NIST Traceable Spectral Responsivity
Calibration of Photodiode Detectors
Newport maintains an advanced, fully computer-automated, calibration facility
that has been developed with over 40 years of experience. It is built around a
monochromator-based system that measures the spectral power responsivity of
photodiodes in the 200 nm to 1800 nm spectral region. Newport’s 818 and
918D series detectors are calibrated to ANSI/NCSL Z540 standards using a
NIST calibrated detector (hereafter referred to as the “NIST standard”) of the
same, or similar, type. Newport maintains several NIST standards for various
product types.
Taking into account both NIST’s and Newport’s standard uncertainties and
standard deviations resulting from the calibration process, Newport specifies
the accuracy of its detectors with a 95% confidence level.
D E T E C T O R C A L I B R AT I O N
SYSTEM OVERVIEW
INTRODUCTION
All Newport optical detectors are recommended for a 12 month recalibration
interval. Newport maintains an advanced calibration facility to meet all of your
National Institute of Science and Technology (NIST) traceability needs. In case of
the 818 and 918D series photodiode detectors, computer-automated testing
allows us to include a complete calibration report with every detector and
matching attenuator, if included in the product. In-house reference standards are
directly recertified at every wavelength to the NIST. Our comprehensive
statistical testing, tight control of the measurement environment, and direct
traceability gives you the highest-accuracy calibrations with results you can trust.
This white paper provides an overview of the calibration system and procedure
for calibrating photodiode detectors.
The NIST standards are used to calibrate Newport’s working standard
detectors every three months. The working standard detectors are used to
perform daily calibrations of both production units and re-calibrations of
customer’s detectors. After a calibration, the detector is accompanied by a
hard copy of measurements in the form of spectral responsivity (A/W), over the
entire spectral range for that specific detector
The essential components of a calibration system include a light source, a
tunable monochromator, a working standard detector, a power meter, and,
finally, the detector undergoing calibration (usually referred to as a DUT, or
Device Under Test). Figure 1 shows the basic block diagram of a
calibration system.
NIST TRACEABILITY
To keep the products in compliance with NIST traceability, each new low-power
detector and re-calibration service comes with a full calibration report. The report
lists the measured responsivity at 10 nm intervals across the spectral range
specified for the particular detector. If an attenuator is included, calibration
certification tables are provided for the detector with and without the attenuator.
To ensure quality, Newport always inspects your detector for damage or artifacts
that could affect the accuracy of your recalibration.
Light
Source
Entrance
Optics
Monochromator
PC
Exit
Optics
Detector
Signal
Readout
Figure 1. Detector calibration system block diagram.
DS-041501
Calibration is performed in an environmentally controlled room where the
temperature is maintained at 22°C ± 0.1°C and the humidity is held to a
maximum of 40%.
The calibration process is as follows. The appropriate working standard detector
is put into the calibration system, as depicted in Figure 1. An automated program
is initiated whereby optical power of the broadband light source is measured at
10 nm intervals. Since this detector is a fully calibrated detector, the data is
accurate to within the accuracy specified by NIST, plus the error associated with
transferring the calibration to the working standard. After the power data has
been collected, the DUT is immediately put in the system in the place of the
working standard. This time the data collected is current (in Amps) coming from
the DUT. The current is divided by the corresponding power at that wavelength,
as was measured by the working standard, and the detector’s responsivity is
obtained (the units of responsivity is Amps/Watt).
The NIST traceability chart is given below. In the chart the term “Production
Detector” refers to either a new detector going into stock or a customer’s detector
undergoing re-calibration.
Newport Corporation
1791 Deere Avenue
Irvine, CA 92606
Phone: (949) 863-3144
(949) 253-1800
Fax:
TRACEABILITY CHART FOR NEWPORT
CALIBRATED OPTICAL DETECTORS
NIST calibrates a Newport Detector and generates
an Uncertainty Table, Uncertainty vs. Wavelength
The calibrated detector becomes the
Newport Reference
At Newport's Calibration Lab several Working
Standards are created by calibrating detectors
based on the Newport Reference. The Working
Standards are recalibrated every 3 months. Their
uncertainty table variation versus the uncertainty
table of the Newport Reference is compared with the
process variation values generated by Gage R&R
studies which are done at Newport Corporation. A
working standard is created for each of the Newport
Corporation manufacturing facilities.
At Newport's manufacturing facilities each
production detector is calibrated using the Newport
Working Standard as a reference. An optical power
table is generated, for the full wavelength range of
the detector.
A certificate of calibration is prin ted to confirm
the calibrated detector meets the published
specifications.
Rev. A, 01/17/2011, Instruments Group, PPT Division
NIST CALIBRATION
NIST CALIBRATED DETECTOR
- NEWPORT REFERENCE -
Figure 2. Newport Photodiode
Detector NIST Traceability Chart
NEWPORT
WORKING
STANDARD 1
NEWPORT
WORKING
STANDARD 2
PRODUCTION
DETECTOR 1 CALIBRATED
BASED ON
THE WORKING
STANDARD
PRODUCTION
DETECTOR 2 CALIBRATED
BASED ON
THE WORKING
STANDARD
CERTIFICATE
OF
CALIBRATION
1
CERTIFICATE
OF
CALIBRATION
2
G A ( U ) G E R E P E ATA B I L I T Y A N D
REPRODUCIBILITY (GR&R) OVERVIEW
The Gage Repeatability and Reproducibility (GR&R) is a statistical measure of the
capability of a gauge (or gage) to obtain the same measurement reading every
time the measurement process is undertaken for the same characteristic or
parameter. In other words, GR&R is an indication of a measuring system’s
consistency and stability. It is clear then that high GR&R numbers indicate
instability and are thus undesirable. Lower GR&R numbers are indicative of lower
detector uncertainty. Newport Corporation maintains high standards on our
detector calibration systems in order to minimize the Gage Repeatability and
Reproducibility (GR&R) numbers.
C A L I B R AT I O N M O D U L E S
The calibration information is saved in a memory chip called the EEPROM, which
typically packaged in the connector, permanently fixed or detachable, or in the
housing of the detector. Important information such as the responsivity data,
calibration date, model number, serial number, and any other company proprietary
data is included. One should not forget to return the calibration module along
with the detector for recalibration, if the detector comes with a detachable
calibration module (Figure 3). The calibration module will be reprogrammed
with the new calibration data. Also note that only Newport can update the
calibration module manufactured by Newport Corporation, no other third party
calibration house.
The GR&R has two major components, namely, repeatability and reproducibility.
Repeatability is the ability of the same gauge (detector, in this case) to give
consistent measurement readings no matter how many times the same operator
of the gauge repeats the measurement process. Reproducibility, on the other
hand, is the ability of the same gauge to give consistent measurement readings
regardless of who performs the measurements. The evaluation of a gauge's
reproducibility, therefore, requires measurement readings to be acquired by
different operators under the same conditions.
There are several factors affecting a detector calibration system, including:
1.
Measuring instruments
2.
Operators
3.
Environment
4.
Detector standard
5.
Test Method
All of these factors affect the measurement readings acquired during each
measurement cycle, although to varying degrees. Measurement errors, therefore,
can only be minimized if the errors or variations contributed individually by each
of these factors can also be minimized.
Newport’s detector uncertainty is calculated based on the GR&R study and the
NIST standard.
Figure 3. The /DB Calibration Module (right) and the /CM Calibration Module are detachable from the
detector cable.
Newport detectors are calibrated to internal standards derived from a NIST
calibrated detector of the same type with a tight process and environment
control. Taking into account both NIST’s and Newport’s standard uncertainties
and standard deviations resulting from the calibration process, we specify the
calibration uncertainties of our photodiode detectors surpassing competitors'
specifications.
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Newport's Photodiode Detectors
918D Series Low-Power Calibrated
Photodiode Sensors
Low-Power Calibrated Photodiode
Sensors
Wand Style Calibrated Photodiode
Sensors
Wand Style Calibrated Photodiode
Sensors
Fiber Optic Detectors
Calibrated Integrating Sphere Sensors
For more information please contact Newport Corporation
Application Engineers at 800.222.6440.
Fiber Optic Detectors
Calib