UPd3 exhibits four antiferroquadrupolar (AFQ) ordered phases below T0=7.6K. We have determined their order parameters using resonant x-ray diffraction. UPd3 has the dhcp crystal structure, with U4+ ions at sites with locally (a) hexagonal and (b) quasi-cubic symmetry. The primary order parameters involve the U quadrupole moments on the quasi-cubic sites. The uranium 5f2 electrons in UPd3 are well localised. Early theories proposed singlet ground states on both sites, in order to explain the absence of magnetic ordering. However, we have shown that this is incompatible with the observed AFQ order, and proposed a new model with a doublet ground state on the quasi-cubic sites. The main aim of this proposal is to explore the predictions of our new model by measuring the excitations in UPd3 at temperatures above and below T0.