TIDA-00554 DLP NIRscan™ Nano EVM Stand-off HeadNovember 2016

Stand-off Head Design for DLP® NIRscanTM Nano EVM

Introduction
The DLP® NIRscan™ Nano Evaluation Module (EVM) employs a diffuse reflectance design that
requires the sample to be placed in direct contact with the sapphire window. This design was chosen toensure proper illumination of a sample by the built-in lamps.
Since the release of the DLP NIRscan Nano EVM, many requests have been received for a design thatwould allow diffuse reflectance measurements without direct contact with the EVM window. Such adesign would allow for the measurement of many substances that would otherwise result in residue
being left on the window.
The following are examples of such substances:• Food:- Fruits – Grapes, strawberries, apples, and others that can have sugar residues on the surface- Dairy products – Ice cream, yogurt, cheeses, sour cream, and other dairy products- Desserts – Applesauce, pudding, and pastries• Industrial fluids and lubricants• Soil and fertilizers• Cosmetics• Pharmaceuticals
Larger sampling area is another advantage of a stand-off design, particularly for items such as grain orother substances with short range inhomogeneity. A larger area will integrate these differences
allowing measurement in an environment where it is not feasible or desirable to place the samples in
direct contact with the window.
TI has designed a prototype of a simple telescopic stand-off head which was tested to determine theusability and characteristics of the design.

1Lit. NumberResults
Figure 1 shows the absorbance spectra of Comté cheese taken at two distances, and demonstrates
the similarity of the spectra.
21.8
1.6
1.4

Lo g 1 /R

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0.20900

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Wavelength, nm

Figure 1 – Comté Cheese Absorbance at 10 mm and 15 mm

Relative Energy

Figure 2 shows the raw detector readings of Spectralon™ at 10 mm – 50 mm and demonstrates theconsistency of the data shape. The readings only differ by a scaling factor from one another.

900

10 mm
20 mm
30 mm
40 mm
50 mm

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Wavelength, nm

Figure 2 – Reflected Energy of Spectralon Surface at 10 – 50 mm2®

Stand-off Head Design for DLP NIRscanTM Nano EVM

1700

Lit. NumberConsiderations
The primary considerations for a stand-off head are signal-to-noise ratio (SNR), and illumination
intensity.
SNR

Rela t iv e SNR

Figure 3 shows the relative SNR values from data taken at 10 – 50 mm with the illumination intensity
fixed. For a given illumination scheme, the maximum working distance will be determined by therequired SNR for the system. The SNR falls off as an exponential of the form SNR = k·e-c·x, where kand c are constants. The best fit exponential curve is shown in red.

-c·x

SNR = k·e

R² = 0.9905

0102030405060Sample Distance, mm

Figure 3 – Relative SNR at 10 – 50 mm [ 9V illumination, 22 sec (99 scans) ]Illumination Intensity
If the illumination level does not achieve the desired working distance for the required SNR of thesystem, then the illumination can be increased. The trade-off is power consumption.
The on board lamp driver is based on the TI OPA567 power amplifier. In this system the supply is 5V
and is designed to limit the current to 280 mA in order remain within the USB 2.0 power draw
specifications. If more power than this is needed the circuit can be designed to put out up to 1 A, but aseparate 5V supply will be needed. See § 3.1 of the Application Report Signal Chain Performance
Optimizations in the TI DLP® Technology-Based Spectrometer for further information.
NOTE: If more intensity is desired than can be supplied by the on board lamp driver, then a separate
lamp supply should be employed.

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Stand-off Head Design for DLP NIRscanTM Nano EVM3Lit. Number

DesignThe design includes CAD files for the head, and can be printed with a 3D printer and populated withthe lenses specified in the design.
The design also includes a simple Zemax model showing the area that will be captured by the slit at
the distance chosen. This model can be modified if different lenses are chosen or if a larger working
distance is needed
Figure 4 shows the Zemax model layout of the module. Notice in this arrangement that the slit isimaged at 16.5 mm from the front of the end face of the mechanics. The area seen by the slit here is
only 1.7 x 0.6 mm. If you intend to work at this distance and need a larger sample area, the separation
between the lens sets will need to be increased or decreased to provide more defocus at this distance.

slit

Figure 4 - Zemax Stand-off Module Layout [10, 16.5, 35 & 50 mm]

Figure 5 shows the shape of the sampling area (area seen by the slit) at these distances.
10 mm Sample Distance

16.5 mm Sample Distance

3.7 x 2.9 mm

1.7 x 0.6 mm

35 mm Sample Distance

50 mm Sample Distance

11.8 x 8.1 mm

20.0 x 14.7 mm

Figure 5 - Zemax Sample Area Shape [10, 16.5, 35 & 50 mm]

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Stand-off Head Design for DLP NIRscanTM Nano EVM

Lit. NumberRelated Documentation from Texas Instruments
•••••
•
•

DLPC150 Data Sheet: DLPC150 DLP® Digital Controller for Advanced Light Control, TI literature
number DLPS048
DLP2010NIR Data Sheet: DLP2010NIR (0.2 WVGA Near-Infrared DMD), TI literature numberDLPS059
Programmer’s Guide: DLPC150 Programmer’s Guide, TI literature number DLPU031
Application Note: Texas Instruments DLP® Spectrometer Design Considerations, TI literature
number DLPA049
Application Report: Flexible Trade-offs in Maximizing SNR and Resolution in TI DLP® TechnologyBased Spectrometer Systems, TI literature number DLPA066
Selection Guide: TI DLP® Technology for Spectroscopy, TI literature number DLPT020
Application Report: Signal Chain Performance Optimizations in the TI DLP® Technology-Based
Spectrometer, TI literature number DLPA072

If You Need Assistance
Refer to the DLP Products and MEMS TI E2E Community support forums

Trademarks
DLP is a registered trademark of Texas Instruments.
NIRscan and E2E are Texas Instruments trademarks.

REFERENCES[1] Haibach, F. G., “Getting the best results from nir measurements,” tech. rep., BaySpec Incorporated(2014).

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Stand-off Head Design for DLP NIRscanTM Nano EVM

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