Reference
Eight moves chosen because they should generalise beyond the machine they are practised on. That is the design intent and not yet a measured result — no study has been run showing they predict behaviour on unseen equipment. They are what the diagnostic profile measures, and being told you missed one is not much use without knowing what it was.
Every example below is taken from a scenario you can play. None of it is written twice — if a move appears on three different machines here, that is the case for it generalising, made with worked examples rather than an assertion. It is a case, not a proof: the test is whether it predicts behaviour on a machine the technician has never seen, and that experiment has not been run.
3 machines · 14 scenarios
Read what state the machine expected to reach against the state it is in, and treat the gap as the question.
Line 4 case conveyor
the machine's own alarm names the safety string, not the drive or the motor
Performed by: Read the HMI alarm banner.
Conveyor will not startLine 4 case conveyor
the eye reports blocked with nothing in front of it, so the sensing chain is the question and not the product flow
Performed by: Watch the photoeye output as product passes.
Conveyor keeps stopping on a false infeed blockLine 4 case conveyor
the overload tripped on genuine overcurrent rather than nuisance-tripping
Performed by: Measure motor current on all three phases.
Conveyor trips on overloadLine 4 case conveyor
feedback drops out intermittently rather than being absent, which points at a connection and not a failed device
Performed by: Check PLC speed feedback against command.
Conveyor faults intermittently on speed feedbackP-201 transfer pump
flow is HIGH with pressure low, which is a path to somewhere rather than a pump that cannot make pressure
Performed by: Read header flow.
P-201 will not hold header pressureP-201 transfer pump
flow is down as well as pressure, so the instrument is telling the truth and the pump really is passing less
Performed by: Read header flow.
P-201 running but header pressure is lowP-201 transfer pump
the rumble is cavitation, which means starvation rather than wear
Performed by: Listen to the pump and feel for vibration.
P-201 running but header pressure is lowP-201 transfer pump
flow is at design while pressure reads low, which is not physically consistent with a real pressure loss
Performed by: Read header flow.
P-201 header pressure reads low but the process seems fineP-201 transfer pump
the shaft is turning against the arrow on the casing
Performed by: Bump the motor and check rotation direction.
P-201 makes some pressure but nowhere near dutyPK-3 case packer
pressure is correct at rest and sags only under demand, which is a loss rather than a setting
Performed by: Measure regulated pressure while the machine cycles.
PK-3 is slowing down and cases are coming through loosePK-3 case packer
the machine names the exact condition it is holding for
Performed by: Read the sequence step display.
PK-3 stops mid-cycle saying the clamp never closedPK-3 case packer
the switch is on its scribed mark with the band tight, which excludes a knock rather than a failure
Performed by: Inspect the clamp switch mounting and cable.
PK-3 stops mid-cycle saying the clamp never closedPK-3 case packer
pressure falls FURTHER under flow, which is the signature of a restriction and not of a wrong setting
Performed by: Measure regulated pressure while the machine cycles.
Everything on PK-3 is sluggish this morningPK-3 case packer
the machine names the exact condition it is holding for
Performed by: Read the sequence step display.
PK-3 will not clamp at all3 machines · 14 scenarios
Establish where in a chain the quantity is still correct and where it is not, and narrow the fault to the span between.
Line 4 case conveyor
which station in the series string is the open one
Performed by: Walk the E-stop stations.
Conveyor will not startLine 4 case conveyor
the lens and reflector are filmed — the loss is in the optical path, upstream of the electronics
Performed by: Inspect the photoeye lens and alignment.
Conveyor keeps stopping on a false infeed blockLine 4 case conveyor
turning the shaft by hand separates a mechanical restriction from an electrical fault
Performed by: Rotate the drive by hand.
Conveyor trips on overloadP-201 transfer pump
the manual bypass around the control valve is open, which is where the flow is going
Performed by: Check the discharge control valve and bypass.
P-201 will not hold header pressureP-201 transfer pump
suction is in vacuum instead of flooded, which puts the restriction upstream of the pump
Performed by: Measure suction pressure at the pump.
P-201 running but header pressure is lowP-201 transfer pump
8.4 psi across the basket names which part of the suction line is restricted
Performed by: Read the strainer differential gauge.
P-201 running but header pressure is lowP-201 transfer pump
the mA at the input card matches what the transmitter is sending, so the error is at the transmitter and not the card
Performed by: Check the PLC analog input from the transmitter.
P-201 header pressure reads low but the process seems fineP-201 transfer pump
suction is normal, so the pump is being fed and the deficit is at the impeller
Performed by: Measure suction pressure at the pump.
P-201 makes some pressure but nowhere near dutyPK-3 case packer
91 psi at the drop, unmoved by the cycle, which puts the fault downstream of the plant
Performed by: Measure supply pressure at the drop.
PK-3 is slowing down and cases are coming through loosePK-3 case packer
the escape is audible at the clamp rod gland, which localises it to a component
Performed by: Listen along the manifold and actuators for leaks.
PK-3 is slowing down and cases are coming through loosePK-3 case packer
the switch's own output is dark at the switch, so the input card is reporting what it is being told
Performed by: Check the clamp switch output at the switch.
PK-3 stops mid-cycle saying the clamp never closedPK-3 case packer
91 psi at the drop, which puts the loss between the drop and the manifold
Performed by: Measure supply pressure at the drop.
Everything on PK-3 is sluggish this morningPK-3 case packer
the element is loaded and the bowl full, naming both the restriction and why it happened
Performed by: Inspect the filter, regulator and lubricator.
Everything on PK-3 is sluggish this morningPK-3 case packer
shifting the spool by hand cycles the cylinder, clearing air, valve body and cylinder in one action
Performed by: Press the clamp valve manual override.
PK-3 will not clamp at all3 machines · 13 scenarios
Use when it started and what changed to separate wear from failure, and failure from something someone did.
Line 4 case conveyor
when it stopped and what happened immediately before it did
Performed by: Ask the operator what happened.
Conveyor will not startLine 4 case conveyor
a gradual increase in stops rather than a sudden failure
Performed by: Ask the operator what happened, or Read the HMI alarm history.
Conveyor keeps stopping on a false infeed blockLine 4 case conveyor
repeated trips over a period rather than one event
Performed by: Ask the operator what happened, or Read the HMI alarm banner.
Conveyor trips on overloadLine 4 case conveyor
whether this is the first failure or the latest of several
Performed by: Ask the operator what happened, or Read the HMI alarm banner.
Conveyor commanded to run but nothing happensLine 4 case conveyor
that the faults cluster rather than being continuous
Performed by: Ask the operator what happened, or Read the HMI alarm history.
Conveyor faults intermittently on speed feedbackP-201 transfer pump
what was done to the skid before the symptom appeared
Performed by: Ask the operator what changed.
P-201 will not hold header pressureP-201 transfer pump
a gradual slide over days rather than a step change
Performed by: Ask the operator what changed.
P-201 running but header pressure is lowP-201 transfer pump
the reading dropped all at once instead of sliding, which is a step change in an instrument rather than a process degrading
Performed by: Ask the operator what changed.
P-201 header pressure reads low but the process seems fineP-201 transfer pump
that something was apart recently, and what went back together after it
Performed by: Check what work has been done on this skid, or Ask the operator what changed.
P-201 makes some pressure but nowhere near dutyPK-3 case packer
a creep over a week rather than a step change
Performed by: Ask the operator what changed, or Check the cycle time trend.
PK-3 is slowing down and cases are coming through loosePK-3 case packer
that it began suddenly with nobody having worked on the machine
Performed by: Ask the operator what changed.
PK-3 stops mid-cycle saying the clamp never closedPK-3 case packer
a step change over a weekend rather than a creep
Performed by: Ask the operator what changed, or Check the cycle time trend.
Everything on PK-3 is sluggish this morningPK-3 case packer
that it stopped suddenly with no gradual phase first
Performed by: Ask the operator what changed.
PK-3 will not clamp at all3 machines · 3 scenarios
Confirm that supply reached a device before concluding the device is at fault — and know that supply present is not proof the device is drawing it.
Line 4 case conveyor
control voltage reaches the coil, so the wiring to it is intact and the coil is what is not responding
Performed by: Measure voltage at the contactor coil.
Conveyor commanded to run but nothing happensP-201 transfer pump
the motor is drawing a reduced but real load, which excludes a disconnected drive train
Performed by: Measure motor current on all three phases.
P-201 makes some pressure but nowhere near dutyPK-3 case packer
24 V reaches the coil terminals — which proves the circuit got there, not that any current is flowing through it
Performed by: Measure voltage at the clamp valve pilot.
PK-3 will not clamp at all2 machines · 3 scenarios
Separate what the controller asked for from what the field device actually did. A command that was issued is not a movement that happened.
Line 4 case conveyor
the controller issued the start, so the fault is downstream of the command
Performed by: Check the PLC run output.
Conveyor commanded to run but nothing happensLine 4 case conveyor
the drive is following its reference, so the discrepancy is in the feedback path and not the drive
Performed by: Read the VFD status and fault log.
Conveyor faults intermittently on speed feedbackPK-3 case packer
the controller energised its output, so the fault is downstream of the command
Performed by: Check the PLC clamp extend output.
PK-3 will not clamp at all2 machines · 2 scenarios
Compare the affected branch against an equivalent one that is working, and use the difference to localise the fault.
P-201 transfer pump
a local gauge beside the transmitter disagrees with it, which makes this a question about the instrument and not the process
Performed by: Read the local gauge at the header.
P-201 header pressure reads low but the process seems finePK-3 case packer
the pick head strokes on time on the same manifold, so the loss is at one actuator and not in the supply
Performed by: Watch the pick head through a cycle.
PK-3 is slowing down and cases are coming through loose1 machine · 2 scenarios
Decide whether one branch is affected or all of them, and read that as the difference between a local fault and a fault in what feeds them all.
PK-3 case packer
the pick head is slow too, on a different valve, so the fault is in what feeds both of them
Performed by: Watch the pick head through a cycle.
Everything on PK-3 is sluggish this morningPK-3 case packer
nothing is audible anywhere, which removes the other way a pneumatic machine goes short of air
Performed by: Listen along the manifold and actuators for leaks.
Everything on PK-3 is sluggish this morning1 machine · 2 scenarios
Separate an actuator that did not move from a position confirm that did not arrive. The controller reports both identically.
PK-3 case packer
the clamp physically closes while the machine reports it did not — the move happened and the confirm did not
Performed by: Watch the clamp cylinder through a cycle.
PK-3 stops mid-cycle saying the clamp never closedPK-3 case packer
the clamp does not move at all, so this is an actuation fault and not a confirm fault
Performed by: Watch the clamp cylinder through a cycle.
PK-3 will not clamp at all