26-June-2001

**LABEL:** A unique label to identify the type and
version number of the data base.

**VERSION-DATE:** Self-explanatory

**DESCRIPTION:** Author and brief description of this
version of the data base.

**PITCH:** Measured pitch, based on OGCF
data. Values are more

accurate than suggested by the use 5 significant figures, which are more than sufficient for imaging applications. In all cases the difference between front and back grid pitch is sufficiently small that it can be neglected for imaging purposes.

**PHASE:** As presently defined, this is the
distance, orthogonal to the slits, from the origin of the GF (grid-fiducial)
coordinate system to a mid-slat location as inferred from OGCF data. The origin of the GF coordinate system is
the mid-point between the –X and +X sunny-side fiducials. Phase is positive measured in the –X to +X
sense. . The definition and values of this parameter will be changed to
incorporate displacements of the grid mounting location relative to the imager
axis. Currently tabulated values are
nominal.

**ORIENTATION**: This is the orientation of the slits
relative to a spacecraft-based (imaging) axis.
The values will correspond to the mid-point between the dark and sunny
sides of the grids. Current values are
nominal and have not yet been corrected for grid mounting errors.

**RMSERROR:** The rms deviation of a mid-slit
positions from their ideal locations, assuming a best-fit pitch and
orientation. Based on OGCF data sampled
over the entire active area of the grid.

Measurement errors of ~0.2 microns have been removed.

**SLIT: **For Tecomet grids, this is the
slit width of a single etched layer averaged over all layers and
locations. The values are based on a
consensus fit among on-axis low-energy
x-ray transmission, off-axis low-energy x-ray transmission and far-off-axis
high-energy x-ray transmission data and the reconciliation of a mass model to
weight data. Measurements of individual
layers provide the starting point. For
fuzzy-edged (Tecomet) slits, the slit boundary is defined so that the total
mass of the grids is independent of the SLITEDGE parameter discussed below.

**THICKNESS:** Mechanically-measured average
thickness. For Tecomet, grids, this is
the distance between the outsides of the top and bottom layers. For VBC grids, the values are based on
sample blades.

**SLITEDGE**: Averaging along and over all slits, this is
ONE-HALF of the distance measured orthogonal to the slits over which the
surface density rises from zero to its full value. The value is based on one of two different models, depending on
which gave the best empirical fit to the data set described under SLITS
above. In both cases, the models define
the profile of the surface density as it rises from zero in a slit to its
maximum value in the slat. It is
assumed that along any line of sight perpendicular the grid face, the density
is uniform. Note that the models do not
explicitly reflect the properties of individual layers or stacking. Instead, the models combine the effects of
the edge profile of individual layers, stacking errors and variations in slit
with both within an individual layer and among the multiple layers

For both models, the surface density rises quadratically from zero at each edge of the slit. In Model 1 (indicated by a positive value for SLITEDGE) the surface density profile also decreases quadratically from its maximum value in the slat so as to behave symmetrically with respect to a point of inflection at the 50% point. In Model 2 (indicated by a negative value for SLITEDGE) the quadratic rise from zero surface density in the slit continues until full surface density is achieved, at which point there is a discontinuity in the slope. Note that for model 1, the average totally clear slit width (which determines the low energy response) is

(SLIT-2*SLITEDGE) and the ‘slat width’ with full density is

(PITCH-SLIT-2*SLITEDGE). For model 2, the totally clear slit width is (SLIT- 8/3*|SLITEDGE|) and the ‘slat width’ with full density is (PITCH-SLIT-4/3*|SLITEDGE|).

The SLITEDGE parameter value was found as part of the SLIT consensus fit discussed above

**SLAT-LINEAR-DENSITY:** Excluding bridges, this is the
average linear density of a slat, measured parallel to the slits. (This parameter determines the high-energy
modulation of the grid.)

**TILT:** In the plane orthogonal to the
slits and which includes the imaging axis, this is the angle between the
direction of maximum grid transmission and the imaging axis. It is positive if the line of maximum
response from the grid toward the Sun is directed toward the positive Y axis in
the GF system. Tilt is determined by
the sum of five components: intrinsic
tilt of the slats in the standalone grid; the effects of the grid mounts and their
shims; flatness of the grid trays; relative twist of the two grid trays;
relative displacement of the two grid trays.
The current values include the intrinsic grid values plus the grid
mounts. They do not yet include
tray-related corrections as measured by
the PSI/CMM.

** **

**SPIRAL:** Spiral is the angle between the average
orientation of the sunny-side and dark-side slit orientation, as measured by
the OGCF. When combined with grid
thickness, it is implies a grid-position-dependent tilt.

**SLAT-MATERIAL**: Photon-effective material of the
slats. The effects of epoxy in the
Tecomet grids are not neglected here, but do help determine the grid thickness
and slat-linear density. Note that in
general, the effective bulk density for a given material will vary from grid to
grid.

**BRIDGE-MATERIAL:** Photon-effective material for the
bridges. For the VBC grids, this is a
weighted average of the metering structure and spacers, with the Beryllium
content neglected. Adopted Fe:Ni:Cu
composition ratios by weight for FeNi, FeNiCu and Invar are: 91:09:00, 34:18:48
and 64:36:00 respectively. Small
differences among grids 6,7,8 bridge composition have been neglected.

**BRIDGE-PERIOD:** Effective period of the bridge
structures. For Tecomet grids, these
values are not exact, but the ratio of bridge-width to bridge-period is
believed to be ok. For VBC grids, the *effective*
bridge period is dependent on incident angle and is also different for front
and rear grids. The values shown is an
effective average over incident angles from 0 to 30 arcminutes.

**BRIDGE-WIDTH:** The width (parallel to the slits) of
the bridge. This is based on a model in
which the bridge is a rectangular bar of uniform composition. For Tecomet grids, this is based on the
area of a single layer bridge divided by the slit width. The same SLIT-EDGE parameter is also assumed
to apply to bridges.

**BRIDGE-HEIGHT:** The height (parallel to earth-sun
line) of the bridge model.

Note that for the VBC grids, the bridge model assumes a single rectangle which incorporates the effects of both top and bottom metering structures and their spacers. The bridge height and width is chosen to reflect the outer envelope of the metering structure and spacers, averaged between slats.

**BRIDGE-LINEAR-DENSITY:** The linear density of the bridge
model along each bridge. The linear
density is chosen to reflect the average amount of material between slats with
the caveate that this material is also superimposed on the slats. The resulting overestimate of material
where the slats are has little, if any effect.