AC'SCENT International Olfactometer:  Definitions

acceptability/unacceptability: Degree to which a stimulus is judged to be favorable or unfavorable. [ASTM E253-97]

acuity: The ability to repeatedly detect or discriminate sensory stimuli. [ASTM E253-97]

accepted reference value: A value that serves as an agreed upon reference for comparison, and which is derived as a consensus value, based on collaborative experimental work under the auspices of a scientific or engineering group. [ISO 5725, part 1]

adaptation (sensory): A decrease in sensitivity to a given stimulus which occurs as a result of exposure to that stimulus. [ASTM E253-97]

anosmia: Lack of sensitivity to olfactory stimuli. [ISO 5492:1992] Absence of the sense of smell.

aroma: Perception resulting from stimulating the olfactory receptors; in a broader sense, the term is sometimes used to refer to the combination of sensations resulting from stimulation of the nasal cavity. See also "odor." [ASTM E253-97]

ascending concentration series: A method of presentation in olfactometry. The assessor (panelist) is presented with a series of dilution ratios (one or two blanks and one odorous presentation) increasing in odor concentration (decreasing dilution ratio). The increase in concentration is usually 2-3 fold. [ASTM E679-91]

assessor: A participant in odor testing (e.g. panelist, panel member, judge, respondent, etc.).

aversion: A feeling of dislike provoking avoidance of a stimulus. [ASTM E253-97]

best estimate criteria: In olfactometry this is the estimated threshold of an individual assessor (panelist) calculated as the geometric mean of the last dilution ratio where the odor was not detected and the next higher concentration (the first dilution ratio where the odor was detected). [ASTM E679-91]

best estimate threshold (BET): The threshold calculated using the best estimate criteria.

bias: The difference between the expectation of the test results and an accepted reference value. [ISO 5725 part 1] Bias is also known as Systematic error.

binary forced choice: A method of olfactometry testing comprising of two presentations, one blank and one with a diluted odor sample. The assessor is forced to select the one with the odor, even if they must guess.

character (quality): Word descriptions of what the odor "smells-like."

detection: The assessor (panelist) is certain one presentation (the odor sample presentation) is different from the two blank presentations.

detection threshold (for a reference material): The odorant concentration which has a probability of 0.5 of being detected under the conditions of the test. [CEN TC264 Draft]

detection threshold (for an environmental sample): the dilution ratio at which the sample has a probability of 0.5 of being detected under the conditions of the test. [CEN TC264 Draft]

determination limit: The odor concentration (or dilution ratio) where 84% of the assessors (panelists) "detect" the odor. [VDI 3881, Part 1]

dilution level: A presentation level on the olfactometer which is set at a specific dilution ratio.

dilution ratio: the ratio of total diluted sample flow volume to the odor sample flow volume. (example: 2 cc/min of sample flow and 20L/min of total flow gives a dilution ratio of 10,000)

DT: see "detection threshold"

D/T: see "detection threshold"

dynamic olfactometer: An olfactometer designed to continuously dilute odorous gases in order to present known dilution ratios to an assessor through a common presentation mask.

dynamic olfactometry: Olfactometry work performed with a dynamic olfactometer.

dysosmia: A dysfunction in the olfactory sense; an impaired sense off smell.

ED50: see "detection threshold (for an environmental sample)"

European Odour Unit: That amount of odorant(s) that, when evaporated into one cubic metre of neutral gas at standard conditions, elicits a physiological response from a panel (detection threshold) equivalent to that elicited by one European Reference Odour Mass (EROM), evaporated in one cubic meter of neutral gas at standard conditions. [CEN TC264 Draft]

European Reference Odour Mass (EROM): The accepted reference value for the European odour unit, equal to a defined mass of a certified reference material. One EROM is equivalent to 123mg n-butanol (CAS 71-36-3) evaporated in one cubic meter of neutral gas. This produces a concentration of 0.040 mmol/mol. [CEN TC264 Draft]

forced-choice method: A method of olfactometry where the assessor is forced to choose which one of the three presentations, one diluted odor sample presentation and two blank presentations, has the odorous sample, even if no difference is found between the three. [ASTM E679-91]

guess: The assessor (panelist) does not perceive a difference between the odorous and blank presentations and therefore makes a "guess" as to which presentation contained the odor.

group threshold: The average threshold of a group of assessors.

hedonic scale: a scale on which liking or disliking of a stimulus is expressed. [ASTM E253-97]

hyperosmia: An increase in olfactory sense. Having a lower odor threshold.

hyposmia: A decrease in olfactory sense. Having an increased threshold (diminished sense of smell).

individual threshold: The detection threshold of one individual assessor.

individual threshold estimate (ITE): The detection threshold of one individual assessor calculated from one dilution series. In olfactometry this value is the best estimate threshold (BET) calculated using the best estimate criteria.

instrument detection limit: The minimum detection limit due to the instrument design.

intensity: The perceived magnitude of a stimulus. [ASTM E253-97]

kakosmia (cacosmia): Dysfunction where there is a presence of unusually unpleasant odors when pleasant odors exist. Usually found in the elderly.

odor / odour: Organoleptic attribute perceptible by the olfactory organ on sniffing certain volatile substances. [ISO 5492] See "aroma."

odorant: A substance that stimulates the olfactory receptors (i.e. a chemical gas). [ASTM E253-97]

odor concentration: The number of European Odour Units in a cubic meter of gas at standard conditions.

Odor Dilution Units (ODU): see "Odor Unit" and "European Odour Unit"

odor panel: see "panel"

odor threshold: see "detection threshold"

Odor Unit (OU): One odor unit is the amount of odorant(s) present in one cubic meter of odorous gas (under standard conditions) at the panel threshold. see "European Odour Unit"

olfactometer: A dilution apparatus which mixes odorous air in specific ratios with odor free air for the presentation to a panel of observers (assessors).

olfactometry: Measurement of the response of assessors to olfactory stimuli. [ISO 5492]

olfactory: Pertaining to the sense of smell. [ISO 5492]

olfactory receptor: Specific part of the olfactory system which responds to an odorant. [after ISO 5492]

olfactory stimulus: That which can excite an olfactory receptor. [ISO 5492, modified]

operator: see "panel leader" or "test administrator"

osmesis: The act of smelling.

panel: A group of assessors used to analyze an odorous sample by olfactometry.

panel leader: The operator of the olfactometer and the person who supervises and instructs the assessors (panelists) during sample analysis. See "test administrator"

panel member: An individual assessor who is part of an odor panel.

panel screening: Procedure used to determine if the performance of a panelist (assessor) is in compliance with selected criteria.

parosmia: a perceived change in ones olfactory sense. A distorted sense of smell encountered with certain brain tumors or in mental illness.

perception: Awareness of the effects of single or multiple sensory stimuli. [ISO 5492]

precision: Closeness of agreement between independent test results obtained under prescribed conditions. [ISO 5725, part 1]

presentation: The presentation of either an odor sample or blank at one dilution level.

presentation face velocity: The velocity of the presentation air at the face of the sampling mask or port.

presentation flow rate: The volumetric flow rate of the presentation air to the assessor.

reaction limit: The odor concentration (or dilution ratio) where 16% of the panelists "detect" the odor. [VDI 3881, Part 1]

recognition: The assessor (panelist) is certain one presentation (the odor sample presentation) is different from the two blank presentations and, further, the assessor can identify or describe the odor.

recognition threshold: The odor concentration which has a probability of 0.5 of being recognized under the conditions of the test. [CEN TC264 Draft]

repeatability (r): Precision under repeatability conditions. [ISO 5725, part 1]

repeatability conditions: Conditions where independent test results are obtained with the same method on identical test material in the same laboratory by the same operator (panel leader) using the same equipment within short intervals of time. [ISO 5725, part 1]

repeatability limit: The value less than or equal to which the absolute difference between two test results obtained under repeatability conditions may be expected to be with a probability of 0.95. [ISO 5725, part 1]

reproducibility (R): Precision under reproducibility conditions. [ISO 5725, part 1]

reproducibility conditions: Conditions where test results are obtained with the same method on identical test material in different laboratories with different operators using different equipment. [ISO 5725, part 1]

reproducibility limit: The value less than or equal to which absolute difference between two test results obtained under reproducibility conditions may be expected to be with a probability of 0.95. [ISO 5725, part 1]

resolution: The dispersion of the distribution of individual threshold estimates (ITE’s) for one sample. Calculated from the "determination limit" (84%ile) and the "reaction limit" (16%ile).

retrospective screening: A procedure for reviewing olfactometry results where results of assessors that show a deviation from normal due to health or specific hypersensitivity or hyposensitivity are remove from the group test average. Removal of an assessor’s results may be based on the standard deviation or the ratio between their individual threshold estimate (ITE) and the group (panel) average.

RT: see "recognition threshold"

R/T: see "recognition threshold"

sample: The sample is the odorous gas sample.

screening: A preliminary selection procedure. [ASTM E253-97]

sensory adaptation: a decrease in sensitivity to a given stimulus which occurs as a result of exposure to that stimulus. [ASTM E253-97]

sensory fatigue: Form of adaptation in which a decrease in sensitivity occurs. [ISO 5492]

smell: See "aroma" or "odor."

standard conditions: Room temperature (293K), normal atmospheric pressure (101.3 kPa) on a wet basis [ISO 10780].

step factor: The factor by which each dilution level in a dilution series differs from adjacent dilution levels.

sub-threshold: Pertaining to a stimulus below the specified threshold. [ASTM E253-97]

supra-threshold: Pertaining to a stimulus above the specified threshold. [ASTM E253-97]

test administrator: See "panel leader."

triangle test: A method of difference testing comprising three coded samples, two of which are the same. The assessor is asked to select the odd sample.

triangular forced choice: A method of olfactometry testing where the assessor is given two blank (odor free) presentations and one dilute odor sample. The assessor is forced to choose which of the three presentations contains the odor.

trueness: The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value [ISO 5725, part 1].

yes / no method: A method of olfactometry in which assessors are asked to judge whether an odor is detected of not at multiple dilution levels.

Z: The variable which stands for a dilution ratio.

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