Technical Data

Product and Ordering Information

Limits of Error

ANSI Limits of Error

Thermo Sensors’ thermocouple and extension wires are known for their quality performance and reliability. Careful attention is given to the proper selection and matching of conductors to ensure conformance to standard limits of error as defined in ANSI C96.1*. Tables on this page show the limits of error for both thermocouple and extension grade wires. Unless otherwise specified, all wire will be furnished to standard limits of error. Many of the wires are available with special limits of error and must be specified when ordering.

Thermo Sensors provides a calibration service for customers who require known deviations from specified temperature points. Each coil or spool of wire so certified is marked and a “Certificate of Calibration” is furnished. Certification temperatures available are -320°F, -110°F, 32°F, and 2000°F and must be specified by the customer. All equipment used in the certification is traceable tot he National Bureau of Standards.

*The American National Standards Institute (ANSI) designations have replaced the previous Instrument Society of America (ISA) designations for thermocouple materials. ANSI Standard C96.1-1975, or latest version, is the applicable standard for wires listed in this catalog unless otherwise noted.

Limits of Error for Thermocouple Wire

Reference Junction at 32°F

Sub-Zero Limits of Error

Thermocouple materials are normally supplied to meet the limits of error specified in the table for temperatures above 0°C. These materials, however, may not fall within the sub-zero limits of error given in the following table. If materials are required to meet the sub-zero limits, the purchase order must so state. Special pricing for selection of materials will be required.

Little information is available to justify establishing special limits of error for sub-zero temperatures. Limited experience suggests the following limits for types E and T thermocouples.

These limits are given only as a guide. Due to the characteristics of the materials, sub-zero limits of error for Type J thermocouples and special sub-zero limits for Type K thermocouples are not listed.

Limits of Error for Extension Wire

Reference Junction at 32°F

Limits of Error for Thermocouple Compensating Extension Wire

Reference Junction at 32°F

*Due to the non-linearity of the types of R, S, and B temperature – EMF curves, the error introduced into a thermocouple system by the compensating wire will be variable when expressed in degrees. The limits of error given in the table above are based on the following measuring junction temperatures:

Noise Sheilding

Wire for Electromagnetic and Electrostatic Noise Shielding

Electromagnetic Noise is produced due to capacitive coupling of an electric field within the plant to the instrument circuit. The source of these electric fields may be power lines or other voltage sources mentioned below. The most effective means of isolating static noise is to have the instrument circuit enclosed within a 100% coverage shield such as an aluminum backed mylar tape. a drain wire in contact with the aluminum foil carries the interference to the ground.

Magnetic Noise is generated anytime a loop of instrument wires pass through a magnetic field. As the wires come in the stray magnetic field of an electric motor, generator, power line, relay or similar source, a current is produced in the instrument circuit to oppose the magnetic field. That current super-imposed on the sensor signal results in an erroneous and usually unstable signal input at the instrument.

Electrostatic and magnetic noise sources include but are not limited to the following conditions:

Circuits near:

• Power lines
• Medium sized (SHP) and larger motors
• Control relays
• Transformers
• electrolytic processes
• Induction heating equipment

To minimize the effects of electrostatic and magnetic noise, the use of Thermo Sensors’ type PPZS extension wire is suggested. It incorporates both twisting, 100% shielding with an Aluminum/Mylar tape and drain wire. These wires are listed in the appropriate extension wire table.

ANSI Designations

ANSI Letter Designations

The tables listed below are provided to the user for a ready reference of ANSI designations as compared to the generic and trade names for the most common thermocouple materials. The letter “P” in the designation indicates the positive (+) leg of the calibration while the letter “N” designates the negative (-). Color coding and other means of conductor identification are also provided.

Thermocouple Grade Wire

Extension Grade Wire

*Trade names: Chromel, Alumel, Constantan – Hoekins Mfg. Co.

**Color Coding: Capton insulations will have a color fiber tracer under the Kapton singles. Overall insulations of Katpon and FEP are not color coded.

Some high temperature fibrous insultions are not color coded; others will have a colored tracer. The color pigment burns off at 300°F.

***Not ANSI Designations

Stranded Wire

Thermocouple and extension wires are usually solid conductors. When greater flexibility is needed, stranded wire is used. Both constructions are listed in the wire tables. The stranding combination used is given in the wire size column of the tables.