Overview
The Auto Sash Controls are designed to close the Fume Cupboard Sash automatically when the operator is not present at the Fume Cupboard to maximise the Energy Saving from the VAV control system and to give the additional safety to personnel walking past the Cupboard.

The control system comprises of the following parts:-

Personnel sensor – To detect the presence of the user. The Sash will not automatically close when the user is present at the Cupboard. The sensor will re-learn the background at regular intervals so will detect if a stool or other items are left in the detection area and incorporate it into the background.

Alarm Panel – Red LED / Pushbutton – gives visual indication of a fault and also used to reset once the fault has been cleared. There are two fault conditions:-

Sash closing time – The control system monitors the time the sash takes to close, if the sash has not closed in a preset time the fault indicator will illuminate and the output to the sash drive will be disabled. Once the fault has been checked and cleared pressing the alarm panel reset pushbutton will reset the controls.

Sash obstruction – The control system has a safety light curtain sensor that checks the Sash opening is clear before the drive operates. If an obstruction is detected the fault indicator will illuminate and the output to the Sash drive will be disabled. Once the fault has been checked and cleared pressing the alarm panel reset pushbutton will reset the controls.

Sash sensor – The sash control system uses a Safety Light Curtain to detect that the opening below the sash is clear before the sash is driven closed. The safety light curtain consists of an Infra Red transmitter on one side of the Fume Cupboard inner chamber and an Infra Red detector on the opposite side of the inner chamber. The Transmitter and Receiver are approx 710mm high and have multiple close positioned LED-s to detect small objects - the Light Curtain will also detect Glass objects.

Sash Low Switch – used to detect that the Sash is closed.

Sash Drive Unit – A geared motor and clutch assembly used to drive the Sash. The motor is a 24v DC geared motor complete with a speed controller to adjust the speed of the closing Sash. The clutch assembly is connected to the motor and is only energised when the sash is driving – this ensures that the Sash and the Sash mechanism are disconnected from the drive when the operator is present at the Fume Cupboard and the Sash can be manually opened or closed with no additional resistance to the movement.

Method of Operation
When the operator stands in front of the Fume Cupboard the Personnel Detector will see the operator and reset the controls so that the Sash drive is mechanically disconnected via the Clutch mechanism. The operator can then operate the sash manually in the normal manner.

When the operator leaves the Fume Cupboard the Personnel Detector will see this and will initiate a run-down time (adjustable on site). At the end of this time delay the sash will drive to the closed position only if the Safety Light Curtain detects that there are no objects present that could be struck by the moving sash. If any objects enter the field of the Safety Light Curtain when the Sash is driving closed or the operator returns to the Fume Cupboard then the Sash drive will disconnect and the Sash will stop.

As an additional safety feature the controls include a delay timer which is set to the time period that the sash is expected to close from the fully open position. If for any reason the Sash does not reach the sash closed switch within this time period then the drive mechanism will lock out and will activate the illuminated pushbutton on the alarm panel. The Unit will remain locked out until the problem is resolved and the illuminated alarm button is pressed – during this time the sash can be operated manually as normal.