As mentioned above, the HXDS has three subsystems, BND-500, BND-H, and HXDA. Both the BND-500 and BND-H will monitor the beam flux output. The BND-500 has a fixed SSD, and a FPC mounted on a moving stage. The SSD will have four circular apertures of diameter 0.2, 0.5, 2.0, and 5.0 mm, respectively, and the FPC will also have four circular apertures of diameter 1, 4, 12, and 36 mm. The BND-H has three fixed FPCs and one mapping FPC. The four BND-H FPCs all have 1.44" x 4.88" rectangular apertures (with rounded corners). The mapper FPC has an additional 36-mm-diameter aperture which can be flipped into position on top of the larger rectangular aperture. HXDA has one SSD, two FPCs, and one HSI. There will be a set of apertures for SSD, and another set for the FPC.
The energy resolution of an SSD varies with the shaping time constant of its electronics. As an example, if the event rate is less than 5000 cts/sec and a 2 microsecond shaping time constant is used, the FWHM will be 190 - 230 eV over the energy range 0.5 - 10 keV. The maximum count rate of a SSD was designed to be 20,000 cts/sec, and it has been demonstrated up to 10,000 cts/sec. The background is less than 0.3 cts/sec. For a FPC, the quantum efficiency depends mostly on the gas absorption efficiency and window transmission. FPCs have poor energy resolving powers which range from 0.2 to 2 over the range 0.1 to 10 keV. The FPC maximum count-rate was also designed to be 20,000 cts/sec.
The HSI is a microchannel plate detector. It has an imaging area of about 18 mm in diameter. The HSI has a 10 micron pore size, a 6 micron position read out accuracy, and 20 micron imaging resolution (FWHM). As its name indicates, it was designed to handle higher count rates than HRC. The designed maximum count rate is 2000 cts/sec for the entire plate, and 40 cts/sec for each pore.