For most applications, the LI200X has replaced the LI200S. The LI200S is essentially the same sensor as the LI200X except it does not have the same completion circuit to scale its output voltage. A unique calibration entry for each probe is required. Campbell Scientific does not record these original calibrations, but LI-COR, the manufacturer, does; contact Beth McCulley (800) 477-3576. You'll need the pyranometer's LI-COR serial number (on sensor housing); should begin with the letters PY...