17
Calibration for Reflectance Measurements
After the Spectrophotometer has been switched on, zero calibration and white calibration must
be performed before spectral reflectance measurements are taken. Zero calibration is performed
using the Zero Calibration Box (which has a reflectance of 0%) to set the zero reference point for
reflectance measurements; white calibration is performed using a white calibration plate (which
has a reflectance of approximately 100% and for which spectral reflectance data are provided as
white calibration data) to set a high-reflectance reference point for reflectance measurements.
White calibration data
The white calibration data of the White Calibration Plate are provided under the following six kinds of
measurement conditions. When the CM-3700A is purchased, these data are already set within the instrument.
• Measurement area : SAV (3 x 5 mm) / Specular component : SCI
• Measurement area : MAV (ø 8 mm)
/ Specular component : SCI
• Measurement area : LAV (ø 25.4 mm) / Specular component : SCI
• Measurement area : SAV (3 x 5 mm) / Specular component : SCE
• Measurement area : MAV (ø 8 mm)
/ Specular component : SCE
• Measurement area : LAV (ø 25.4 mm) / Specular component : SCE
Calibration for Transmittance Measurements
After the Spectrophotometer has been switched on, 0% calibration and 100% calibration must be performed
before spectral transmittance measurements are taken. 0% calibration is performed by blocking the light
path with an opaque material (a material which has a transmittance of 0%) to set the 0% reference point
for transmittance measurements. 100% calibration is performed using either air (when measuring solid
specimens) or distilled water (when measuring liquid specimens) to set a high-transmittance reference point
for transmittance measurements; in both cases (air and water) the transmittance is assumed to be 100% for
all wavelengths.
{
Since using the LAV target mask and setting the measurement area to LAV and the SCI/SCE setting
to SCI provides the most stable data for transmittance measurements, it is recommended that
transmittance measurements and calibration (both 0% calibration and 100% calibration) for transmittance
measurements be performed under these conditions.
{
The EEPROM of the Spectrophotometer has space for one set of calibration data for transmittance
measurements.
100% calibration data
Because it is necessary to set the 100% transmittance data to the CM-3700A for all wavelengths, 100%
calibration data are normally set to all wavelengths at shipment.
Calibration of Reflectance and transmittance measurements
