The Enviroscopics Visual Clarity Wedge (EVCW) or Secchi Wedge is an inexpensive supplement to the electronic turbidimeter and can be used for estimating and tracking changes in turbidity levels.

This tool is the improved evolutionary descendant of the Triton Turbidity Wedge, which was developed by the same designer for water quality monitoring on the Vancouver Island Highway Project and has been in use by environmental professionals in the private and public sectors for the past 8 Years.

Improvements include:

1) Continuous rather than incremental scale.

2) Sliding cursor with "Secchi Disc" type target pattern produces more objectivity in the determination of values.

3) Direct measurement in cm and direct approximations of Nephelometric Turbidity Units (NTU).

4) Tougher construction (1/4" Acrylic body)

The Design

Like its pre-cursor, the EVCW is used to measure the distance to extinction of an image by horizontal viewing through a fluid contained within the vessel. The vertically tapered body with opposing viewing window and target plate allows for a range of viewing distanced from 0 to 20 cm. This provides for an approximation of turbidity values from about 50 NTU and up.

Unlike the former unit, in which the target plate was also the reading scale, this unit uses a moving "Secchi Disc" type target design, which requires the measurement to be set prior to being read which must be done by looking at the reverse side of the instrument.

The moving target, while being designed after a well established pattern in use for many years in the Secchi Disc, provides a much more effective visual cue than a static pattern as our visual sense is stimulated by movement. When moving the target back and forth through the medium, we can either see the movement or not. In contrast, looking at a static, repeating pattern, fading gradually out of sight, can be confusing, as our brain is very good at filling in missing information for us.

Benefits

1) The wedge, being a manual tool contains no batteries or sensitive electronics, prone to break down under rugged field conditions.

2) It can be used as a routine measuring tool or as a back-up to electronic instruments.

3) As well as providing a measurement of turbidity, the tool provides an opportunity for observation of other characteristics of the sample material such as the types of suspended and floating or settling material, colour etc.

4) Hands on contact can help to eliminate a tendency common to electronics of providing unfounded numbers that may be the result of instrument malfunction or reading error.

5) Cost is less than 1/10 that of an electronic instrument

$250 Canadian

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