User manual

USB TC-08 User's Guide 9
Copyright © 2005-2012 Pico Technology Limited. All rights reserved. usbtc08.en
4 Glossary
Cold junction compensation (CJC). A method of compensating for ambient
temperature variations in thermocouple circuits.
Common mode range. The voltage range, relative to the ground of the data logger,
within which both inputs of a differential measurement must lie in order to achieve an
accurate measurement.
DLL. Dynamic Link Library. Files with this file extension contain a collection of
Windows functions designed to perform a specific class of operations.
Input impedance. The resistance measured between the input terminals of a
circuit.
NFR. Noise-Free Resolution. The effective number of bits of resolution that can be
considered noise-free.
Overvoltage protection. The maximum input voltage that can be applied without
damaging the unit.
Resolution. A value in bits, related to the number of increments of an analog input
signal that can be detected by a digital measurement system. A high-resolution
measurement system detects smaller signal increments than a low-resolution
measurement system.
Thermocouple. A device consisting of two dissimilar metals joined together. The
thermoelectric voltage developed between the two junctions is proportional to the
temperature difference between the junctions.
Type B thermocouple. Type B thermocouples are made from platinum and rhodium
and are suitable for high temperature measurements of up to 1820°C. Unusually, due
to the shape of their temperature / voltage curve, type B thermocouples give the
same output at 0°C as at 42°C.
Type E thermocouple. Type E thermocouples are made from chromel and
constantan. They have a high output (68 uV/°C), making them well suited to low-
temperature (cryogenic) use. They are non-magnetic.
Type J thermocouple. Type J thermocouples are made from iron and constantan.
They measure temperatures in the range -210 to +1200°C. The main application is
with old equipment that can not accept the more modern thermocouple. J types
should not be used above 760°C, as an abrupt magnetic transformation will cause
permanent decalibration.
Type K thermocouple. Type K thermocouples are low-cost, general-purpose
thermocouples, made from chromel and alumel, operating in the -270°C to +1370°C
temperature range. Sensitivity is approx 41 uV/°C.
Type N thermocouple. Type N thermocouples are made from nicrosil and nisil. The
high stability and resistance to high-temperature oxidation of these thermocouples
make them suitable for measuring high temperatures. They are less expensive than
platinum types B,R, and S and were designed to be an improved type K.
Type R thermocouple. Type R thermocouples are made from platinum and rhodium,
and are suitable for high-temperature measurements of up to 1760°C. Low sensitivity
(10 uV/°C) and high cost make them unsuitable for general purpose use.