THERMOCOUPLE INSTALLATION AND MAINTENANCE INSTRUCTIONS
Thermocouples are installed by means of spring-loaded, compression, welded or bayonet
fittings.
SPRING LOADED INSTALLATION
Follow these instructions for installation of a thermocouple with a spring-loaded fitting:
1. Insert the thermocouple into the process hole or opening.
2. Tighten the thermocouple into place by turning the thermocouple into the threaded
connection
Caution should be taken to disconnect the wires from the terminal block to prevent
twisting or shorting.
INSTALLATION:
- Vertical installation is preferred in very high temperatures to avoid protection tube or
element sagging.
- Install thermocouples away from AC power lines to prevent electrical noise.
- Do not run thermocouple wires in the same conduit with electrical wires.
- Do not run a single thermocouple to two different instruments. This will result in
instrument imbalance.
- A dual thermocouple should be used instead.
ELECTRICAL:
- Connect the positive thermocouple extension wire to the positive thermocouple wire
and the negative
- extension wire to the negative thermocouple wire. Wires are color coded for
identification as follow, notice that the negative leg is always red.
TYPE J - The positive element is magnetic. It has a lower resistance in ohms per foot than
the negative element in the same wire gauge.
TYPE K - The negative element is slightly magnetic. It has a lower resistance in ohms per
foot than the positive element in the same wire gauge.
TYPE E - The negative element has a lower resistance in ohms per foot than the positive
element for the same wire gauge.
TYPE T - The positive element is copper in appearance. It has a lower resistance per foot
in ohms than the negative element of the same wire gauge.
TYPE R or S - The negative element is softer. The positive element has a lower resistance
in ohms per foot than the negative element of the same wire gauge.
TYPE N - The positive element has a higher resistance in ohms per foot than the negative
element of the same wire gauge.
OPERATION:
- The temperature of the connection head should be kept at ambient temperature if
possible to avoid errors due to temperature gradient
- The maximum recommended temperature at the terminal block is 400°F.
MAINTENANCE:
- Thermocouples will deteriorate due to contamination from their environments. The
quality and frequency of calibration checks must be determined for each individual
application by noting the drift rate of each thermocouple at individual installations.
Calibration is usually made by comparison to a primary standard.
- The thermocouple may be removed from its installation and checked in a tube furnace
against the primary standard.
- Return thermocouples that were removed for tests to the same location and
immersion depth for reliable and repeatable readings.
- Do not use a thermocouple to measure a very low temperature if it has been used to
measure very high temperatures previously.
- Make sure the protection tubes and thermowells are in good condition when
protecting thermocouples with them.
STORAGE:
Store in a clean, dry place.
TYPE J - The positive element is magnetic. It has a lower resistance in ohms per foot than the
negative element in the same wire gauge.
TYPE K - The negative element is slightly magnetic. It has a lower resistance in ohms per foot
than the positive element in the same wire gauge.
TYPE E - The negative element has a lower resistance in ohms per foot than the positive element
for the same wire gauge.
TYPE T - The positive element is copper in appearance. It has a lower resistance per foot in
ohms than the negative element of the same wire gauge.
TYPE R or S - The negative element is softer. The positive element has a lower resistance in
ohms per foot than the negative element of the same wire gauge.
TYPE N - The positive element has a higher resistance in ohms per foot than the negative
element of the same wire gauge.