Some blocks ... AIN, AOUT, PID, etc ... have obvious counterparts in standard diagramming. But CALC, LOGIC, PLB, seq blocks and others do many functions which would normally be single elements in a control diagram. I would normally diagram the block as a single element with a breakout detail showing the internal logic. Brad Wilson Process Control Engineer ExxonMobil Chemical Co Edison Synthetics Plant 732-321-6115 732-321-6177 fax Brad.S.Wilson@xxxxxxxxxxxxxx _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: //www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave