IEC 60068 Environmental Testing

IEC 60068 Environmental Testing is an internationally recognized standard developed by the International Electrotechnical Commission and is a collection of methods for environmental testing of electronic equipment, components and electromechanical products to assess their performance and survivability under conditions such as transport, storage, operating environments, extreme cold and extreme heat.

Temperature change test design

The Na, Nb, and Nc tests consist of alternating high and low temperature cycles, with a definite transfer from one temperature to the other. The adjustment run from the laboratory environment to the first adjustment of the temperature, to the second adjustment of the temperature, and then back to the laboratory environment is considered a test cycle

Test Na: Rapid change of temperature with prescribed time of transfer

This test measures the ability of components, equipment or other items to withstand rapid changes in ambient temperature. The appropriate exposure time depends on the nature of the sample. The sample shall be in a state of unpacked, closed, ready for use or otherwise specified in the relevant specifications. By alternating exposure to low and high temperatures, the specimen is exposed to rapid changes in temperature in air or an appropriate inert gas

Testing procedure

Environmental testing equipment - high and low temperature test chamber
Two separate chambers or a rapid temperature change rate chamber can be used. If two chambers are used, one low temperature chamber and one high temperature chamber, the location should allow the sample to be transferred from one chamber to the other within a specified time. Manual or automatic transmission methods can be used.
These chambers shall be able to maintain the atmosphere at an appropriate temperature in any area where the specimen is placed.
After the specimen is inserted, the air temperature shall be within the specified tolerance for no more than 10% of the exposure time.

Test cycle

The test specimen shall be exposed to the cold temperature, T_A.
The temperature, T_A, shall be maintained for the specified period t₁. t₁, includes an initial time, not longer than 0,1 t₁ for temperature stabilization of the air temperature in the chamber (see7.2.1).
Note 1  The exposure time is measured from the moment of insertion of the specimen into the chamber.
The specimen shall then be exposed to the hot temperature, T_B, in a period, t₂, which should not be more than 3 min.
T₂ shall include the time need for the removal from one chamber and the insertion into thesecond chamber as well as any dwell time at the ambient temperature of the laboratory.
Note 2 For specimens with a large mass, the transfer time from one chamber to another may be increased asl specified in the relevant standard or specification.
T_B shall be maintained for the specified period, t₁. t, includes an initial time, not longer than 0,1 t₁, for temperature stabilization of the air temperature in the chamber (see 7.2.1).
Note 3 The exposure time is measured from the moment of insertion of the specimen into the chamber.
For the next cycle the specimen shall be exposed to the cold temperature, T_A, in a transfer time, t₂, which shall not be more than 3 min.
The first cycle comprises the two exposure times, t₁, and the two transfer times, t₂ (see Figure 2).
At the end of the last cycle the specimen shall be subjected to the recovery procedures

Test Nb: Change of temperature with specified rate of change

This test determines the ability of a component, device, or other item to withstand and/or work when the ambient temperature changes. The sample shall be in an unpacked, closed, ready for use or other condition specified in the relevant specifications. The sample is exposed to a specified temperature in a room changing at a controlled rate, exposing it to temperature changes in the air. During this exposure, the performance of the sample can be monitored.

Testing procedure

The laboratory shall be designed in such a way that the working space in which the test specimen is placed can be temperature cycled in the following manner:
(1) can maintain the low temperature required by the test;
(2) can maintain the high temperature required by the test;
(3) The rate of change required to carry out the test from low temperature to high temperature or vice versa at the desired rate of change.

Test cycle

The air temperature in the chamber shall then be lowered to the specified low temperature,T_A, at the specified rate (see Figure 3).
After temperature stability in the chamber has been reached, the specimen shall be exposed to the low temperature condition for the specified period, t₁.
The air temperature in the chamber shall then be raised to the specified high temperature, T_B at the specified rate (see Figure 3).
After temperature stability in the chamber has been reached, the specimen shall be exposed to the high temperature condition for the specified period, t₁.
The air temperature in the chamber shall then be lowered to the value of the laboratoryambient temperature, +25 C +5 K, at the specified rate (see Figure 3).
This procedure constitutes one cycle.

Test Nc: Rapid change of temperature, two-fluid-bath method

Environmental testing equipment-thermal shock test chamber

Two temperature chambers, a low greenhouse and a high greenhouse, should enable the sample to be easily submerged and quickly transferred from the low to the high temperature zone.
The low temperature bath shall contain liquid at the lower temperature, T_A, stated in thel relevant specification. If no temperature is stated the liquid shall have a temperature of 0 °C.
The bath for the high temperature shall contain liquid at the upper temperature, T_B, as required by the relevant specification. If no temperature is stated the liquid shall have a temperature of 100 °C.
The baths shall be so constructed that at no moment during the test shall the temperature ofl the cold bath rise more than 2 K above T_A or the temperature of the warm bath fall more than 5 K below Tв.
The liquids used for the test shall be compatible with the materials and finishes used in the manufacture of the specimens.
Note The rate of heat transfer will depend upon the liquids used and will affect the severity of the test for a givenltemperature range. In special cases, the relevant specification should specify the liquids to be used.

Test cycle

The specimen under test while being at the ambient temperature of the laboratory shall be immersed into the cold bath containing liquid at the temperature T_A as stated in the relevant specification.
The specimen shall be maintained immersed in the cold bath for the appropriate period, t₁.
The specimen shall then be removed from the cold bath and immersed in the hot bath containing liquid at the temperature T_B as stated in the relevant specification.  The transfer time t₂ shall be as stated in the relevant specification.
The specimen shall be maintained immersed in the hot bath for the appropriate period, t₁.
The specimen shall then be removed from the hot bath.  
The period t₂ between removal fromthe hot bath and immersion in the cold bath shall be as specified in the relevant specification.
One cycle consists of two immersion times, t₁, and two transfer times, t₂ (see Figure 4).
At the end of the last cycle, the specimen shall be subjected to the recovery procedure.