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New JTM standards for temperature test chambers - Methods of testing and indicating performance

New JTM standards for temperature test chambers

-          Methods of testing and indicating performance    (Part)


 

1,  Trends in standards for environmental test equipment

2,  New test and indication methods for performance

   Table 1 presents an overview of the major revisions to the standards.

       Table 1 Principal changes in the new JTM standards

 

 

Current standards 

 

New standards

Comments

Method of indicating

performance

 

Range of temp. fluctuation

Temp. fluctuation

 Method of confirming performance also

 changed

Temp. uniformity

Temp. gradient, Temp. variation in space

Method of confirming performance also

 changed

Heating/cooling time

Temp. rate of change

Method of confirming performance also

 changed

Method of confirming performance

 

Distance of working space

Space excluding 1/6 of distance from inner walls

Space excluding 1/10 of distance from inner walls

Minimum values

 specified for different test chamber volumes

Range of temp. fluctuation

Measurement point: single point at center of chamber Calculation method: take the difference between average high and average low temps, divide by two, and express as ± value

Measurement points: 9 points (chamber center and 8 corners) Calculation method: take the highest value of the standard deviation among all of the measurement points, double it, and express as ± value.

 

Temp. uniformity

 

Concept: Difference between center of chamber and 8 corner points

 

Concept: Difference between center of chamber and 8 corner points, and difference among corners

 

Heating/cooling time

 

Definition: Time required to reach max/min temp. from ambient temp. Expression: n1 to n2, x minutes

 

Definition: Rate of temp. change during one minute for specified times Expression: K/minute or /minute

 

Time to reach temp. extreme conforms to prior heating/cooling time

 

2-1 Working space

The working space is a test chamber area that can maintain specified temperature conditions

within an allowable range. The test chamber

2-1 Working space

The working space is a test chamber area that can maintain specified temperature conditionswithin an allowable range. The test chamber generally takes the shape of a rectangular box, and

the working space is composed of the area surrounded by the shaded surface shown in Fig.1. The

distance from each of the wall surfaces surrounding the working space to the next corresponding

chamber surface shall be termed as L1, L2, and L3, respectively. Current standards define the

working space as the space between the surrounding walls excluding the area adjacent to the

walls composed of a distance divided by 6 from the total surface distance, expressed as L1/6,

L2/6, and L3/6. The new standards define the working space as the space between the

surrounding walls excluding the area adjacent to the walls composed of a distance divided by 10

from the total surface distance, expressed as L1/10, L2/10, and L3/10. However, since it is

necessary to consider the effect of thermal emissions in the space between the inner walls of the

test chamber and the test specimens, the distance from the inner walls must be specified as a

minimum value according to the volume of each test chamber.


2-2
Range of temperature fluctuation

The range of temperature fluctuation in the current standards is defined as the difference between the average high temperature and the average low temperature at the center of the test chamber. The new standards refer to temperature fluctuation, which is defined as the difference between the maximum and minimum temperatures at discretionary points in the working space measured at specified time intervals after the temperature has stabilized. The new standards have set the discretionary points as being at the center and at the corners of the working space.

2-3 Temperature uniformity

2-4 Heating and cooling time

The temperature rate of change is found using the following formula.

Temperature heating rate = t/T1

Temperature cooling rate = t/T2

3  Current standards and the activation of new standards

The current standards will expire five years after the publication of the new standards. The new standards are for the temperature test chamber. At the current stage JIS has not yet published new standards for the temperature and humidity test chamber, and so the new standards for the temperature test chamber will precede those for the temperature and humidity test chamber. As a result, current standards will continue to apply to the temperature and humidity test chamber, and only those contents concerning the temperature test chamber will proceed to application of the new standards.

 4 Coming standards

5 Conclusion

The IEC and JIS standards for temperature test chambers are utilized for all equipment used in environmental testing and are provided for the general use of the user to confirm the performance of test chambers. However, the contents are guidance, and there is a danger that they can be subject to all kinds of interpretations when applied. To eliminate the variations caused by the interpretations among different users, we highly recommend that the new standards published by JTM be confirmed.