Lumiso Photometers – Checking the Calibration
What are Check Standards and why should you use them?
Check Standards are available for all Palintest photometers and are used to check the calibration of the instrument to ensure it is performing correctly.
Lumiso photometer check standards are Neutral Density Filters (NDFs). A Neutral Density Filter is an optical filter that absorbs light of all wavelengths to the same extent. Therefore, they are very predictable when used as check standards in optical instruments such as Lumiso photometers. The standards are made of a piece of coloured glass rather than a liquid. This means they are non-hazardous and are stable for longer than a liquid check standard.
How do the Lumiso Check Standards work?
The check standard procedure for our Lumiso photometers is simple and easy to carry out. Lumiso check standard kits consist of one blank and one to three standards depending on the instrument. Lumiso check standards will check the wavelengths of light that the instrument uses, rather than the concentration measurement for each individual parameter.
The blank standard is used first, followed by the other standard(s). For our handheld Lumiso photometers, the value shown on screen is then compared to the certificate provided in the check standard kit to confirm that the photometer is conforming to our calibration standards. For the Lumiso Expert and Lumiso Pooltest Expert, a code on the calibration certificate can be entered into the instrument to assign the values of the check standard set being used. Following this, the check standard procedure can be carried out and the instrument will calculate if the check standards pass or fail, which will indicate if the instrument is conforming to our calibration standards and therefore measuring within calibration.
The blank, and standard(s) must be tested at all wavelengths the instrument measures. The label on the top of the standard indicates how to align the standard depending on the wavelength being measured. Full instructions will be provided with your check standard kit.
Why do Lumiso Check Standards measure Percentage Transmission (%T) rather than concentration?
Lumiso works, like all photometers, by measuring the amount of light that passes through the sample. This value is known as the “Percentage Transmission” or “%T”.
Lumiso’s software will convert the %T value measured into a concentration of chemical, such as mg/L of chlorine. Therefore, to verify that the instrument is within calibration it is only necessary to check that the instrument is measuring %T correctly for each wavelength of light it uses. This simplifies the check standard testing procedure and is quicker than testing individual parameters.