OVEN TRACKER XL2 Thermocouple Probes 35
Thermocouple Probes
Thermocouple probes utilize the Seebeck effect, discovered in the nineteenth
century, by which an e.m.f. is produced in any electrically conducting material
that is not at uniform temperature. The actual voltage measured is proportional
to the temperature difference between the thermocouple’s ‘hot’ and ‘cold’
junctions (the hot junction being the measurement junction, and the cold
junction being the junction of thermocouple and measurement instrumentation).
The practical implementation of thermocouples requires sophisticated
electronics to eliminate potential measurement errors which include poor
linearity over the measurement range, and inaccuracy due to temperature
variations at the cold junction. To accommodate these the electronics in the
measuring system must simulate a temperature of 0°C/32°F at the cold
junction, as well as compensating for any non-linearity over the range of
thermocouple operation.
Over the years, ‘standard’ thermocouples have been developed using materials
chosen for sensitivity, linearity (consistency of sensitivity over the useful
temperature range), price and availability. Current standards include types K,
N, R, S and T, each type being identified by its connector color.
Thermocouple Specifications
The standard thermocouple probe for oven operation is type K, which has a
hot junction combining nickel-chromium alloy and nickel-aluminum alloy.
International specifications for type K define a sensitivity and linearity over the
range 0–1,250°C/32–2,282°F, though operating range is limited in practice by
the cable insulation (see below).
Oven Tracker thermocouples supplied by Datapaq are exceptionally durable,
quad-wrapped, 10-strand 36 AWG (0.125 mm/0.005 inch).
Probe
Type
Temperature
Range
Cable Insulation Accuracy of Probes Supplied
by Datapaq
K -150°C to 1,370°C/
-238°F to 2,498°F
PTFE, ceramic,
mineral insulation,
glass fiber
±1.1°C/2.0°F (or ±0.4% if greater)
at 0–1,250°C/32–2,282°F
Type K thermocouples supplied by Datapaq formerly had yellow connectors and
red cables but are now supplied with green connectors and cables, following
the IEC584 color standard.
To Next Page
Loading...