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Introduction
1.2 Measuring Principle
The technology of CASY Systems combines a proven particle measurement technique, referred to
as the
“Electrical Sensing Zone” technique (ISO 13319), with a modern method of signal evaluation, the
“Pulse Area Analysis”.
1.2.1 Digital Pulse Processing
Pulse Area Analysis was developed in 1987 on the basis of Digital Pulse Processing (DPP), a tech-
nique developed for the digital recording of electrical signals more than 40 years ago. For cell
analysis, DPP is combined with a high scanning rate and a highly-standardized method of analyzing
cell signals. This combination facilitates unprecedented measuring range dynamics and guarantees
maximum resolution and excellent reproducibility for all measuring parameters.
Lift tube
Start
400 µl
200 µl
Measuring
pore
Electrodes
Measuring
capillary
Electrolyte solution (CASY ton)
with cells in suspension
Figure 1: Measurement principle of the CASY Cell Counter and Analyzer.
As shown in
Figure 1
, cells are suspended in CASY ton, an electrolyte developed specifically for cell
counting. For the measurement, the cells are aspirated through a precision measuring pore of de-
fined geometry at a constant flow speed.
Signal Generation
The precision measuring pore is designed as a hole within an artificial precious stone, which is
cast inside the capillary body. The electrolyte-filled measuring pore represents a defined electrical
resistance (constant current). During their passage through the measuring pore, the cells displace
electrolyte and thereby generate electrical pulses. Each generated electrical pulse is recorded as a
cell count and the size of each pulse is equivalent to the cell volume because every cell displaces
exactly the quantity of electrolyte corresponding to its cell volume. The changes in voltage when a
cell or particle is passing the pore are sampled with a frequency of 1 MHz.
Measuring Volume
For calculation of the cell concentration it is essential to know the exact volume of the cell suspension
passing the measuring pore. This volume (measuring volume) can be defined by the user and is pre-
cisely determined by the CASY System using a lift tube, which is calibrated in volume.
Measuring Principle
Digital Pulse Processing
