Method for calibrating a particle counting apparatus
A method of calibration of a particle characterization apparatus, and a particle characterization apparatus, in which particles suspended in a liquid are passed through an orifice one by one for characterization of the particles, for instance by Coulter counting. The calibration does not require utilization of special calibration particles or liquids. A priori knowledge of the shape of a typical size distribution of a blood sample is utilized to adjust the apparatus based on an initial relatively short counting period of the sample in question. The initially determined size distribution is compared to the corresponding known typical size distribution and the apparatus is subsequently adjusted to counteract possible differences. Upon adjustment of the apparatus, the remaining part of the sample is passed through the orifice for determination of the actual particle size distribution of the remaining sample.
1. An impedance particle counter for determining a particle size distribution in a sample containing the particles by determination of the corresponding pulse height distribution, the impedance particle counter having a controller that is programmed for
a) controlling the impedance particle counter to count particles contained in a first part of the sample to determine the number of particles in each bin of a predetermined set of bins having different bin limits,
b) adjusting bin upper and lower limits in accordance with the determined number of particles in each bin and based on a priori knowledge of a typical particle size distribution of the type of sample in question, and
c) counting particles contained in a second part of the sample based on the adjusted bin upper and lower limits to determine the number of particles in each bin,
wherein at least one of the bin limits are adjusted according to the formula:
UpperLimit
(
B
i
)
=
C
1
a
0
·
W
0
+
a
1
·
W
1
+
…
+
a
i
·
W
i
b
0
·
W
0
+
b
1
·
W
1
+
…
+
b
i
·
W
i
+
C
2
wherein C 1 and C 2 are constants, Bi is the i′th predetermined bin and Wi is the number of particle counts in the i′th bin, and UpperLimit(Bi) is the adjusted upper limit of the i′th bin.
2. An impedance particle counter for determining a particle size distribution in a sample containing the particles by determination of the corresponding pulse height distribution, the impedance particle counter having a controller that is programmed for
a) controlling the impedance particle counter to count particles contained in a first part of the sample to determine the number of particles in each bin of a predetermined set of bins having different bin limits,
b) adjusting bin upper and lower limits in accordance with the determined number of particles in each bin and based on a priori knowledge of a typical particle size distribution of the type of sample in question, and
c) counting particles contained in a second part of the sample based on the adjusted bin upper and lower limits to determine the number of particles in each bin,
wherein at least one of the bin endpoints are adjusted according to the formula:
UpperLimit
(
B
i
)
=
C
1
W
i
-
1
W
i
-
2
+
W
i
-
1
+
W
i
+
W
i
+
1
+
C
2
wherein C 1 and C 2 are constants, Bi is the i′th predetermined bin and Wi is the number of particle counts in the i′th bin, and UpperLimit(Bi) is the adjusted upper limit of the i′th bin.