®
D r o p C o u n t e r
P S - 2 1 1 7
3
Figure 3: Graph of pH versus volume
Tips
•
Except for opening and closing the stopcocks, do not touch
the syringe during the titration; otherwise, the drop size may
change significantly.
•
The drop rate must remain approximately constant (about 2
drops per second) in order for the drop size to remain con-
stant.
•
Drop size depends on the exact position of the bottom stop-
cock. Therefore, the average drop size will be different for
every titration. For each titration, re-enter the volume used
and drop count values in the calculation.
Other Titrations
Titrations with different solutions can be performed using the
same equipment and procedure. Other probes (such as conductiv-
ity or ORP) can be used in place of the pH probe.
Theory of Operation
The Drop Counter uses an
infrared light source and a
photodetector. Lenses
spread the light into a
“sheet” and refocus it
onto the photodetector.
When a drop of fluid
passes through the Drop
Counter, it partially
blocks this sheet of light, and the photodetector registers a
momentary decrease in light intensity.
The Drop Counter uses infrared light and ignores visible light.
On power up, it automatically adjusts the light level for the best
sensitivity. Use the Drop Counter away from direct sunlight or
other sources of infrared that may interfere with it.
When the Drop Counter detects a falling drop, the green indicator
light emitting diode (LED) flashes. If something stationary is
blocking the photodetector, the indicator LED remains on.
Troubleshooting
Specifications
Technical Support
For assistance with any PASCO product, contact PASCO at:
For more information about the Drop Counter and the latest revi-
sion of this Instruction Sheet, visit the PASCO web site and enter
PS-2117 in the Search window.
Limited Warranty
For a description of the product warranty, see the
PASCO catalog.
Copyright
The PASCO scientific 012-08470D
Drop
Counter Instruction Sheet
is copyrighted with all rights reserved. Permis-
sion is granted to non-profit educational institutions for reproduction of any
part of this manual, providing the reproductions are used only in their labo-
ratories and classrooms, and are not sold for profit. Reproduction under
Select volume calculation
for horizontal axis
detector
collimating
lens
focusing
lens
sheet of light
drop
infrared light
source
Figure 4: Diagram of Drop Counter
Problem
Cause
Solution
Indicator light flashes
twice for a single drop.
Drop Counter registers
more drops than
actually dispensed.
Fluid is splashing
back into the drop
window.
Adjust the position
of the beaker, Drop
Counter, or syringe
to eliminate splash
back
Indicator LED remains
on constantly. Drop
Counter does not
register drops.
Lenses in drop
window are dirty or
wet.
Clean lenses with
water and dry with a
cotton swab or
tissue.
Maximum drop rate
40 drops per second
Default sample rate
5 samples per second
Maximum sample rate
10 samples per second
Minimum object detection size
0.64 mm diameter
Enclosure
Polypropylene, water resistant,
chemically resistant to mild acids
and bases
Detector type
Infrared photodetector with
collimating lens
Address: PASCO scientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone:
+1 916 786 3800 (worldwide)
800-772-8700 (U.S.)
Web:
www.pasco.com
Email:
