"Vaiseshika" Thermocouple Probes, Industrial Thermocouple Assemblies and RTD Probes
Introduction
A thermocouple is a sensor for measuring temperature. It consists of two dissimilar metals, joint together at one end, which produce a small unique voltage at a given temperature. This voltage is measured and interpreted by thermocouple thermometer.
Vaiseshika manufactures thermocouple available in different combinations of metals. The available thermocouples, J, K, T, R, S, B, E etc. Each type of thermocouple has a different temperature range and environment, although the maximum temperature varies with the diameter of the wire used in thermocouple.
Because thermocouples measure in wide temperature ranges and can be relatively rugged, they are very often used in industry. The following criteria are used in selecting a thermocouple :-
Temperature Range.
Chemical resistance of the thermocouple or sheath material.
Abrasion and vibration resistance.
Installation requirements like length, diameter and holding assembly.
Sheathed thermocouple probes are available with one of three junction types : grounded, ungrounded or exposed.
Description
'Vaiseshika" Thermocouples cover a wide range of temperature measurement in a number of solids, liquids and gases in a variety of applications in the industries like heat treatment, cement, glass and ceramics, chemical, iron and steel, noon-ferrous metals, power station etc.
Complete thermocouple assemblies, thermowells as well as spare parts are normally offered with quick deliveries. Special designs of thermocouple assemblies are also offered on request.
Thermowells:
Vaiseshika offers wide range of Industrial and Research Thermowells and Thermocouple assemblies. It includes a wide selection of components parts, partial assemblies and complete assemblies ready for installation.
In general the thermowell material to be chosen for an installation is governed mainly by the corrosion conditions the well will face. The high polish given to all stainless and monel wells provides maximum corrosion resistance.
Occasionally, the primary consideration is one of strength rather than corrosion resistance. For example a stainless steel well may be required for high pressure water service instead of brass well which would be satisfactory from a corrosion stand point.
The distance from the tip of the well to the underside of the thread or other connection means is the insertion length. For best accuracy, this length should be great enough to permit the entire temperature - sensitive part of the element to project into the medium being measured. A properly installed element will project into a liquid a distant equal to its sensitive length + atleast one inch. In air or gas, the element should be immerged its sensitive length + atleast three inches.
Vaiseshika is always glad to quote based on your special needs.
Protecting Sheaths
The thermocouples mentioned above need protection against mechanical injury and chemical attack. Metallic or ceramic protecting sheaths are provided as a cover for the thermocouple element.
Metallic Protecting Sheaths:
These are suitable for uses upto the temperature approximately 1200°C maximum, depending on the particular application. Our standard diameter of these sheaths are 22mm outer diameter (OD) and 3mm wall thickness. Other diameters from 4mm to 52mm outer diameter in various wall thickness are available on request.
Ceramic Protecting Sheaths:
These are suitable beyond 1200°C. Ceramic sheaths are sometimes used as additional covering along with either metallic or ceramic outer sheath for special applications.
Sheath Materials
Sheath
Melting Point ºC
Usable Temp. ºC
Characteristics
SS-304
1400
900
High Resistance to heat and corrosion.
SS-316
1400
900
Excellent resistance to heat, acids and alkalies.
SS-310
1410
1150
Good oxidation resistance and sulphur atmospheres at low temperature.
SS-321
1400
900
Excellent resistance to corrosion.
HRS-446
1400
1150
Good oxidation resistance at elevated temperature & sulphur atmosphere.
Inconel 600
1410
1150
Excellent oxidation resistance (do not use in sulphur atmosphere.
Ceramic 610
1600
Excellent thermal, mechanical, electrical and corrosion resistant.
Thermocouple Calibration
Type
Thermocouple
Calibration
Equipment calibration
Temperature Range ºC
K
Chromel-Alumel
IS : 2054
IPTS-1968
DIN 43710
BS 4937 iv
0-1200
T
Copper-Constanton
IS : 2056
IPTS-1968
DIN 43710
BS 4937 v
0-400
J
Iron-Constantan
IS : 2057
IPTS-1968
ANSI/MC96
BS 4937iii
0-900
R
Pt 13% Rh-Pt
IS : 2055
IPTS-1968
DIN 43710
BS 4937 ii
0-1600
S
Pt 10% Rh-Pt
IS : 2055
IPTS-1968
DIN 43710
BS 4937 i
0-1600
B
Pt 30% Rh-Pt 6% Rh
IS : 6270
IPTS-1968
DIN IEC B8
BS 4937 vii
0-1800
RTD Probes, Elements and Assemblies
Description:
RTD means Resistance Temperature Detector which operates on the principle of the change in electrical resistance in wire as a function of temperature. RTDs consist of an element and probe. An element is the actual temperature sensing unit whereas probe is an assembly composed of an element, a sheath, a lead wire and a termination or connection.
Probes may be terminated in a connector head, quick disconnect, terminal block or extension wire.
Lead styles are offered in generally four configuration namely :
Two wire Element Input : (Style 1)
This construction is suitable where the resistance of the run of the lead wire may be considered as an additive constant in the circuit and particularly where the changes in the lead resistance due to ambient temperature changes can be ignored.
Style 1 is a grounded junction thermocouple with the Inconel overbraid welded to form a smooth rounded tip for all general purpose applications.
.
Three Wire Element Input : (Style 2)
In this configuration compensation is achieved for lead resistance and temperature change in lead resistance. This is the most commonly used configuration
Style 2 is a general purpose, bead welded, exposed junction thermocouple.
Four Wire Element Input : ( Style 3)
Here two connections to each end of the sensor are given. This construction is used for measurements of the highest precision.
Style 3 is an exposed, bead welded junction thermocouple with an Inconel collar to clamp the probe to a surface, or to secure it into a hole or any fabrication.
Four Wire Element Input (Lead Resistance Loop) : ( Style 4)
Here a separate pair of wires is provided as a loop to provide compensation for lead resistance and ambient temperature changes in lead resistance.
The standard RTD probe is made with a 100 ohm platinum European curve element (alfa = 0.00385). Standard RTD probe assemblies are rated for use in temperatures upto 600 Deg. C. The maximum temperature rating is available on special order is 750 Deg. C.
Where accuracy over a wide temperature range is a crucial factor in industry, platinum RTDs are unequalled in performance. Stability over long periods of continued use makes them unmatched for reliability.
Quick Disconnect Connectors for RTDs
And Thermocouples
These connectors are used for easy disconnection of thermocouples. These are made of solid pin construction for maximum durability and service. Large terminal screw for easy wire installation and colour coding to match thermocouple calibration are some of the other features of these connectors.
