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CASY TT Operator‘s Guide
2.1 Measuring Unit
The measuring unit (see Figure 5) contains the measuring electronics, the fluid system and the
valves required to control the measuring process. The close monitoring of the measuring volume
(200 or 400 µl) required to determine the concentration is carried out by a light-barrier monitored,
calibrated precision vertical tube. The CASY System handles larger measuring volumes (maximum
4 ml), employing a multiple measurement system. The results of the individual measurements are
accumulated. The CASY System operates almost dead-volume free, i.e., the required sample quan-
tity is only slightly larger than the measuring volume. The control and monitoring of the measuring
process are designed to exhibit maximum protection against interference. Any faults that do occur
are automatically detected by the CASY System and the user is notified.
The sampling chamber accommodates the following elements:
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Measuring capillary
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External electrode
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Sample platform
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Waste container (left)
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Storage container (right)
The measuring unit is controlled by the control panel (see Chapter 2.4 and Figure 6). An inspection
window, which also enables the vertical tube to be monitored visually, is situated above the sam-
pling chamber. The inspection window accommodates three light-emitting diodes, which indicate
the filling level of the vertical tube. The green light-emitting diode indicates the start of a measure-
ment, the lower red light-emitting diode indicates when the 200 µl level is reached and the upper
red light-emitting diode indicates when the 400 µl level has been reached.
Before the start of each measurement, the contents of the measuring capillary are emptied into
the waste container. The sample volume is then aspirated through the measuring capillary under
constant low pressure. The progress of the meniscus can be tracked in the inspection window. The
time required to reach the light barriers depends on the diameter of the used measuring capillary
and is precisely monitored by the CASY System. This process enables potential faults resulting from
measuring capillary blockages to be automatically detected. During the measurement process, the
vertical tube is also monitored for disturbances caused by air bubbles.
Blockages are removed by running a clean cycle, which, in addition to refilling the internal fluid sys-
tem, actively counter-flushes the measuring pore (see Chapter 6.4). The required CASY ton is sucked
in from the storage container and then emptied into the waste container. The entire volume of the
internal fluid system is approx. 2 ml.
Measuring Unit
