YSI 55 - Manual (Page 9)

5
4. Preparing The Probe
4.1. Description
The YSI Model 55 dissolved oxygen probe is a non-
detachable, polarographic sensor designed
specifically for the YSI Model 55 Handheld
Dissolved Oxygen System. Probe cables are
available in lengths of 12, 25 or 50 feet.
4.2. Choosing The Right Membrane
The YSI Model 5775 Standard Membrane Kit is
supplied with the YSI Model 55. This kit contains
thirty 1 mil (.001") membranes and a bottle of KCl
solution. YSI recommends the 5775 membranes for
most applications.
For special conditions, a 0.5 mil (.0005") membrane
is available. Order YSI Model 5776 High
Sensitivity Membrane Kit. This half-thickness
membrane improves measurement time at low temperatures and helps suppress background current
at very low dissolved oxygen levels. When data is routinely collected at sample temperatures below
15
o C and at dissolved oxygen levels below 20% air saturation, the low signal current resulting from
the use of the standard membranes tends to magnify the probe's inherent constant background signal.
Using the high sensitivity membranes in this situation will decrease the percentage of error due to
the probe's background current.
For long-term monitoring situations ONLY, a half-sensitivity, double-thickness, 2 mil (.002")
membrane is available. For these applications, order the YSI Model 5685 Membrane Kit, which
includes membranes and electrolyte.
4.3. Probe Preparation
The YSI Model 55 probe is shipped dry. Before using the Model 55, the protective membrane on
the probe tip must be removed, the probe must be filled with KCl solution and a new
membrane must be installed. Follow the instructions below to install the KCl solution and
membrane.
To prepare for installation of a new membrane on your YSI Model 55 dissolved oxygen probe:
1. Unscrew the probe sensor guard.
2. Remove the old O-ring and membrane.
3. Thoroughly rinse the sensor tip and KCl reservoir with distilled water.
4. Prepare the electrolyte according to the directions on the KCl solution bottle.