mail Newsletter - click here for registration.
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What is the longest thermocouple I can have without losing accuracy?

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.
Top
What is the minimum immersion depth for a PRT probe?

Usually 150mm or more; increase the immersion until the reading is unchanged.

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Top
What is the practical difference between wire-wound and film RTDs?

Wire-wound type provides greater accuracy and stability but is vulnerable to shock; film type is resistant to shock and has quicker thermal response.

Labfacility E-mail Newsletter - click here for registration.
Top
What sensor will I need to work in molten metal or a corrosive atmosphere?

There is no simple answer but special grades of Stainless Steel, Inconel 600, Nicrobell and Ceramics offer alternatives - consult Technical Sales.
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What type of Compression Fittings are available?

Stainless Steel and Brass alternatives- please see our TURNED PARTS brochure for our product range.
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What typical pressure are thermowells / thermopockets rated to and what is the Thermal response time of the thermowell?

Typically tens of bar and tens of seconds more than the sensor. Refer to a full supplier specification however - values vary.

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Which thermocouple type do I need for my application?

This depends on several factors including the nature of the process, heated medium and temperature. Refer to the Labfacility Temperature Handbook.

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Why are so many different types of thermocouple used?

They have been developed over many years to suit different applications world-wide.

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Why offer 2,3 or 4 wire PRTs

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.