Page 103 - The Veterinary Laboratory and Field Manual 3rd Edition

72 Willy Schauwers

Per control weight a form for daily EQUIP-01–01 Daily control balance’. Indicate
weight control is available (see ‘FORM-SOP- for each balance which control weight should be
LABORATORY-EQUIP-01–01-Daily control used (see ‘FORM-SOP-LABORATORY-EQUIP-
balance’). 01–04-Balances and control weights’). Keep all
On this form, the following control weight information in the logbook.
specifications are mentioned: If the accepted limit values are exceeded, take
the following steps.
• mass of the control weight and mass mini-
mum/maximum limits, as listed by the • Check if the balance is completely level and
manufacturer if all weight measurements are properly per-
• make and type. formed.
• If there is still a problem, perform an internal
cErtIFIEd controL WEIGHt calibration of the balance (not all balances do
The certified control weights should be checked have this feature).
on a 3-yearly basis by a certified laboratory (a • If still a problem, contact the supervisor and
certificate should be provided). The certified check the balance with a certified control
control weights are usually kept by the quality weight.
management department or by the head of the • If still a problem, contact the manufacturer.
laboratory. • If the limit values are still exceeded, the possible
consequences on earlier weight measurements
HoW to PErForM tHE quaLIty aSSurancE should be considered. All measurements after
There should be quality assurance at three lev- the last successful control weight measure-
els: ment and before the exceeded measurement
should be traced. Possible consequences on
• daily control by the laboratory personnel by those laboratory results should be examined
measuring the control weights and rectified.
• half yearly control by the laboratory person- • The investigation of the problem and all
nel by measuring the control weight and the corrective actions are registered on ‘FORM-
certified control weight of every balance SOP-LABORATORY-EQUIP-01–02-Corrective
• if possible, a yearly servicing by the manufac- actions’.
turer of the balance.
HaLF yEarLy controL
daILy controL The balance is controlled half yearly by measur-
Every day (when the balance is used), before ing the control weight as well as the certified
the first use in the morning, the control weight control weight. Both weights are measured five
should be measured and recorded on the daily times. The average difference between both
control sheet. Do not touch the control weight weights has to be within a certain limit (see
with bare hands, always use gloves or forceps ‘FORM-SOP-LABORATORY-EQUIP-01–05-
to handle it. Per balance and per control weight Half yearly control of control weights’). This
accepted weight limit values are set (accord- limit value is determined by each laboratory
ing to the manufacturer of the control weight depending on the use of the balance. Balances
or on the basis of weight results gathered over used for preparing standard solutions have to
a long period and the standard deviation on be more accurate than balances used for weigh-
these results), see ‘FORM-SOP-LABORATORY- ing powders for bacteriology media preparation.

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