Vernier

A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement uncertainty by using vernier acuity to reduce human estimation error. It may be found on many types of instrument measuring linear or angular quantities, but in particular on a vernier caliper, which measures internal and external diameters.

The vernier is a subsidiary scale replacing a single measured-value pointer, and has for instance ten divisions equal in distance to nine divisions on the main scale. The interpolated reading is obtained by observing which of the vernier scale graduations is coincident with a graduation on the main scale, which is easier to perceive than visual estimation between two points. Such an arrangement can go to a higher resolution by using a higher scale ratio, known as the vernier constant. A vernier may be used on circular or straight scales where a simple linear mechanism is adequate. Examples are calipers and micrometers to measure to fine tolerances, on sextants for navigation, on theodolites in surveying, and generally on scientific instruments.The Vernier principle of interpolation is also used for electronic displacement sensors such as absolute encoders to measure linear or rotational movement, as part of an electronic measuring system.

Vernier

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Vernier scales work so well because most people are especially good at detecting which of the lines is aligned and misaligned, and that ability gets better with practice, in fact far exceeding the optical capability of the eye. This ability to detect alignment is called vernier acuity.[5] Historically, none of the alternative technologies exploited this or any other hyperacuity, giving the vernier scale an advantage over its competitors.[6]

Zero error is defined as the condition where a measuring instrument registers a reading when there should not be any reading. In case of vernier calipers it occurs when a zero on main scale does not coincide with a zero on vernier scale. The zero error may be of two types: when the scale is towards numbers greater than zero, it is positive; otherwise it is negative. The method to use a vernier scale or caliper with zero error is to use the formula

Positive zero error refers to the case when the jaws of the vernier caliper are just closed and the reading is a positive reading away from the actual reading of 0.00 mm. If the reading is 0.10 mm, the zero error is referred to as +0.10 mm.

Retrograde verniers are found on some devices, including surveying instruments.[7] A retrograde vernier is similar to the direct vernier, except its graduations are at a slightly larger spacing than on the main scale. N graduations of the indicating scale cover N + 1 graduations of the data scale. The retrograde vernier also extends backwards along the data scale.

Hello again, hope you are doing great!

Seems to me that you are following the proper steps as per the manual says, is there a way you can post the Lab/code so I can take a look at it, however should be a staright forward process.

I cant think of a steps that need to be done before setting up the hardware or software, however you can verify that the DAQ assistant on the block diagram is configured properly meaning the NI ELVIS is selected and the proper channels are in fact the ones you have connected to the vernier instrument and the ELVIS board. Code-wise there is not much that can be interfering with our acquisition, as far as I know we use the DAQ assistant express VI where the only setup available is the Device and channel you will use.

Found in every machine shop, vernier calipers measure internal, external, depth, and step dimensions to an accuracy of 0.001" up to a 60" range. These calipers are traditional, yet continue to be widespread in many industries. They not only measure the straight distance between two points. They are also used for measuring the diameter of cylinders and holes.

These high quality, basic vernier calipers offer inch and metric measurement. They feature a lock screw for sliding jaw, and a hardened stainless steel depth rod. Graduations are .001" inch, 0.020mm metric.

Vernier calliper with a vernier scale on the sliding secondary scale. On the vernier scale the zero line provides the reading before the decimal point (12 mm), while the non-zero line (3) that aligns most closely with a line on the major scale provides the reading after the decimal place. This totals a measurement of 12.3 mm.

The vernier threshold (smallest detectable offset) for humans is as low as 2 to 5 arcseconds (Westheimer and McKee, 1977b; Westheimer, 1987). Vernier acuity is hence regarded as a type of hyperacuity (Westheimer, 1975), a term that describes visual tasks that have thresholds smaller than the size of a foveal cone (2.5 m, about 30 s of arc), which limits the classical spatial resolution of the eye. Other examples include stereoscopic acuity (binocular vision), line orientation discrimination, and detection of curvature (Westheimer, 1981).

(A) Vernier stimuli can consist of pairs of discrete dot-like shapes, lines or other juxtaposed elements where an offset occurs in a direction perpendicular to a line joining the features of interest. (B) When measuring vernier acuity with steady state visual evoked potentials, animations that transition between aligned and misaligned stimuli are used. (C) Preferential hyperacuity perimetry requires the subject to identify misaligned dots on a computer screen.

Several key open source computer software programs for the psychophysical measurement of vernier acuity are available online. The vernier acuity module of the Freiburg Acuity Test (FrACT) software1 includes an automatic 2AFC staircase with the BestPEST adaptive algorithm on the direction (left or right) of horizontal offset between the position of two vertical lines. The FrACT has been well validated and established in the measurement of acuity in low vision patients (Lange et al., 2009; Jolly et al., 2019). The vernier acuity module provides a valuable adjunct in the battery available. The Psychophysics Toolbox2 can be run on Matlab or Octave to display vernier targets and measure vernier thresholds; Psychopy3 is a Python-based package that offers similar functions.

A comparison between the concepts of visual acuity and vernier acuity using a hexagonal mosaic model of retinal photoreceptors. Yellow circles with blurred edges represent areas of retinal illumination. Classical visual acuity, or resolution acuity (R), involves resolving two stimuli as separate and requires a gap in retinal illuminance to be detected by a photoreceptor located between other photoreceptors receiving stimulation. Vernier acuity (V) involves localisation of the difference in spatial positions of two separate stimuli.

The development of more sensitive experimental techniques, particularly for retinal image stabilisation, has provided further support for the importance of small eye movements in both hyperacuity and conventional visual acuity (Strasburger et al., 2018). Averill and Weymouth (1925) measured a two-fold reduction in vernier thresholds when stimulus exposure time was reduced from 1540 to 30 ms, a time frame chosen to restrict eye movement response, though they were only able to partially control for differences in light flux with their technology at the time. More sensitive methods by Westheimer and McKee (1977a) with full equating of light flux across the exposure period found vernier thresholds relatively unchanged with exposure times as low as 11 ms, suggesting that eye movements are not an absolute limiting factor for vernier acuity (Westheimer, 2018).

Psychophysical methods, electroencephalography (EEG) and cortical imaging have assisted to elucidate the nature of the cortical mechanisms underlying vernier acuity. Both the primary visual cortex (V1) and extrastriate cortical regions have been implicated in the cortical processing of vernier stimuli. Hou et al. (2017) carried out source imaging studies using functional magnetic resonance imaging (MRI)-informed EEGs to localise sources of vernier and grating acuity in four visual regions: V1, lateral occipital cortex, hV4, and middle temporal cortex. V1 and lateral occipital cortex were the most sensitive cortical areas to vernier displacement stimuli, providing further evidence that detection of vernier acuity involves striate mechanisms. However, grating stimuli (which reflects resolution limits) evoked equal responses in all four regions. Later studies measuring vernier-related activity with steady state VEPs showed a predominant initial response over medial occipital electrodes, with broadly distributed secondary responses occurring later that were consistent with a feedforward pathway originating in the early visual cortex and progressing to higher-order areas (Barzegaran and Norcia, 2020). In contrast, VEPs for letter acuity showed a dominant component over the lateral occipital areas, particularly in the left hemisphere, with later responses at the early visual areas due to feedback. The differences in cortical response topography indicate that while the cortical sources of vernier and letter acuity are distinct, they both undergo processing in the early visual cortex.

Vernier acuity is resistant to contrast and luminance changes at suprathreshold levels (Wehrhahn and Westheimer, 1990; Waugh and Levi, 1993b), with detection reaching its optimum level at a Michelson contrast of 0.22 when background luminance is 860 cd/m2. An exponential increase in the vernier threshold at contrast below 0.22 was found. In terms of decimal acuity, vernier acuity is 10-fold that of visual acuity both under photopic and scotopic conditions (Freundlieb et al., 2020). Most studies in the literature test at a Weber contrast of 90% or above, or a Michelson contrast of 80% or above. Studies investigating the relationship between target contrast and target separation using vernier line targets suggest that vernier acuity demonstrates contrast-dependent mechanisms when there is a small separation (2 arcminutes or below) between the targets, whereas larger separations (4 arcminutes or above) are contrast-independent (Waugh and Levi, 1993a). This led to the hypothesis that spatial filters that depend on contrast are involved in the processing of close targets, but not of targets with large separation. e24fc04721