When using Quadtone RIP to generate digital negatives for alternative processes, you need to supply your process calibration curve to the RIP using the GREY_CURVE field in the QTR ink description file.
The following Photoshop javascript and stepwedge can be used to automatically build the Photoshop curve for use by QTR.
Installation
To install the script copy it into your Photoshop Presets/Scripts directory. The script only works with Photoshop CS3 or greater.
Usage
Load the stepwedge in Photoshop, invert and horizontally flip it, then print it on your chosen transparency material using QTR. Print the stepwedge negative using your preferred process. Scan the resulting print without any scanner adjustments and load into Photoshop. Crop the stepwedge scan so it looks exactly like the original stepwedge. Run the Build QTR Curve Photshop script, under File->Scripts, which measures the printed stepwedge and builds a Photoshop curve you can save and use in QTR.
Update 2019
The script will now display the coordinates of the curve in a dialog box where they can be copied and directly pasted into the GREY_CURVE field.
Workshops
Kerik Kouklis teaches the QTR method and uses this script in his workshops on Platinum, Gum over Platinum and Digital Negatives.