Specification Sheet

2
K Series BASO Thermocouples Product Bulletin
D
escription
A thermocouple is constructed of two dissimilar metals;
one is a solid element, and that is surrounded by a
second, tubular-shaped piece. These metal elements
touch only at a single welded endpoint. This endpoint,
commonly known as the “hot” junction, is the tip of the
thermocouple heated by the pilot flame.
The outer element is brazed to a brass connector
sleeve attached to a copper tube, or is welded directly
to a copper tube. Inside the copper tube is an insulated
copper wire that is welded to the inner element of the
thermocouple. This welded joint, together with the
brazed joint between the copper tube or brass
connector and the outer thermocouple element, forms
the “cold” junction of the thermocouple. See Figures 2
and 3.
When there is a large temperature differential between
the hot and cold junctions, an electrical current is
generated. In its operating range, the electrical energy
created is directly proportional to the temperature
differential between the hot and cold junctions. The
electrical output of a thermocouple is small (measured
in millivolts) and the response time is slow (normally
30 to 45 seconds).
Care must be taken when applying a thermocouple to
an appliance. Only a large temperature differential
between the hot and cold junctions will create a useful
millivolt output. The thermocouple should be positioned
with 12.7 mm (0.5 in.) of its tip in the pilot flame. The
cold junction should not be subjected to any large
amounts of ambient heat. The lead should be routed
away from the heat of the pilot and main burners.
Electrical resistance increases with lead length, and
will create a noticeable power drop.
J
unction Block Thermocouples
K16F and K16J junction block thermocouples have a
built-in junction block, which allows for the connection
of a high limit switch. This type of application places
the power unit of the pilot control in series with the limit
switch and thermocouple so that all gas to the
appliance will be shut off if pilot flame failure occurs or
the high limit switch opens.
The correct length of the wire for connecting the limit
switch to the junction block is determined by several
factors: the size of the wire, the wire temperature, the
thermocouple lead length, the power unit type, and the
distance between the limit switch and the junction
block. The junction block is 90 mm (3.546 in.) from the
terminal end of the thermocouple for the K16F model,
and 60 mm (2.343 in.) for the K16J model.
T
hermocouple Output
Table 1: Thermocouple Output
Thermocouple
Type
Open Circuit
mV Range
Maximum Tip
Temperature
K15D, K15F
20-28 mV 816
°
C (1500
°
F)
K16B, K16F, K16J,
K16C, K16R
25-35 mV 816
°
C (1500
°
F)
K19
25-35 mV 704
°
C (1300
°
F)