FAQ: "We have a customer complaint about APHA readings in EasyMatch QC. As soon as APHA is selected as an index in EZMQC the instruments (CQXEs) flash three times before showing the result. Instruments flash once only for all other transmission readings when APHA is disabled. Customer is more than happy with single flash accuracy and repeatability, measurement speed is highest priority. How can we change this?"
APHA is a very sensitive metric for quantifying trace amounts of yellowness in near water-white liquids, a high performance application.
Whenever APHA is selected as a metric, all HunterLab sphere instruments flash 3 times and average the results to report a single APHA reading. This implementation has been in place for years and works very well in the field as your customer has noted.
The reason for this implementation was in response to previous customer and sales requests. In our software APHA displays to 2 decimals places when it should correctly display to only 1 given the sensitivity of the metric. Unfortunately, it was implemented to 2 decimal places in our previous Universal software, and when an attempt was made to change this back to 1, our sales team made the case that customer were familiar with the display of APHA to 2 decimal places and our instruments were very repeatable and capable of this level of precision.
Other customers and sales representatives noted that APHA measurements varied slightly in the second decimal place (intended for round-off only), particularly in instruments that had been out in the field for several years.
Our solution was to average 3 readings whenever APHA is selected for display. Typical lamp life on our sphere instruments extends to well over a million flashes. Averaging 3 flashes per APHA reading is not considered significant in terms of the perceived performance in APHA/Pt-Co measurement.