Terrestrial Quantum Sensors Measure PAR LI-190 Quantum Sensor LI-191 Line Quantum Sensor	Underwater Quantum Sensors Measure PAR LI-192 Underwater Quantum Sensor LI-193 Spherical Underwater Quantum Sensor	Pyranometer Measure total solar radiation LI-200 Pyranometer	Photometric Sensors Light as seen by the human eye LI-210 Photometric Sensor

Cable Termination

There are several options available for cable lead termination on LI-COR radiation sensors. The two letters at the end of the model number denote the type of termination (e.g. “SA”). The following table describes these options:

Type	Termination	Description
SA	enlarge	Sensor lead terminates with a BNC connector for use with a LI-COR light meter or data logger. Sensor delivers a microamp current output. Type SA sensors can be used with non-LI-COR devices requiring a millivolt signal, with the use of the appropriate Millivolt Adapter. This adapter mates with the sensor’s BNC connector and terminates in bare wire leads. The resulting output is in millivolts, and is proportional to the sensitivity of the sensor to which it is connected.
SZ	enlarge	Sensor lead terminates with bare wires for use with a non-LI-COR metering device/data logger, or with the 1400-301 Terminal Strip, when used with the LI-1400 DataLogger. Sensor delivers a microamp current output. If required, a shunt resistor can be used across the terminals of the metering device to generate a millivolt output.
SL	enlarge	The sensor is coupled with a unique millivolt adapter containing a variable resistor. Output is standardized to 10 mV at full scale. Ultimate termination is bare leads. Designed for use with non-LI-COR devices that require a millivolt signal.

Milivolt Adapters

Millivolt adapters are used only for connecting sensors to a user’s datalogger or stripchart recorder, not the LI-1400 or other LI-COR readout devices.

The millivolt adapter connects to the BNC connector of the sensor, and the wire leads of the adapter are connected to the data logger. Sensor output (in millivolts) when using the millivolt adapter can be computed using "Ohm's Law" (Voltage = Current X Resistance).

Example: Calculate the millivolt output of an LI-190 Quantum Sensor which has a calibration constant of 8.0 µA/1000 µmol s^-1 m^-2. Assume the 2290 millivolt adapter is used with the sensor.

Type "SL" sensors are available for the LI-190, LI-191, LI-200, and LI-210 Sensors. The Type SL Sensor produces a standardized millivolt output, and may be used in place of the Type SA Sensor and Millivolt Adapter.

2290 Millivolt Adapter
For LI-190SA Quantum Sensor, LI-191SA Line Quantum Sensor, or LI-210SA Photometric Sensor (604 Ohm resistance).

2220 Millivolt Adapter
For LI-200SA Pyranometer Sensor (147 Ohm resistance).

2291 Millivolt Adapter
For LI-192SA Underwater Quantum Sensor or LI-193SA Spherical Quantum

Sensor (1210 Ohm resistance).

Table 1. Millivolt adapters for type "SA" sensors
Sensor	Millivolt Adapter	Resistance
LI-190SA	2290	604 Ohm
LI-191SA	2290	604 Ohm
LI-192SA	2291	1210 Ohm
LI-193SA	2291	1210 Ohm
LI-200SA	2220	147 Ohm
LI-210SA	2290	604 Ohm

Calibration of LI-COR Radiation Sensors

Recalibration of LI-COR radiation sensors is recommended every two years. Sensors must be returned to LI-COR for recalibration. Please contact LI-COR for a return materials authorization (RMA) number prior to returning any instruments.

Importance of Calibration
Calibration is an integral step in the manufacture or repair of all LI-COR optical radiation measuring instruments. All sensors are designed to provide data in standardized and accepted measurement units. Because of the normal variation in internal optical components, it is necessary to characterize each device by measuring its output from a standardized source. For fixed sensors, this calibration data is supplied as a "calibration constant" which indicates the amount of sensor output for a given amount of measurable energy.

There are two methods by which the readout device used with a sensor may be adjusted to the calibration constant to provide a direct readout. The constant is numerically entered into the instrument's internal electronic memory via the instrument's keypad. Adjustment of the internal "trimpots" (electromechanical memory) is done. Instruments without any provision for adjustment must have their data scaled by a factor determined from the calibration constant.

The characteristics of the optical components change with time and may also be affected by environmental conditions. Periodic recalibration is necessary to restore correct measurements. The time intervals suggested by LI-COR for recalibrations should be seriously considered. Data of a critical nature requires more frequent calibrations than those suggested, as well as calibrating under the conditions of actual use (e.g. same temperature). Ultimately, the only way to verify performance is to recalibrate.

Basis of Calibration
All LI-COR sensors (except pyranometers) are calibrated using working standard quartz halogen lamps, which have been calibrated against reference standard lamps traceable to the U.S. National Institute of Standards and Technology (NIST). Standard lamp current is metered to 0.035% accuracy. Microscope and laser alignment in the calibration setup reduce alignment errors to less than 0.1%. Stray light is reduced to less than 0.1% by black velvet background. The absolute calibration accuracy is limited to the uncertainty of the NIST-traceable standard lamp. The absolute calibration specification for LI-COR sensors is ± 5% (typically ± 3%) traceable to NIST.

Pyranometer sensors are calibrated against an Eppley Precision Spectral Pyranometer (PSP) under natural daylight conditions. Typical error under these conditions is ±5%.

Calconstants

Relationship between the Calibration Constant and the Calibration Multiplier
All LI-COR radiation sensors produce a current proportional to the radiation intensity. During factory calibration, sensor output (in microamps) is measured while the sensor is exposed to a standard lamp of known intensity. The sensor output at this intensity has general units of microamps per radiation unit and is called the Calibration Constant (Calconstant). Each sensor has a slightly different output at a given radiation intensity and will therefore have a unique Calconstant.

LI-COR Light Meters and dataloggers measure the current output of the sensor in units of microamps, and convert the measured current to units of radiation. To make this conversion, LI-COR instruments use the sensor Calibration Multiplier. The Calibration Multiplier is the negative reciprocal of the Calconstant.

Multiplier = -1/Calconstant

The Calibration Multiplier is always a negative number (because the shield of the coaxial cable of the sensor is positive instead of negative), and is expressed in radiation units per microamp.

For complete information on configuring your instrument, please consult your instruction manual or contact LI-COR. If the calibration constant for your sensor has been lost or misplaced, it can be obtained from LI-COR by providing the serial number of the sensor.