Experimental Conditions:
Several encoder wheels were sent for analysis. The samples are described below.

50% Sandblasted sample (Zn encoder wheel with 50% of one of the surfaces sandblasted)
Sample 1: Zn plated encoder wheel (not sandblasted)
Sample 2: ABS or POM encoder wheel – 1 sandblasted and 1 unsandblasted wheel
Sample 3: POM encoder wheel – 1 sandblasted and 1 unsandblasted wheel

Specular reflectance measurements at 90 degrees relative to the sample surface were performed on each sample on both the top and bottom sides of the samples. Specular reflectance was measured at 90 degrees with diffuse reflectance measurements for some of the samples at 45 degrees relative to the sample surface using the RPH-1 reflection probe holder. The shiny Zn plated encoder wheels (50% sandblasted sample and sample 1) were analyzed with the STAN-SSH high reflectivity specular reflectance standard as a reference. The dull black encoder wheels (samples 2 and 3) were analyzed with the WS-1 diffuse reflectance standard as a reference. One additional set of data was acquired for the 50% sandblasted Zn plated and POM (sample 3) encoder wheels with the unsandblasted samples used as a reference for the sandblasted samples.

Since the samples had different shapes, various methods were used to acquire the reflection spectra. Measurements of the Zn plated encoder wheels (50% sandblasted and sample 1) were configured as shown in Figure 1 with measurements of the sandblasted and unsandblasted ABS and POM encoder wheels configured as shown in Figure 2. Measurements of the taller POM sandblasted and unsandblasted encoder wheels were configured as shown in Figure 3.

Hardware Used:
HR4000-CG (HR4C349) high resolution spectrometer
DH2000-BAL tungsten deuterium light source
R400-7-UV-VIS reflection probe
RPH-1 reflection probe holder
WS-1 diffuse reflectance standard
STAN-SSH high reflectivity specular reflectance standard
Experimental Parameters:
Zn plated samples (50% Sandblasted and Sample 1)
Integration Time (msec): 45
Spectra Averaged: 50
Boxcar Smoothing: 1

ABS or POM samples (Sample 2)
Integration Time (msec): 375
Spectra Averaged: 20
Boxcar Smoothing: 1

POM sample (Sample 3)
Integration Time (msec): Top 420 Bottom 750
Spectra Averaged: Top 20 Bottom 10
Boxcar Smoothing: 1
Measurement Mode:
Reflectance

Results:
For specular reflectance measurements at 90 degrees, reflectance always decreased following sandblasting. To provide a more quantitative assessment of the decrease, the specular reflectance at 400 nm (wavelength chosen arbitrarily) was compared for the sandblasated versus unsandblasted samples. The results shown in Table 1 are the percent reflectance values at 400 nm for an average of 3 to 5 replicates measurements at different locations on the sample. There was an ~84% difference in specular reflection for the unsandblasted versus sandblasted side of the 50% sandblasted Zn plated encoder wheel. Note (as shown in the last rows of the table) that there was an 8.5% difference in specular reflection when the top and bottom of the unsandblasted Zn encoder wheel (Sample 1) were compared suggesting that there is some variability when various locations on the sample were measured. For the ABS or POM (Sample 2) and POM (Sample 3) encoder wheels, specular reflection differed by 63 to 69% and 41 to 69%, respectively for the sandblasted versus unsandblasted samples. Note that specular measurements from the top and bottom of the same sample varied in most cases. The other data shown in the table is the specular reflection measured for the sandblasted 50% sandblasted Zn plated and POM encoder wheels using the unsandblasted samples as the reference. In this case, specular reflection of the Zn plated encoder wheel at 400 nm was only ~17% of the unsandblasted sample with the POM sample showing a decrease of 45% with sandblasting relative to the unsandblasted POM sample. Specular reflectance data are shown in Figures 4 through 7.

An additional set of measurements was done with the probe placed in the 45 degree position in the reflection probe holder for the 50% sandblasted Zn plated and ABS or POM encoder wheel (Sample 2) samples. Note that the diffuse reflection at 45 degrees was much lower than the specular reflection measured at 90 degrees. The WS-1 diffuse reflectance standard was used as a reference for these measurements. In contrast to the specular reflection measurements at 90 degrees, the diffuse reflectance increased after sandblasting. The data acquired for the 50% sandblasted Zn plated encoder wheel is shown in Figure 8.

Figure 1: Specular reflection measurements of the Zn plated encoder wheels (50% sandblasted sample and Sample 1)

Figure 2: Specular reflection measurements of the ABS or POM encoder wheels (Sample 2)

Figure 3: Specular reflection measurements of the POM encoder wheels (Sample 3)

Table 1: Summary of Specular Reflectance Results

Figure 4: Specular reflection from the 50% Sandblasted Zn Plated Encoder Wheel

Figure 5: Specular reflection from the ABS or POM Encoder Wheel (Sample 2)

Figure 6: Specular reflection from the POM Encoder Wheel (Sample 3)

Figure 7: Specular reflection from sandblasted samples (unsandblasted samples used for reference)

Figure 8: Diffuse Reflection Measurements for the 50% Sandblasted Zn Plated Encoder Wheel