Precision Measurement Engineering, Inc.
Precision Measurement Engineering, Inc.
The PAR (Photosynthetically Active Radiation) responds to ambient light in the photosynthetically active band. The sensor is essentially a photo diode that receives light through a bandpass optical filter. The sensor produces an electrical current that is directly proportional to the flux of photons into the photo diode. This current is amplified by circuits on SCAMP's 5550 fluorometer circuit assembly, low pass filtered, and digitized by SCAMP's A/D.
The sensor is a Li-Cor LT-192SA. For more information about this sensor see the LT-192SA manual.
The PAR sensor is directional. Presently it can be mounted so that it looks away from SCAMP from the weight release end as shown in the picture below. When connected this way it is sensitive to downwelling light when SCAMP profiles in downwards mode and to upwelling light for SCAMP's upwards mode profiling. It is possible to place the sensor on the other side of the drag plate to get downwelling light in upwards mode. This requires modifications. Contact PME for more information. The picture also shows two white floats that must be added to compensate the system for the extra weight of the PAR sensor.
The PAR sensor is connected to circuits inside SCAMP by using a special I/O cable assembly, and a special 4 pin I/O connector. The I/O cable assembly connects to the SCAMP I/O connector, then 'Ys' to connect to the PAR sensor and also to provide the usual I/O connection for uploading SCAMP.
USB SCAMP has a slightly different I/O connector mounted on the SCAMP release end cap. This connector has proven quite susceptable to damage due to bending the attached cable near the connector. PME provides a cable protector as shown in the previous picture. The protector is a white cylinder that slips over the connector and cable. The end with the small transverse hole goes against SCAMP's end cap. The cylinder is secured into position by threading a small cable tie throught the transverse hole in such manner that it does not interfere with the release motor or weight cable. The pencil in the above picture points to the protector and cable tie.
PME does not calibrate the PAR sensor. Instead PME takes the
calibration provided by LI-COR and implements it taking into account how the SCAMP
electronics responds to sensor current.
PAR sensors are usually ordered when SCAMP's fluorometer is installed. SCAMPs can be
retrofitted to add PAR at any time.