Model OUM980 with OUSAF21 Inline Sensor
General Information
7
2.
General Information
The Model OUM980 Photometric Analyzer is used in conjunction with a Model OUSAF21 sensor to measure the spectral
absorbance of process liquid in the VIS/NIR region of the electromagnetic spectrum.
Dependent upon the optical pathlength of the connected sensor, the instrument can measure up to 50 Optical Density (OD) units.
The Model OUM980 Photometric Analyzer is manufactured from state of the art digital electronics. Plant interface is through quick
disconnect screw terminals on the back of the module. The user interface is comprised of a 6-button tactile feel keypad and 4 x 20
character alphanumeric LCD display.
2.1
How the Model 980 Photometric Analyzer Works
The Model OUSAF21 sensor generates two photocurrent (nA) detector signals based upon the amount of energy present at its lamp
source (reference) and measurement point internally. The Model OUM980 unit computes the logarithmic ratio of these two signals
and determines the absorbance of the liquid passing through the sensor. The absorbance value is expressed in optical density units
(OD) and is displayed on the front panel. Two galvanic isolated analog current outputs, proportional to the OD reading, are
simultaneously transmitted for connection to other instrumentation and recording devices.
2.2
Concentration and Absorbance Units
The concentration of an optically absorbing material in a mixture can be determined since it is related to the amount of light
absorbed from a beam of light passing through it. The absorbance of a substance is directly proportional to the concentration of the
material that causes the absorption. The Lambert-Beer Law describes this relationship of absorbance (A) to concentration.
Essentially, the amount of radiation transmitted through the absorbing material decreases logarithmically with its increasing
concentration.
Where
Ir
Io
T
A
log
1
log
and
Io
Ir
T
The above assumes that the optical pathlength remains constant. The optical density (OD) however, is defined as Absorption per
unit length. Normalizing to an optical pathlength of 1cm, it follows that:
)
(
1
A
L
OD
Where
OD = Optical Density
A = Absorbance
L = pathlength in cm
2.3
Easy Interfacing
The Model OUM980 Photometric Analyzer incorporates a front panel display and two analog current output signals. The display on
the front panel is an alphanumeric 4 x 20 character LCD. The display may be configured for process variable or analog current
output measurements. Optical Density (OD) readings are normalized to a 1cm pathlength.
