Study of Technology for Detecting Pre-Ignition Conditions of ... - NIST

probably not be easy to market for use near food. Ionintion detectors also provide much greater
sensitivity than would be required for range use. Condensation nuclei type smoke detectors
would respond properly to smoke levels, but these also are very sensitive and need humidification
components that make the device overly complex. Electrostatic detectors measure the charge on
soot particles, but they may not work well with. smoke that is not a product of mmbustion.
Photoelectric detectors require only a light source and a light receiver to detect scattered
or attenuated light. The moderate simplici~ of this tectiolo~ makes it attractive for potential
use on ranges. A problem with point type photoelectric smoke detectors is that they require the
smoke to come to the detector through ambient flows or diffhsion. A point type detector installed
on a range would not see smoke until too late because the buoyant plume carries smoke up and
away from the range. A point type dete~or would function well in the range hood or installed
somewhere above the range, but those locations are outside the scope of this project. Smpling
type photoeletic detectors have similar di~lcultim as the wndemation detetiors because they
require a flow system to carry the air and smoke inside.
bother kind of photoe}e~ic smoke detector is the beam type which directs light from
an emitter diode into the air and receives scattered light back from particles onto a detector diode.
If particles from smoke reach a high enou@ density, a tieshold level of received light is attained
and the detector signals a danger condition. Complications with this device are the potential
inadvefient blockage of the detmor and large scale reflection of li@t back to the detector by
nearby objects. These issues are ad&msable through a design process.
Another p~icle-bmed detector is the piemeletic microbalance mass sensor which
detects the chmging particle loading on an oscillating quartz crystal by its frequency change, but
it responds to only smaller particles and bewmes Ioadd easily. Simikar in concept to the l?TEt
spectrometer used in this project’s experiments is the monitoring of specific infrared spectral
bands to detect various gases.
Chemical detectors are a more recent addition to detector technology. 6as sensors using
tin oxide (Sn02) are sensitive to carbon monoxide as well as oxidizable hydrocarbons, so either
would be detected if present as food ignition approaches. Platinum doping allows the sensor to
operate at room temperature instead of 300 ‘C. Catalytic sensors heat when in contact with
specific chemical gases, but the catalyst can become poisoned, and it can be confimed by mixtures
of gases. Elemochemical sensors change their eletical properties when an impinging gas causes
a reaction, but these sensors are usually slow and require high tempera~res.
TemperaWre could be monitored by many methods including infrared emission, but
sophisticated thermometry is expensive. Temperature technology in the form of thermocouples,
thermistors, or R~s (rwisWce temperature devices) is inexpemive and versatile. One or more
of these devices could be used in conjunction with a smoke detection device to prevent false
alarms by providing additional checks on the possible approacKlng fire situation. Since sensing
of a tempera~re th=kold would be most appropriate, thermistors, which are very sensitive to
changes, would probably not be the best choice. The platinum in RTDs can make their cost
prohibitive depending on the size of the device. Themowuples remain an effective and
inexpensive metiod of tiemome~.
The mmbination of smoke sensing and temperature sensing devices in a single dete~or
requires a microprocessor of some sort to logically inte~ret the incoming sensor information.
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