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Temperature Instrumentation Information
Temperature Instrumentation Questions
- How accurately can I measure temperature using a Labfacility sensor?
- Can I purchase a complete temperature measurement system from Labfacility?
- My thermocouple is sited a long way from my controller, is this a problem?
- I use many thermocouples in testing and experiments, can I make my own thermocouple junctions?
- Does Labfacility offer any publications to help technicians and students understand the choice and use of thermocouples and PRTs?
- Why should I use actual thermocouple connectors instead of ordinary electrical connectors?
- Why offer 2,3 or 4 wire PRTs?
- For thermocouple cable and connectors, why are there two colours available for the same calibration?
- What do the thermocouple terms ‘cold junction compensation’ and ‘linearisation’ mean?
- Do I need a power supply when using a transmitter, and what length of extension lead can I run with a transmitter fitted?
- What accuracy loss will I get using a transmitter in line?
- 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?
- What is the maximum number of calibration points I can have programmed in to a Tempmaster-100?
- 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?
- Why should I use an insulated hot junction sensor with instrumentation?
- What is Automatic Cold Junction Compensation?
- Is there a more compact version of the usual in-head transmitter?
- Do all Labfacility in- head transmitters use DIN standard pitch for the fixing holes?
- Can I re-calibrate and / or re-scale the 300TXL Transmitter?
- Is the 300TXL Transmitter CE and RoHS Compliant?
- Can I re-fit a Temperature Transmitter without changing the Thermocouple or PRT Sensor?
- Do I need an enclosure (head) for the ILTX Transmitter?
- What is the advantage in using inline Transmitters as opposed to an in-head alternative?
- Is an in-line transmitter less accurate than an in-head alternative?
- Do I need special wiring for use with a Labfacility Transmitter?
- If the Labfacility in-line Transmitter uses plug-in conections is there a danger of reversing polarity?
- Can I cross-connect input and output re Labfacility ILTX Transmitter?
- Is the Labfacility ILTX Transmitter CE and RoHS Compliant?
- Can I re-calibrate and/or re-scale the Labfacility In Line Transmitter?
- Can I retro - fit a Temperature Transmitter?
Temperature Instrumentation Answers
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 Can I purchase a complete temperature measurement system from Labfacility?
A Yes, there is a wide choice depending on budget and application requirements.
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 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 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 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 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 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 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 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 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 - consult Technical Sales.
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 What is the maximum number of calibration points I can have programmed in to a Tempmaster-100.
A Ten
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 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 What is Automatic Cold Junction Compensation?
A This is a feature of most measuring instruments which allows for the fact that the thermocouple input termination is at a varying temperature other than stable at 0°C.
Q Is there a more compact version of the usual in-head transmitter?
A Yes, the Labfacility 300TXL ( low profile) is more compact for use in housings with a smaller depth. Overall height is only 23mm.
Q Do all Labfacility in- head transmitters use DIN standard pitch for the fixing holes?
A Yes
Q Can I re-calibrate and / or re-scale the 300TXL Transmitter?
A Yes, quickly and simply; there is a minimal interaction between the span and zero potentiometer adjustments.
Q Can I re-fit a Temperature Transmitter without changing the Thermocouple or PRT Sensor?
A Yes, using the Labfacility ILTX Transmitter - this simply connects to the existing sensor output wires.
Q Do I need an enclosure ( head) for the ILTX Transmitter?
A No, it connects in-line using miniature connectors and does not require any housing.
Q What is the advantage in using inline Transmitters as opposed to an in-head alternative?
A Convenience and cost saving. The process sensor does not need to be replaced and downtime is much reduced. An expensive head terminated probe assembly is therefore not required.
Q Is an in-line transmitter less accurate than an in-head alternative?
A No, performance will be identical to an equivalent alternative.
Q Do I need special wiring for use with a Labfacility Transmitter?
A No, but screened cable with copper conductors is advised.
Q If the Labfacility in-line Transmitter uses plug-in conections is there a danger of reversing polarity?
A No, as the connections are polarized to prevent this.
Q Can I cross-connect input and output re Labfacility ILTX Transmitter?
A Yes, but colour coded connections are used to prevent accidental cross connection.
Q Can I re-calibrate and/or re-scale the Labfacility In Line Transmitter?
A Yes, quickly and simply; there is a minimal interaction betweeen the span zero potentiometer adjustments.
Q Can I retro - fit a Temperature Transmitter?
A Yes, provided that the wiring and host instrument are suitable.
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