YSI 52 - Manual (Page 5)

SECTION 1 INTRODUCTION
The YSI Model 52 is a microprocessor-based instrument designed for field and
laboratory measurement of dissolved oxygen. Readings are automatically compensated
for temperature. When calibrated to percent air saturation, the display simultaneously
shows dissolved oxygen in mg/L and in percent air saturation as well as temperature in
degrees Celsius.
An RS232 port permits results to be sent directly to your serial printer or personal
computer. Salinity compensation can be adjusted manually. To assure the highest
accuracy, an auto stable feature indicates when the readings have reached user-defined
criteria for stability. To assure correct operation, the meter performs a self-testing routine
each time it is turned on; any error is then signaled on the display.
Calibration is quick and easy. Procedures for calibrating with and without compensation
for temperature, altitude, pressure, and salinity are described in this manual. The YSI
Model 52 is also equipped with non-volatile memory, capable of storing up to 70 DO and
temperature readings. Any data stored in internal memory can be reviewed on the LCD,
or batch uploaded to a PC or an RS232 printer.
Power can be provided by an AC adapter (optional), or batteries that permit field use.
1.1 PRINCIPLES OF OPERATION
YSI dissolved oxygen probes use membrane covered, Clark-type polarographic sensors
with built-in thermistors for temperature measurement and compensation. A thin semi
permeable membrane, stretched over the sensor, isolates the sensor elements from the
environment, but allows oxygen and certain other gases to enter. When a polarizing
voltage is applied across the sensor, oxygen that has passed through the membrane reacts
at the cathode, causing a current to flow.
Oxygen diffuses through the membrane at a rate proportional to the pressure difference
across it. Since oxygen is rapidly consumed at the cathode, it can be assumed that the
oxygen pressure inside the membrane is zero. Hence, the amount of oxygen diffusing
through the membrane is proportional to the absolute pressure of oxygen outside the
membrane. If the oxygen pressure increases, more oxygen diffuses through the
membrane and more current flows through the sensor. A lower pressure results in less
current.
YSI, Incorporated Model 52 1