PASCO CI-6499 User Manual

Instruction Sheet
for the PASCO
Model CI-6499

012-08549A

Drop Counter

Label with light-emitting
(LED) indicators

1/2” Probe Holders

1/4” Probe
Holder

Drop

Set screws

detection opening

Introduction

The PASCO CI-6499 Drop Counter counts drops/
sample and displays the drop count (drops) and fluid
volume (mL) of liquids and fine particles.

When the Drop Counter is used with a
ScienceWorkshop® interface and DataStudio software,
drop count and fluid volume can be viewed in
real-time in a graph display.

Typical applications for the Drop Counter include
measuring drop count and fluid volume, titration
experiments, and particle counts.

Equipment Included:

• CI-6499 Drop Counter

• Syringe Assembly with two stopcocks

• Plastic tips for buret (1 small, 1 medium)

Stainless steel rod

5’6” cable

Stereo plug

Plastic syringe

Additional Equipment Required:

• ScienceWorkshop® interface (500 or 750)

• DataStudio® software (version 1.8.5 or later)

Specifications:

Sensor range: 0 to 40 drops/second
Default sample rate: 5 samples/second
Maximum sample rate: 10 samples/second
Object detection size: 0.64 mm diameter (liquid drop
or fine particle)
Plastic enclosure: polypropylene, water resistant,
chemically resistant to mild acids and bases
Detector: Infrared photodetector with collimating lens

Probe holders: 2 x 1/2”, 1 x 1/4”

stopcocks

plastic tip

© 2003 PASCO scientific

Drop Counter 012-08549A

Drop Counter Detector Operation

The Drop Counter includes a photodetector, which
records the change in infrared light emitting from the
aperture. As the drop falls between the lenses, it
penetrates a thin sheet of light. Light emitted from the
infrared light source enters the aperture, travels
through a collimating lens, and exits another aperture
before reaching the photodetector. In Figure 1, the
arrows indicate the direction of light travel.

infrared light source

drop

collimating
lens

sheet of light

Figure 1: Detector Operation

When the detector recognizes a drop, the green light
flashes. The light remains on when something is
blocking its path. The Drop Counter blocks all
visible light and works off of infrared light. On
power up, the detector automatically adjusts the light
level for the best sensitivity.

detector

focusing lens

thumbscrews for mounting up to three sensor probes. Typical
sensors used are the pH Sensor (CI-6507A) and the
Temperature Sensor (CI-6505B). A Teflon

®

sleeve is

recommended for use with these probes (part no. 669-075).

Drop Rate and Drop Size

For best results, use the included syringe with the Drop Counter.
The syringe has two stopcocks. Use the top stopcock to select a
flow rate during calibration and adjust the rate during the run.
Use the bottom stopcock to start and stop the liquid flow. The
tip provided with the Drop Counter helps to ensure a consistent
drop size. The drops from a glass tip are commonly twice the
size of drops from plastic tips, and the volume per drop for a
glass tip is not as consistent.

Shaking the syringe during the titration can affect the drop size
and the flow rate by causing small drops to fall. Avoid making
unnecessary adjustments during the run. Exceptions include the
following: the system needs to be refilled or the drop rate falls
below 1 drop/second. If the drop rate is below 1 drop per
second, the drop size increases (up to 2 - 3 times larger) and this
causes inaccurate volumes. If the flow rate falls below 1 drop
per second, and a large volume of liquid remains in the syringe,
adjust the stopcock to increase the flow. If the liquid level is
low, turn off the stopcock and refill the syringe before turning it
on at the higher drop rate.

Sensor Usage Tips

• Avoid operating the Drop Counter in direct sunlight.

• The green LED will flash once per drop. Two flashes
per drop indicates that a splash caused a count. If the
LED stays lit, then the lenses need to be cleaned.

• If the lenses become dirty or wet, clean or dry with

a cotton swab or tissue. The lenses are located in the

slits in the rectangular opening. WARNING: Do not

use chemicals to clean the lenses. Abrasive

chemicals may damage the lenses!

• To avoid miscount errors from splashing and/or
potential lens damage, use a magnetic stirrer.

• The Drop Counter has two different size holes with

It can take several seconds for each drop to mix, but the pH
probe detects more concentrated fractions as often as less
concentrated fractions. Therefore, the mixing tends to occur
without systematic error.

CAUTION: If you use a buret, slowly turn the stopcock to
allow drops of liquid to drip and avoid streams of liquid bursting
from the valve early on in the count. Bursts of liquid will distort
the actual count or volume dispensed.

The common 25 or 50 mL buret is long enough that the pressure
variation from the bottom to the top of the buret will change the
flow rate. With some burets, the rate can drop below 1 drop per
second, which may cause drops to become larger and
unpredictable. If using a glass buret, start at a rate of 3 to 4
drops/second. When the rate slows, stop, take a volume reading,
refill the buret, and start again at the faster rate.

2