Why isn't point-to-point checkout done from the graphics?
By Bassirou Thiam, building automation engineer · Updated
Because the graphics sit on top of the control system. Point-to-point checkout proves that each wire, device and controller I/O works, even if everything above it failed. Checking from the graphics mixes two possible causes for every fault, the graphic mapping or the controller I/O, and needs a finished network first.
The right order
- Point to point: wire intact, landed on the right device, device sending and receiving the right signal, controller I/O configured. Points are forced by hand, ignoring the program and the graphics.
- Program: it matches the accepted sequence, including cases the sequence did not spell out.
- Graphics: top to bottom, every link checked and unused points removed.
Why the graphics still need a check
A sensor swapped on a graphic does not change how the program runs, so point to point at the controller will not catch it. Graphic mapping errors are found by checking the graphics themselves once they exist: once internally, then with the witness.
Sources
Related
GuidesWhat goes in a BAS points listThe columns a BAS points list needs, the BACnet point types, and a method to build it from the control schematic. Free Excel template included.
GlossaryWhat is an I/O point in building automation?Definition of an I/O point in building automation: a physical input or output wired to a controller terminal, as counted in the points list.
GlossaryWhat is a DDC controller?Definition of a DDC (direct digital control) controller: the field device that reads inputs, runs the sequence and drives outputs for HVAC equipment.