In all climatic testing cabinets there is inevitably a variation in temperature between different points within the interior. These temperatures will also fluctuate over time.
While miniscule, these variations and fluctuations have to be taken into account as part of any rigorous climatic testing programme. This can be achieved by locating temperature sensors at different points within the cabinet and then calibrating the results.
Our standard CTS chambers employ a central rear fan, which circulates conditioned air from the base of the chamber so it rises up through the test area. Air flow rates are high to be consistent with the best thermal performance. Chambers that are adapted to sit on top of a shaker reverse this air flow as the shaking interferes with the normal upward circulation of air.
The variation is the maximum deviation of the average temperatures in the corners of the usable space compared to the average temperature at the centre of the usable space.
The temperature sensors within our standard CTS chambers are located in accordance with industry standard IEC 60068-3-5 guidelines. We can move theses sensors to different locations within the cabinet to match a customer’s requirement, as long as any adjustment falls within these guidelines.
All CTS chambers sized 200 litres and above are able to measure temperature at the point where the air enters the test space – a location that usually reflects the conditions at the centre of the usable space for CTS cabinets. Alternatively, sensors can be located at the point where the air exits the test space. The ability to use either inlet or outlet temperature measurements allows greater flexibility in testing large mass or test items with heat output.
For chambers up to and including 2000 litre test space the IEC60068-3-5 guidelines stipulate there should be nine points of measurement – that is eight in the corner areas and one at the centre point. The requirement for larger chambers is that 15 sensors be placed at different points within the cabinet.
To achieve compliance with the international ISO17025 standard all the multiple points – whether it be nine or 15 – need to be included in the calibration.
When customers receive a CTS chamber, they are supplied with details of the fluctuation and variation within the empty test space. These figures are always given for the chamber in a steady state condition. When the chamber is received, stabilization time is required for it to return to this condition.
We can also provide our customers with the fluctuation and variation measurements relating to a when a specific test specimens is in place.
To provide this we require:
Calculating specific results can be complex as range of factors, such as the mass of the specimen, surface area, shape, product heat output, materials of construction, internal voids, will affect results.
During the chambers operational life, which is likely to be many years, adjustments that will ensure accurate temperature calculations can be carried out by an approved service engineer.
If you would like to discuss any of the details above or any testing requirements you may have, please call us on 01223 269400 for an informal conversation.