Advanced Instruments 4250, Руководство пользователя

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Advanced
®
Cryoscope Model 4250 User’s Guide
arbitrarily-selected freezing point value can be useful in quantifying rel-
ative deviation. For example, having determined the average local freez-
ing point and normal variation of the milk of a particular cow, herd or
breed, one can estimate the percentage of deviation due to a particular
condition, disease or additive.
The option to set a base freezing point value and have the cryoscope
calculate the percent deviation from the base, of each sample tested, has
been built into the Model 4250. However, since it is no longer accept-
able (nor accurate) to label all positive deviations from a base value as
“ added water, ” we suggest reporting deviations from a base as “ % DFB ”
(percent deviation from base). Using % DFB in this manner can provide
a guideline for estimating the quality of milk samples in respect to the
base established. All unknown samples of milk run against this base
value will show a deviation above or below the base.
The 4250 calculates the percent deviation from the base (% DFB) as
follows:
DFB = (base value - observed value)/base value x 100
As noted, part of this deviation is attributable to natural variation and
measurement error. Factors other than the addition of water to milk,
which can cause additional positive deviations from the base (DFB),
include:
1. Poor herd condition
2. Poor feed and/or pasture conditions
3. Drought conditions
4. Extended milk storage, CO
2
decrease
Factors which can cause unacceptably negative deviations from the base
(% DFB) include:
1. Dirty sample tubes
2. Sour milk
3. Chlorine sanitizer in the milk sample
4. Milk adulterated by salt-fortified water