Protection Tube Type Resistance Thermometer Sensors

Protection tube type resistance thermometer sensors are conventional resistance thermometer sensors, whose structure aims at protecting a resistance element from the atmosphere of the measuring target. Currently, sheathed resistance thermometer sensors are used in most products; however, the protection tube type is used in some products since manufacturing the sheathed type is more difficult and there is a limitation on costs. For special purposes of use, plastic insulated/coated resistance thermometer sensors are used.

Protection Tube Type Resistance Thermometer Sensors image

Principle of Platinum Resistance Thermometer Sensors

Generally, the electrical resistance of metal changes with the temperature. Especially, platinum is characterized by linear relationship of the change and larger temperature coefficient compared to other metals; therefore, platinum is suitable for temperature measurement. Platinum is likely to be obtained with high purity because of its excellent chemical and physical characteristics; as a result, it can be stably used as a resistance element for a long period of time. The characteristics have been standardized by JIS and other overseas standards, and temperature measurement with high accuracy is available.


The resistance thermometer sensor consists of an resistance element, internal conducting wire, insulation tube, Protection Tube, terminal box, necessary mounting bracket, etc.

  • 1.Resistance Elements

    The thermometry resistance element is made of our high accuracy ceramic element (CERACOIL), and it is fixed inside the protection tube with a stainless fin and good heat conduction.

  • 2.Internal Conducting Wires

    The internal conducting wire connects the resistance element to the terminal. The 3-wire type of the conducting wire is the standard; however, we also manufacture 2-wire type and 4-wire type conducting wires. We use nickel for conducting wires.

  • 3.Insulator

    Insulators are used for insulation between internal conducting wires and short-circuit prevention. We use glass tubes for low and medium temperature measurement and porcelain insulators for high temperature measurement.

  • 4.Protection Tubes

    Protection tubes protect resistance elements and internal conducting wires from its ambient environment, and mounting brackets and terminal box, etc. are attached to the tubes. Since each temperature measuring place has a different use temperature, atmosphere, purpose, etc., materials and forms suitable for the conditions must be selected for protection tubes.

  • 5.Terminal Boxes and Terminal Plates

    The terminal box connects the resistance thermometer sensor to the external conducting wire. We have drip-proof type EL terminal boxs (made of aluminum die-casting) and other types of materials and forms suitable for use purposes.

  • 6.Mounting Brackets

    A mounting bracket is attached to a Protection Tube to install the resistance thermometer sensor onto a measuring place.

We have other products of a structure where, at an end of a plastic insulated electric wire, a resistance element is molded with resin of the same material and embedded to be united with the wire. The highest usable temperature of the temperature sensors made of polyethylene is approx. 80℃; however, the temperature sensors made of FEP (Perfluoro ethylene propylene copolymer) can be used at approx. -200 to 180℃. The sensors can be used for sea water thermometers used in a drainage canal, etc. and thermometers used in soil.

Types of Resistance Thermometer Sensors

Nominal resistance value at 0℃ Class Measured current R100/R0 (Resistance ratio)
Pt100Ω(JPt100Ω) AA 2mA,1mA,0.5mA 1.3851(1.3916)


  • R100 is the resistance value of the resistance element at 100℃.
  • R0 is the resistance value of the resistance element at 0℃.
  • JPt 100 has been abolished.

List of Tolerance for Temperature and Standards Applied by Each Country

Basic standard
Nominal resistance
Class Tolerance(℃) JIS C1604/IEC 60751 ASTM E1137
Winding element Thin film element
Temperature range(℃)
Pt100Ω at 0℃
AA ±〔0.1+0.0017|t|〕 -196 to 450 0 to 150
A ±〔0.15+0.002|t|〕 -196 to 450 -30 to 300
±〔0.13+0.0017|t|〕 -200 to 650
B ±〔0.3+0.005|t|〕 -196 to 600 -50 to 500
±〔0.25+0.0042|t|〕 -200 to 650
C ±〔0.6+0.01|t|〕 -196 to 600 -50 to 600


  • The tolerance is the maximum limit on the allowable errors of the resistance value indicated by the resistance element converted with the standard resistance value table subtracting the measured temperature |t|.
  • |t| is the measured temperature which is indicated with the temperature (℃) unrelated to + and - signs.
  • The standard year is applied to the latest version.

Connection Method and Color Indication of Resistance Thermometer Sensors

JIS type/IEC type

JIS type/IEC type image

ASTM type

ASTM type image

※ASTM standard has no double element requirements. For double elements, IEC standard is applied.

  • 2-conducting wire type:

    Since the conducting wire resistance value is added to the resistance value, the conducting wire resistance must be decreased or must be known in advance. This type is rarely used except for the case of a relatively high resistance.

  • 3-conducting wire type:

    Since the variation of the resistance of three conducting wires affects the accuracy, attention must be paid in the case of long distance transmission. Generally, this type is used most frequently.

  • 4-conducting wire type:

    Since the resistance of conducting wires does not affect the accuracy, this type is used for measurement with high accuracy. Generally, the constant current is sent and the resistance value is measured with the potential difference in order to measure resistance value.

Usable Temperature Range of Resistance Thermometer Sensors

Symbol Category Use temperature range(℃)
L For low temperature -196 to +100
N For normal temperature -30 to +200
M For medium temperature 0 to 350
H For high temperature 0 to 600 ※1

※1For JPt100, the temperature shall be up to 500℃.

Standard Dimensions of Metal Protection Tubes

JIS code is in ( ).
Material code Dimension(φ/mm) Max. length
Common use temperature
Outer diameter Inner diameter
A 10 7 2000 900 Excellent at heat/acid/alkali resistance. Weak against sulfur and reducing gas.
12 9
15 11 3950
C 10 7 2000 900 Heat/acid/alkali resistance is the same as the resistance of 304SS; however, corrosion resistance is excellent at high temperatures.
12 9
15 11 3950
316L SS
CL 12 9 2000 900 The amount of C is less than that of 316SS, and the material has grain-boundary corrosion resistance.
15 11 3950
TITANIUM T 15 11 3950 250 Corrosion resistance is extremely excellent at low temperatures; however, the material becomes fragile with oxidation at high temperatures.

※1The common use temperature limits were described referring to JIS and manufacturer’s catalog;
therefore, they are not guaranteed values.

Basic Model

RBN: Resistance Thermometer Sensor with Terminal Box

The most basic model used in combination with a protection tube.

RBN: Resistance Thermometer Sensor with Terminal Box image

RBW: Resistance Thermometer Sensor with Outdoor Type Metal Protection Tube

This type has a drip-proof type terminal box attached to a metal protection tube, suitable for use in an outdoor general environment.

RBW: Resistance Thermometer Sensor with Outdoor Type Metal Protection Tube image

RBG: Resistance Thermometer Sensor with Pressure Resistant Explosion-proof Type Metal Protection Tube

This type is suitable for use in dangerous places where explosive gas may occur such as petroleum refining/petrochemical plants.

RBG: Resistance Thermometer Sensor with Pressure Resistant Explosion-proof Type Metal Protection Tube image



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