A photoelectric cell in the exhaust stream measures the visible light obscuration, which is caused by the smoke produced during the test.
(A photoelectric cell in the exhaust stream; measures; the visible light obscuration, which is caused by the smoke) (the visible light obscuration; is caused; by the smoke) (the smoke; produced; T:during the test)
A photoelectric cell in the exhaust stream the visible light obscuration the smoke
measures is caused produced
the visible light obscuration, which is caused by the smoke
by the smoke
T:during the test