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How do the Apollo 65 Ionisation and Optical Smoke detectors work?

How do the Apollo 65 Ionisation and Optical Smoke detectors work?

  2011-08-04         sparksdirect         Safety » Fire Safety

There are extensive articles covering the Aico Domestic Fire / Smoke / Heat alarms, but not too much on one of the most prolific and popular range, the Apollo Smoke Alarms!

We were recently announcing that the Apollo 65 range of Smoke / Heat detectors is back - and here we are with some more useful information concerning how things work in these smoke detectors.

There are several types of detecting methods when it comes to the Smoke and the Heat alarms - the Optical, the Ionisation, and the Heat detection.

Below you can find a little about each one of the first two of these methods - how do they work and how does the Apollo Series 65 work.

How does the Apollo series 65 Ionisation Smoke Detector work?

The sensing part of the Series 65 Apollo ionisation smoke detector consists of two chambers - an open, outer chamber and a semi-sealed reference chamber within.

Mounted in the reference chamber is a low activity radioactive foil of Americium 241 which enables current to flow between the inner and outer chambers when the detector is powered up.

As smoke enters the detector, it causes a reduction of the current flow in the outer chamber and hence an increase in voltage measured at the junction between the two chambers.

The voltage increase is monitored by the electronic circuitry which triggers the detector into the alarm state at a preset threshold.

An externally visible red LED lights up when the detector changes to alarm state. An integrating ionisation detector, suitable for use in areas where transient levels of smoke may be expected, is also available.

How does the Apollo 65 Optical Smoke Detector work?

The Apollo series 65 optical smoke detectors incorporate a pulsing LED located in a chamber within the housing of the detector. The chamber is designed to exclude light from any external source.

At an angle to the LED is a photodiode which normally does not register the column of light emitted by the LED.

In the event of smoke from a fire entering the chamber, the light pulse from the LED will be scattered and hence registered by the photo-diode.

If the photo-diode “sees” smoke on the two following pulses, the detector changes into the alarm state and the indicator LED lights up.

The detector housing is identical to that of the ionisation detector but has an indicator LED which is clear in quiescent state but produces red light in alarm.

[you can get this information from the PDF brochure that Apollo makes it available, Apollo Series 65, and if you want to purchase these devices, please visit the Conventional Smoke Alarms section]