So What is the Definition of Troubleshooting?
"To isolate the source of a problem and fix it, typically through the process of elimination whereby possible sources of the problem are investigated and eliminated beginning with the most obvious or easiest problem to fix."
When Troubleshooting at your facility remember the following:
Safety Comes First!
You could be around or exposed to;
* Electrical Power Sources
* Aerated Tanks
* Confined Spaces
* Stored Energy Sources - compressed air, water pressure, springs etc.
Ask Yourself is it a CAUSE or a SYMPTOM?
When surveying the situation step back and look at it objectively. Often the problem you first see is a symptom and not the real issue at hand.
Just because you received an alarm from a certain piece of equipment - it is not necessarily the thing that has gone wrong.
To become efficient at troubleshooting you as an operator must understand how the system(s) works. Learning your plant comes with time and experience.
Did your mother tell you not to LIE? - Forget that here, Troubleshooting requires you to L.I.E.
LIST - every cause you can think of associated with the current situation.
INVESTIGATE - starting with the easy things first and working up to the harder ones.
ELIMINATE - potential culprits as you go through the investigation phase
Refer to Electrical As-built Drawings
Refer to Systems Control and Instrumentation OM's (Provided by controls integrator)
Refer to Control Narratives/Strategies
Refer to Electrical Equipment Vendor Manuals
Refer to Mechanical Equipment Vendor Manuals
Refer to System Supplier OM's
Refer to Engineering As-built Drawings
Refer to Engineering Specs
Refer to All Equipment Vendor Manuals
Refer to All System Supplier OM's
Refer to Operations Guide/Manual
Digital Instrumentation Troubleshooting
Switches can be susceptible to improper setup
* Poorly aligned limit switches
* Float switch stuck
* Flow switch installed incorrectly - in reversed
* Look - has field wire failed - corroded, wire nuts fallen off etc.?
* Has switch malfunctioned - got wet, broken?
* Is there a problem at the PLC level?
Alarms can be generated if a signal is broken (normally closed contact is opened) or when the signal is made ( normally open signal is closed).
Electrical Drawings are essential for determining if an instrument is NO or NC.
Always remember - there is usually a valid reason behind why a switch has been activated - and often more investigation is required.
Analog Instrumentation Troubleshooting
* Remember analog instrumentation is critical to the plant and the process. You need to become familiar with the vendor data for each of the analog instruments.
* Analog equipment often runs off a common 24V power supply. Sudden strange behavior in several analog devices at once in your system points to this power supply.
* Analog equipment uses a 4-20 mA signal to communicate with the PLC.
* If you see a problem check the local display on the unit - it will often help narrow down where the problem lies. You can use a multi-meter to test the analog device signal.
If the SCADA/HMI value is suspect and the the local readout seems reasonable, then:
Test the input/output signal at the instrument - is it correct?
Test the input/output signal at the PLC with the one at the instrument - is it correct? If not the field wiring could be compromised.
If the SCADA/HMI value matches the local one but the reading seems suspect, then:
This means the unit is accurately measuring its parameter. In this case the problem lies elsewhere and is probably to do with the units sensor.
It is incorrectly setup - wrong span
It could be a faulty sensor - refer to vendor data for specific device.
Air Operated Automated Valve Troubleshooting
Visually check valve operates when called for in "AUTO"
If not working in "AUTO" - manually operate valve from SCADA/HMI and verify locally.
If both these options have failed, go to the valve and operate the manual override.
If the above three things fail - check the following;
Air supply adequate?
Solenoid valve failed?
Is valve physically jammed?
Rotating Equipment Start Failure
Is there power available? - if no check fuses, this sometimes includes control power fuses located in PLC/Control Panel.
Is the unit in "AUTO" @ the MCC? This sometimes includes a VFD unit as well.
Is the unit in "AUTO" @ the HMI/SCADA?
Try starting unit in "HAND" from SCADA. If it starts in "HAND" but not in "AUTO" check to see if there are unacknowledged alarms or interlocks present preventing the automatic start of the unit.