CCT Chamber - ACC29 Refrigeration - how it works
CCT Chamber - ACC29 Refrigeration
This optional accessory comprises of a separate free-standing air temperature conditioning unit (ATCU), capable of refrigerating its atmosphere from ambient to -20°C/-4°F (lower temperatures can be quoted on request). This atmosphere is circulated at high velocity between the ATCU and the CCT chamber to which it is connected, to create a refrigerated, homogeneous climate inside the CCT chamber.
The control system fitted to Ascott CCT chambers enables the user to program whether refrigeration is conducted alone, or in sequence with other climates, to form a cyclic corrosion test, for automatic execution by the chamber.
Compressed air inlet
Compressed air from a separate compressed air supply is required for the chamber in this mode of operation. This is used to open and close the pneumatically actuated butterfly valves which connect the CCT chamber to the ATCU. The compressed air supply should be clean, dry and oil free, pressurised to within the limits 4.0 to 6.0 bar (58 to 87 P.S.I.). Consumption is minimal.
Where a local supply is either unavailable or unsuitable Ascott offer an independent oil free air compressor as an optional accessory (ref.: ACC04). This requires connection to its own single phase electrical supply.
Air Temperature Control Unit (ATCU)
The ATCU is a free standing climate controlled chamber, which is controlled by and connected to the CCT chamber. When required to do so by the CCT program being run, the ATCU will automatically refrigerate air to the required, user adjustable, set temperature. This air is circulated to and from the CCT chamber, by a powerful air circulation fan/blower, via insulated flexible hoses. The ATCU is also connected to the CCT chamber by an umbilical, which provides electrical and pneumatic signals from the CCT chamber control system, to control the operation of the ATCU. The ATCU requires connection to its own 3 phase electrical power supply.
Two pneumatically actuated butterfly valves, automatically open when the CCT program being run requires conditioned air from the ATCU. These butterfly valves close automatically in all other modes of operation, to seal the chamber.
Insulated Flexible Hoses
Two insulated flexible hoses duct the atmosphere between the CCT chamber and the ATCU.
Forming the centre-piece of the ergonomically designed control panel is a state of the art, touch-screen, Human Machine Interface (HMI). It is here that the user controls and monitors the various chamber functions. The HMI incorporates alpha-numeric text messaging and digital displays of chamber variables such as temperature, humidity and time. Also included is a useful trend logging facility. This generates a graphical display of set values for temperature and humidity, over a 72 hour time period, and compares this to the actual temperature and humidity achieved inside the chamber, over the same period.
All chamber control panels incorporate an emergency stop and other safety facilities.
A floor level drain is required to remove any condensate from inside the chamber. This may arise due to the formation of frost at or below freezing temperatures, which will need to drain to waste on thawing.
If access to a floor level drain is not possible or inconvenient, Ascott offer an optional accessory (ref; ACC20) comprising of a waste water trough and pump, which locates on the floor behind the chamber. Condensate from the chamber drain outlet is directed into this. When the holding tank becomes full, the condensate will automatically be pumped out by a marine specification pump. This will discharge waste water to a remote drain or effluent tank located up to 10M/30ft away horizontally and up to 3M/10ft vertically. ACC20 is not suitable for chambers fitted with the SO2 gas dosing optional accessory (ref; ACC46) due to the possible existence of H2SO4 in the condensate.
The chamber canopy is effortlessly opened/closed using pneumatic cylinders, which are activated at the touch of a button on the control panel. An automatic purge facility is incorporated to minimise the risk of corrosive salt spray escaping into the laboratory when the chamber is opened.
Strategically located sensors, mounted inside the chamber and air saturator, monitor the climate continuously and convey this information to the Human Machine Interface (HMI), where it is displayed digitally at the control panel. Temperatures are monitored by PT100 precision temperature sensors and displayed to a resolution of 0.1°C. CCT chambers are also equipped with a special design of corrosion resistant humidity sensor. This measures the relative humidity electronically inside the chamber and displays this at the HMI as %RH to a resolution of 1%RH.
Test samples are accommodated within the chamber generally by placing on, or by suspending beneath, sample racks. A full set of sample racks are provided as standard with each new chamber (see chamber data sheets for quantity) in a choice of styles. Additional sample racks are available as optional accessories, if required, as is a reinforced false floor (ref; ACC19) for supporting large/heavy test samples directly on the chambers internal base.
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