7. RESISTANCE TEMPERATURE DETECTORS
AND TABLE
64
There are many RTD types available on today’s market. Each
has its own particular advantages and disadvantages. In many
cases, RTD’s and their accessories are designed for a specifc
temperature measurement problem. In other cases, RTD’s are
manufactured with a wide variety of possible applications. It is
not the intention to compare one RTD type with another, or to
compare the RTD of one manufacturer with another. RTD’s must
be selected to meet the needs of a particular installation.
Two examples as a guide in the selection process:
• Tube type construction
• Mineral insulated type
Tube type construction
The most basic RTD construction is the tube type construction.
The wires can be made of several materials (depending on the
temperature range) such as copper, silver or nickel clad copper
wire.
The insulation material of the wires can be PVC, Silicon or PTFE
insulators for temperature up to 250 °C. Above this temperature
the isolation material will be ceramic. The total construction is
not bendable and is normally not used in applications with a lot
of vibrations.
RTD BODY CONSTRUCTION (PT100)
Resistance Thermometer
Connection Leads
Insulator
Sheath
Connection
to leads
A basic construction for RTD’s