GB/T 30121-2026 Industrial platinum resistance thermometers and platinum temperature sensors
1 Scope
This document specifies the requirements, in addition to the resistance versus temperature relationship, for both industrial platinum resistance thermometers (later referred to as "thermometers") and industrial platinum resistance temperature sensors (later referred to as "platinum resistors") whose electrical resistance is derived from defined functions of temperature.
Values of temperature in this document are in terms of the International Temperature Scale of 1990, ITS-90. A temperature in the unit °C of this scale is denoted by the symbol t, except in Table A.1 where the full nomenclature t90/°C is used.
This document applies to platinum resistors whose temperature coefficient α, defined as
(1)
is conventionally written as α = 3.851 X 10-3 °C-1.
where
R100 is the resistance at t = 100 °C and;
R0 is the resistance at t = 0 °C.
This document covers platinum resistors and thermometers for the temperature range −200 °C to +850 °C with different tolerance classes. It can also cover particular platinum resistors or thermometers for a part of this temperature range.
For resistance versus temperature relationships with uncertainties less than 0.1 °C, which are possible only for platinum resistors or thermometers with exceptionally high stability and individual calibration, a more complex interpolation equation than is presented in this document can be necessary. The specification of such equations is outside the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 18404-2022 Mineral insulated metal-sheathed thermocouple cables and thermocouples
IEC 60068-2-6 Environmental testing - Part 2-6: Tests - Test Fc: Vibration (sinusoidal)
Note: GB/T 2423.10-2019, Environmental testing - Part 2:Test methods - Test Fc: Vibration (sinusoidal) (IEC 60068-2-6: 2007, IDT)
IEC 61152 Dimensions of metal-sheathed thermometer elements
Note: GB/T 19900-2005, Dimensions of metal-sheathed thermometer elements (IEC 61152:1992, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
- ISO Online browsing platform: available at https://www.iso.org/obp
- IEC Electropedia: available at https://www.electropedia.org/
3.1
platinum resistor
resistor made from a platinum wire or film with defined electrical characteristics, embedded in an insulator (in most cases glass or ceramic), designed to be assembled into a platinum resistance thermometer or into an integrated circuit
3.2
platinum resistance thermometer; PRT
temperature-responsive device consisting of one or more sensing platinum resistors within a protective sheath, internal connecting wires, and external terminals to permit connection of electrical measurement instruments
Note 1: Mounting means and connection heads can be included. Not included is any separable protection tube or thermowell.
Note 2: Also referred to as an "industrial platinum resistance thermometer" (excluding secondary instruments).
3.3
nominal resistance
expected resistance R0 of a platinum resistor or thermometer at 0 °C, declared by the supplier and shown in the thermometer marking, usually rounded to the nearest ohm
Note: Platinum resistors are often characterized by their nominal resistance. For example, a platinum resistor with R0 = 100 Ω is often referred to as a Pt100.
3.4
terminals
termination of the connections supplied with the platinum resistance thermometer
Note: Typical types of terminals are:
- screws or clamps on the terminal socket,
- pins of fixed connectors,
- open ends of fixed cables or equivalents.
3.5
temperature-sensitive length
length of the thermometer whose temperature directly influences the resistance measured
Note: Usually, the temperature-sensitive length is related to the length of the platinum resistor.
3.6
minimum immersion depth
immersion depth at which the change from the calibration at full immersion does not exceed 0.1 °C
3.7
tolerance
maximum allowable deviation of R(t) measured at temperature t from the nominal resistance versus temperature relationship
Note: Expressed as Δt(t) in °C
3.8
dielectric strength
maximum voltage between all parts of the electric circuit and the sheath of the thermometer or, in the case of a thermometer with two or more sensing circuits, between two individual circuits that the thermometer can withstand without damage
3.9
insulation resistance
electrical resistance measured between any part of the electric circuit and the sheath at ambient or elevated temperatures and with a specified measuring voltage (AC or DC)
3.10
self-heating
increase of the temperature of the platinum resistor or of the platinum resistor in a thermometer caused by the dissipated energy of the measuring current
3.11
self-heating coefficient
temperature rise due to dissipated energy by measuring current in a resistor
Note: Expressed with the unit °C/mW
3.12
thermal response time
time a thermometer takes to reach a specified percentage of a step change in temperature
3.13
thermoelectric effect
effect of inducing electro-motive force (abbreviated by e.m.f hereafter) caused by different metals used in the electric circuit of the thermometer and by thermoelectric inhomogeneity of the internal leads at the conditions of temperature gradients along the leads
3.14
hysteresis
resistance difference at the middle of the temperature range between before and after exposing the thermometer to the lower and upper limit of the temperature range
3.15
expanded uncertainty
quantity defining an interval about the result of a measurement that can be expected to
encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand
Note: For reference, see 3.16.
3.16
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded uncertainty
Note: Coverage factor, k, is typically in the range 2 to 3. In this document, k = 2 is chosen, the confidence level of which is 95 %. Refer to Bibliography [1].
4 Characteristics
4.1 General
The nominal resistance versus temperature relationship for platinum resistors and thermometers and their tolerance class are standardized. This specification is applied to a sensing platinum resistor at its connecting points and to a complete thermometer at its terminals.
In the case of two-wire connections (see 5.5), the resistance values of the leads between the connecting point of the platinum resistor and the terminals shall be considered. They shall be subtracted from measured resistances. In some cases, it is also advisable to consider the temperature coefficient of the lead wires, the geometrical characteristics of the wires, and the temperature distribution along their length. This information may be supplied to users as additional information (refer to Clause 7).
4.2 Nominal resistance versus temperature relationship
The resistance versus temperature relationships used in this document are given in Formula (2) and Formula (3):
For the range −200 °C to 0 °C:
GB/T 30121-2026 Industrial platinum resistance thermometers and platinum temperature sensors
1 Scope
This document specifies the requirements, in addition to the resistance versus temperature relationship, for both industrial platinum resistance thermometers (later referred to as "thermometers") and industrial platinum resistance temperature sensors (later referred to as "platinum resistors") whose electrical resistance is derived from defined functions of temperature.
Values of temperature in this document are in terms of the International Temperature Scale of 1990, ITS-90. A temperature in the unit °C of this scale is denoted by the symbol t, except in Table A.1 where the full nomenclature t90/°C is used.
This document applies to platinum resistors whose temperature coefficient α, defined as
(1)
is conventionally written as α = 3.851 X 10-3 °C-1.
where
R100 is the resistance at t = 100 °C and;
R0 is the resistance at t = 0 °C.
This document covers platinum resistors and thermometers for the temperature range −200 °C to +850 °C with different tolerance classes. It can also cover particular platinum resistors or thermometers for a part of this temperature range.
For resistance versus temperature relationships with uncertainties less than 0.1 °C, which are possible only for platinum resistors or thermometers with exceptionally high stability and individual calibration, a more complex interpolation equation than is presented in this document can be necessary. The specification of such equations is outside the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 18404-2022 Mineral insulated metal-sheathed thermocouple cables and thermocouples
IEC 60068-2-6 Environmental testing - Part 2-6: Tests - Test Fc: Vibration (sinusoidal)
Note: GB/T 2423.10-2019, Environmental testing - Part 2:Test methods - Test Fc: Vibration (sinusoidal) (IEC 60068-2-6: 2007, IDT)
IEC 61152 Dimensions of metal-sheathed thermometer elements
Note: GB/T 19900-2005, Dimensions of metal-sheathed thermometer elements (IEC 61152:1992, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
- ISO Online browsing platform: available at https://www.iso.org/obp
- IEC Electropedia: available at https://www.electropedia.org/
3.1
platinum resistor
resistor made from a platinum wire or film with defined electrical characteristics, embedded in an insulator (in most cases glass or ceramic), designed to be assembled into a platinum resistance thermometer or into an integrated circuit
3.2
platinum resistance thermometer; PRT
temperature-responsive device consisting of one or more sensing platinum resistors within a protective sheath, internal connecting wires, and external terminals to permit connection of electrical measurement instruments
Note 1: Mounting means and connection heads can be included. Not included is any separable protection tube or thermowell.
Note 2: Also referred to as an "industrial platinum resistance thermometer" (excluding secondary instruments).
3.3
nominal resistance
expected resistance R0 of a platinum resistor or thermometer at 0 °C, declared by the supplier and shown in the thermometer marking, usually rounded to the nearest ohm
Note: Platinum resistors are often characterized by their nominal resistance. For example, a platinum resistor with R0 = 100 Ω is often referred to as a Pt100.
3.4
terminals
termination of the connections supplied with the platinum resistance thermometer
Note: Typical types of terminals are:
- screws or clamps on the terminal socket,
- pins of fixed connectors,
- open ends of fixed cables or equivalents.
3.5
temperature-sensitive length
length of the thermometer whose temperature directly influences the resistance measured
Note: Usually, the temperature-sensitive length is related to the length of the platinum resistor.
3.6
minimum immersion depth
immersion depth at which the change from the calibration at full immersion does not exceed 0.1 °C
3.7
tolerance
maximum allowable deviation of R(t) measured at temperature t from the nominal resistance versus temperature relationship
Note: Expressed as Δt(t) in °C
3.8
dielectric strength
maximum voltage between all parts of the electric circuit and the sheath of the thermometer or, in the case of a thermometer with two or more sensing circuits, between two individual circuits that the thermometer can withstand without damage
3.9
insulation resistance
electrical resistance measured between any part of the electric circuit and the sheath at ambient or elevated temperatures and with a specified measuring voltage (AC or DC)
3.10
self-heating
increase of the temperature of the platinum resistor or of the platinum resistor in a thermometer caused by the dissipated energy of the measuring current
3.11
self-heating coefficient
temperature rise due to dissipated energy by measuring current in a resistor
Note: Expressed with the unit °C/mW
3.12
thermal response time
time a thermometer takes to reach a specified percentage of a step change in temperature
3.13
thermoelectric effect
effect of inducing electro-motive force (abbreviated by e.m.f hereafter) caused by different metals used in the electric circuit of the thermometer and by thermoelectric inhomogeneity of the internal leads at the conditions of temperature gradients along the leads
3.14
hysteresis
resistance difference at the middle of the temperature range between before and after exposing the thermometer to the lower and upper limit of the temperature range
3.15
expanded uncertainty
quantity defining an interval about the result of a measurement that can be expected to
encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand
Note: For reference, see 3.16.
3.16
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded uncertainty
Note: Coverage factor, k, is typically in the range 2 to 3. In this document, k = 2 is chosen, the confidence level of which is 95 %. Refer to Bibliography [1].
4 Characteristics
4.1 General
The nominal resistance versus temperature relationship for platinum resistors and thermometers and their tolerance class are standardized. This specification is applied to a sensing platinum resistor at its connecting points and to a complete thermometer at its terminals.
In the case of two-wire connections (see 5.5), the resistance values of the leads between the connecting point of the platinum resistor and the terminals shall be considered. They shall be subtracted from measured resistances. In some cases, it is also advisable to consider the temperature coefficient of the lead wires, the geometrical characteristics of the wires, and the temperature distribution along their length. This information may be supplied to users as additional information (refer to Clause 7).
4.2 Nominal resistance versus temperature relationship
The resistance versus temperature relationships used in this document are given in Formula (2) and Formula (3):
For the range −200 °C to 0 °C:
