310201c Thermocouples Flashcards
What are the three most common types of thermocouples
- Type J
- Type K
- Type T
What is the color coding for the negative conductor in all thermocouples?
The color coding for negative conductors in a thermocouple is always RED
Name the two metals used to construct type K thermocouples
Chromel (+)
Alumel (-)
Name the two metals used to construct type J thermocouples
Iron (+)
Constantan (-)
Name the two metals used to construct type T thermocouples
Copper (+)
Constantan (-)
What is the overall jacket wire color for a type J thermocouple
Type J thermocouple = black
What is the overall jacket wire color for a type K thermocouple
Type K thermocouple = yellow
The ______ ______ describes the redistribution of electrons when one end of a conductor is heated
The seed back effect describes the redistribution of electrons when one end of a conductor is heated
Which thermocouple provides the most linear response to a change in temperature?
Type K Thermocouple
Define the law of intermediate metals
The introduction of a third medal into the circuit has no effect upon the output voltage generated if the junctions created by the third metal are the same temperature
Why is solving for temperatures using thermocouple tables more accurate than using Seebeek coefficient?
The non-linearity of the temperature voltage-relationship causes the Seebeek coefficient to change.
Thermocouple tables are adjusted for nonlinearity.
What are three ways of compensating for junction temperature changes?
- Constant temperature chambers
- Software compensation
- Hardware compensation
What is the purpose of reference junction compensation
To automatically compensate for changes in reference junction temperature
What is the major advantage of using software compensation for reference junction temperature correction?
Software compensation is the most versatile way to compensate for the reference junction because it allows for any type of thermocouple to connect to the same transmitter
What are the two differences between thermocouple grade wire and extension grade wire?
- Thermocouple wire is of a higher purity than extension grade wire
- Thermocouple wire has a higher temperature limit than extension grade wire
What is the upper temperature limit for a Type T Thermocouple?
400°C
What is the most widely used thermocouple
Type J
What are the four common methods for joining thermocouple wires?
- Electric Arc Weld
- TIG
- Solder
- Resistance Weld
What is the purpose of using an inert gas when using the TIG method of joining thermocouple wires
Inert gases suchas nitrogen or argon, protect the weld/metal from atmospheric contamination, it shields the metal and eliminates the need for flux
List three common connection types for thermocouples at the measurement end
- Twist end
- Butt end
- V Type
Does a grounded or ungrounded sheated thermocouple provide a quicker response time to a temperature change?
A grounded thermocouple
When would you choose a welded thermowell over a threaded design?
In high pressure applications over 9MPag/1300psig
