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

CPSC-LW--95-1I45
The pan area was monitored with several thermocouples. Two thermocouples contacted
the food inside the pan near the center at the bottom and approximately-7 mm (0.3 in) above the
bottom. These themomuples were Omega model number KMQSS-020(G)-12 [stainless-steel
sheathed, O.51 mm (0.020 in) sheath dimeter, K-type (C%romel-Alumel), grounded, 30 cm
(12 in) long]. The temperature inted?ace between the cooking element and pan was measured
with another O.51 mm (0.020 in) sheathed thermocouple. In the case of the electric range, the
themomuple was sandwiched between the centermost ring of the resistive element and the pan.
For the gas range, the thermocouple was located in the outer 2 cm (0.8 in) of the pan diameter
so as not to be in the flame itself. The tiemomuple was bent to cause contact with the pan
bottom. A special washer tiemocouple assembly (a thermocouple designed as a boltable washer)
was attached to the inside of each pan using an 6-32 type screw and nut through a 3.6 mm
(9/64 in) diameter through-hole 1.8 cm (0.7 in) above the bottom (inside) of the pan. This
thermoccmple was Omega model number WTK-6-60 [20 gauge, 0.368 cm (0.145 in) washer
diameter, M3.5 (#6) screw size, K-type (Ckomel-Mumel), 152 cm (60 in) long, glass braid
insulation] and was used to estimate the metal tempera~re at ignition since the ignition location
was most likely the hot metal surface where it interfaced with the food.
Thermocouples were placed at several other locations around the range and range hood
where it would be relatively easy to locate a built-in sensor. The thermocouples were Omega
model no. SA1-K [30 gauge, 0.25 mm (0.01 O in) diameter, K-type (Ckomel-Mumel), 91 cm
(36 in) long, Teflon insulated, self-adhesive backing]. The locations were as follows: 17 cm
from the center of the burner at the 2 and 8 o’clock positions (60 0 and 2400 clockwise from
rear of burner, respectively); mounted on the range hood’s vertical front wall both inside and
outside, centered above the active burneq below the range top under the burner area (electric
only); and on top of the range back, directly behind the burner (gas only). The thermocouple
below the electric range top was only implemented for a few tests.
2.2.2 Laser Attenuation Apparatus
In order to detemine relative aerosol mass mncentiation above the cooking are% two He-
Ne laser attenuation systems were arranged such that the beams passed through the axis of
symmetry of the pan 17.8 cm (7 in) and 27.9 cm (11 in) above the burner surface. The He-Ne
lasers were Melles Griot model number 05-LLR-811, and each generated a beam with 1 mW
power. They were mountd on a vetiical-timslation stand which provided the ability to finely
adjust their position. The tiasmitied light was received by two photodiodes which were mounted
on opticai rods and connected to a power source. The photodiodes (Hamamatsu S 1337- 101 OI3Q,
100 mmz active surface area), operational amplifier circuits, power source box, and mounting!
with connections for power input and signal output were the same as those used by I?itts et al.s
The pre-test output of the devices with unobstmcted laser light was 8-10 V.
2.2.3 Bi-directional Probe
The vertical gas velocity above the cooking
directional probe and a sensitive pressure transducer.
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area was measured through the use of a bi-
The probe was stainless steel with 14.3 mm