Environmental testing—Part 3: Supporting documentation and guidance—Measurements in temperature chambers for tests A (Cold) and B (Dry heat) (with load)
Environmental testing - Part 3: Supporting documentation and guidance - Meas-urements in temperature chambers for tests A (Cold)and B (Dry heat) (with load)
1 Scope
This part of IEC 60068 specifies a uniform and reproducible method of confirming that temperature test chambers conform to the requirements specified in the climatic test procedures of IEC 60068-2-1 and IEC 60068-2-2, when loaded with either heat-dissipating or non heat-dissipating specimens under conditions which take into account air circulation inside the working space of the chamber. This document is intended primarily for users when conducting regular chamber performance monitoring.
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 2424.5-2021, Environmental testing - Part 3-5: Supporting documentation and guidance - Confirmation of the performance of temperature chambers
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:
——IEC Electropedia: available at http://www.electropedia.org/
——ISO Online browsing platform: available at http://www.iso.org/obp
3.1
test specification
procedure applied to test chambers with or without forced air circulation, suitable for a wide range of chamber sizes
Note: A summary of test conditions in IEC 60068-2-1 and IEC 60068-2-2 is given in Table 1; conditions including sudden change of temperature have been removed from earlier versions of these documents.
3.2
confirmation method
specified method of making continuous measurements in order to establish whether the performance of a test chamber conforms to the requirements detailed in IEC 60068-2-1, test A and/or IEC 60068-2-2, test B
3.3
routine monitoring method
specified method of making measurements, continuously or at intervals, to ensure that the test chamber performance is being maintained
3.4
test load
test specimen that is installed in the test chamber for the confirmation measurements
Note: The test load is defined by geometric dimensions and by thermal properties.
3.5
artificial load
test load made in accordance with IEC 60068-3-7 with dimensions and thermal properties related to the geometric dimensions and thermal capacity of the specimens intended to be
tested in the chamber
Note: Table 2 provides values for an artificial load and an example is given in Figure 1.
4 Measuring system
4.1 General description
The system used for the confirmation and routine monitoring measurements, either built-in or independent of the chamber, should comply with the following requirements. Measurement devices other than those listed may be used when their performance is shown to be technically equivalent or when practical concerns require alternative techniques. Deviations from these requirements shall be documented.
4.2 Temperature
4.2.1 General
Platinum resistance thermometers (in accordance with IEC 60751) or thermocouples (in
accordance with IEC 60584-1) should be used.
4.2.2 Temperature sensor
In a temperature range from −200 °C to +650 °C the sensor measurement uncertainty should be in accordance with class A of IEC 60751.
4.3 Humidity
4.3.1 General
The humidity test is required for confirmation of IEC 60068-2-2 tests only.
Place the independent humidity sensor as near as practical to the centre of the working space.
Types of humidity monitoring sensors are described in 4.4 of GB/T 2424.6-2021.
4.3.2 Humidity sensor
Sensor measurement uncertainty should not exceed ±3 % RH.
4.4 Wall emissivity
Emissivity of the chamber enclosure should be in accordance with IEC 60068-3-1.
4.5 Air velocity
4.5.1 General
An airflow sensor should be installed such that the maximum air velocity impinging on the load can be monitored.
4.5.2 Air velocity sensor
The air velocity sensor measurement uncertainty should be compatible with IEC 60068-2-1 and 60068-2-2 tolerances.
4.5.3 Air velocity sensor response time
The air velocity sensor response time should be greater than 5 s to avoid any influence on it by airflow fluctuation.
4.6 Recording device
For confirmation monitoring, data should be recorded at least once per minute. For routine monitoring, data should be recorded at least once every 5 min. For the purpose of chamber verification, the device utilized for recording data should be independent of the chamber control system.
