Overview Delta T is the difference between Terrestrial Time and Universal Time. The following applies: Delta_t = TT - UT1 This parameter can be specified as fDelta_t at the input for function block FB_SPA [ } 13] . It is derived from observations that are continuously reported . A standard value is 66 seconds. Similar products Time switching functions with lower accuracy such as FB_CalcSunPosition and FB_CalcSunriseSunset from TS8010 | TwinCAT 2 PLC Building Automation Basic Documentation last updated: 08.11.2011 TS3900 10 Version: 1.1