CCT Chamber - Controlled Humidity Mode
This mode of operation is provided as standard on all models of Ascott CCT chamber. During this mode, air is drawn from the room in which the chamber is located, and may be heated (subject to user adjustable settings) before being blown into the chamber at a controlled rate. The rate at which this air is blown into the chamber is determined automatically, so that it mixes with an appropriate amount of the existing air inside the chamber. The air inside the chamber, which may have been humidified (also subject to user adjustable settings) mixes with the air blown into the chamber to create a temperature and humidity controlled atmosphere.
In this mode of operation, the chamber can be used to create user adjustable, humidity controlled atmospheres, up to 95%RH, at temperature controlled atmospheres from ambient to +60°C/140°F, and is designed to meet a wide range of international standards for such testing.
The control system fitted to Ascott CCT chambers enables the user to program whether controlled humidity is conducted alone, or in sequence with other climates, to form a cyclic corrosion test, for automatic execution by the chamber.
Air inlet & blower
Fresh air, at ambient temperature and humidity, is drawn from the immediate surroundings of the room in which the chamber is located, by a powerful centrifugal fan type blower. Two blowers are fitted to 2000L size chambers. These blowers deliver air to chamber interior via a heater, ball valve and air diffuser, described below.
An in-line electrical heater is provided to raise the temperature of the incoming ambient air from the blower - if required (determined by the user adjustable chamber set temperature), before delivering this air to the chamber. The heat generated by the blower heater is supplemented by the chamber heating mats (described below) in the controlled humidity mode of operation, to give the chamber a user adjustable temperature range from ambient to +60°C/140°F.
An electrically operated ball valve automatically regulates the amount of air entering the chamber from the blower. This is determined automatically according to the user adjustable humidity level required inside the chamber. A certain pre-determined minimum ball valve aperture ensures that some air is introduced into the chamber continuously. This 'stirs' the chamber atmosphere to maintain good homogeneity.
Larger ball valve apertures are set automatically, whenever dehumidification of the chamber atmosphere is required. It is therefore the balance between the dehumidifying effect of the ball valve aperture and the humidifying effect of the humidity generator that creates and maintains the required humidity level inside the chamber, in this mode of operation. A separate graph confirms the range of humidity and temperature combinations that can be achieved.
In addition, the ball valve automatically closes and seals the blower/heater from the potentially corrosive atmosphere inside the chamber, whenever the blower is not running.
A carefully shaped air diffuser delivers the air from the blower/heater and disperses it evenly throughout the chamber interior.
Set into the bottom of the chamber is a water sump containing a corrosion resistant immersion heater. When the controlled humidity mode of operation is selected, this sump is automatically filled with water, to a pre-determined level, using water taken from the pressurised supply to which the chamber is connected (the same supply that is used to fill and top-up the air saturator used in the salt spray mode of operation). Providing the sump is full of water and the user adjustable set humidity required is higher that the current ambient level inside the chamber, the immersion heater located in the sump will heat. As it heats, it evaporates moisture from the surface of the sump and humidifies the chamber atmosphere above. It is therefore the balance between the humidifying effect of the humidity generator and the dehumidifying effect of the ball valve aperture that creates and maintains the required humidity level inside the chamber, in this mode of operation.
A separate graph confirms the range of humidity and temperature combinations that can be achieved.
Chamber heating mats
Silicone rubber encapsulated electrical heating mats are strategically bonded to the outside surfaces of the bottom and sides of the inner working chamber. If required (determined by user adjustable set temperature), these heater mats operate in conjunction with the blower heater to raise the temperature of the chamber interior. In the air drying mode of operation, the heater mats and blower heater, operating together, give the chamber a user adjustable temperature range from ambient to +60°C/140°F.
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 & 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.
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.
This vents spent air from inside the chamber to atmosphere. The chamber should therefore ideally be located adjacent to an outside wall, and a hole made through the wall to accommodate the exhaust pipe. The end of this pipe should be directed away from persons and property, and be shielded from wind to prevent any disturbance to the conditions inside the chamber.
A floor level drain is required to remove to waste any excess condensate etc. which accumulates over the internal base of the chamber interior. 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.