Page 698 - Plastic Process Equipment, Inc

PRINCIPLES OF THERMOCOUPLES & RTD'S

— RTD's —
GENERAL INFORMATION
Resistance Temperature Detectors (RTD's) are made by winding a platinum wire or plating a film on a ceramic or glass
core and hermetically sealing this element. They function by the variance in resistance created by the change in temperature
at the element. A small current is passed through the element and the voltage, which is proportional to the resistance, is
measured and converted to units of temperature. Advantages of using a RTD include better accuracy, stability, and repeatability.
CONSTRUCTION
Because RTD's measure very small resistances, the resistance of the leadwire itself may affect the accuracy of the reading.
To compensate for this, 3-wire or 4-wire construction may be used (if your instrument is designed to accept this construction).
The extra wires provide a means for the instrument to remove the leadwires from the measuring circuit, thus cancelling out
their resistance from the reading. For runs of less than 10 feet, this factor is negligible.

2-WIRE 3-WIRE 4-WIRE

— GUIDE TO THERMOCOUPLE CONDUCTORS —

ISA Conductor Characteristics Temperature Limits of Error Application Notes
Code Positive Color Negative Color Range (°F) Standard Special
Iron Constantan 0 to 530 ± 4°F ± 2°F
J White Red Reducing atmosphere recommend.
(Magnetic) (Non-Magnetic) 530 to 1400 ± 3/4% ± 3/8%
Chromel Alumel 0 to 530 ± 4°F ± 2°F
K Yellow Red Oxidizing atmosphere recommended.
(Non-Magnetic) (Magnetic) 530 to 2300 ± 3/4% ± 3/8%
Constantan -75 to 200 ± 1-1/2°F ± 3/4°F Can be used in oxidizing or reducing
T Copper Blue Red
(Silver Metal) 200 to 700 ± 3/4% ± 3/8% atmospheres: corrosion resistant.
0 to 600 ± 3°F - Oxidizing atmosphere recommended
E Chromel Purple Constantan Red
600 to 1600 ± 1/2% ± 3/8% Highest emf output.
INTERNATIONAL THERMOCOUPLE & EXTENSION WIRE COLOR CODES

U.S. U.S. International International Czech Netherlands Japan French
ANSI ANSI/ASTM ANSI/ASTM IEC 584-3 IEC 584-3 British Germany to to
Code E-230 E-230 TC Grade Intrinsically to to JIS NFE-18001
TC Grade Extension Safe BS 1843 DIN 43710 C 1610-1981

White White Black Black Yellow Red Red Yellow
J Brown Red Black Red Black White Blue White Black Blue Blue Blue Yellow Yellow Black Black

Yellow Yellow Green Green Brown Red Red Yellow
K Brown Red Yellow Red Green White Blue White Red Blue Green Green Blue White Yellow Purple

PLASTIC PROCESS EQUIPMENT, INC. www.ppe.com
e-mail: sales@ppe.com
E 8303 CORPORATE PARK DRIVE W 6385 MONTESSOURI STREET
A MACEDONIA, OHIO 44056-2300 E LAS VEGAS, NEVADA 89113-1186 Toll Free: USA, Canada & Mexico
S 216-367-7000 • FAX: 216-367-7022 S 702-433-6385 • FAX: 702-433-6388 800-362-0706
T TOLL FREE: 800-321-0562 T TOLL FREE: 800-258-8877 Order Fax: 800-223-8305
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