Preferred FlexFit 110 - ... Not at Position Lockouts; Possible Reasons for a... Not at Position Lockout

Troubleshooting – "... Not at Position" Lockouts 5-87
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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conduit (out of sight), which allow the shields to connect to the conduit. Shields connected at both ends, or with unintentional
second grounds, add extra noise to a signal instead of reducing noise!
• To prevent noise pick-up, shielded cables should never be run in conduits or trays with AC wiring (any voltage). There
are only 3 exceptions to this rule, as detailed on the eld wiring diagram (scanner, servos, and the ZP Oxygen Analyzer).
• Ignition transformer pilot spark wiring is particularly noisy. If any problems occur during the time that the spark is active,
replace the pilot high voltage wire with automotive grade noise suppression spark plug cabling (either resistance core or
spiral wound 'Mag' core cable).
• The load wires that connect a VSD to the motor contain massive amounts of electrical noise potential during normal
operation. Carefully read and scrupulously follow all notes for this wiring, as shown on the eld-wiring diagram. Modern
shielded 3 phase wiring cables with integral grounding wire(s) are now available from Belden, Alpha, and others to further
reduce this electrical noise. Improperly shielded VSD generated noise can/will travel through the boiler and building steel
and can affect both 120 VAC and low voltage signals in conduits that are far away from the VSD load wiring.
• If the electrical installation appears to be in accordance with all the above practices, and sporadic problems are still occur-
ring, the power problems in other parts of the facility might be causing electrical noise in the AC power supply. Harmonic
distortion surges, spikes, and drop-outs are common problems in plant power distribution systems today. 120 VAC line
voltage conditioners from Control Concepts, Sola, or Preferred p/n 70438 (or 70439) can help reduce this noise. More
exotic line conditioning power transformers and some UPS systems are also possible solutions.
"... Not at Position" Lockouts
The following are considered fuel-air ratio control devices, and can cause a "Not At Position" lockout:
• Servos: Fuel 1 Valve, Fuel 2 Valve, F1/F2 Valve, FD Fan Damper, FGR Damper, Aux 1, Aux 2, Aux 3
• VSDs: FD VSD, Aux 2 VSD
The FlexFit reads the position (or VSD speed) feedback of all these devices every 0.5 seconds and determines the deviation
between the actual position and the established on-curve setpoint. A "… Not at Position" lockout occurs if any device's deviation is
more than twice its deadband (or 0.3 degrees, whichever is larger) for longer than 3.5 seconds.
"... Not at Position" Lockout Exceptions
• This lockout does not occur during the standby state or when already in lockout for some other reason.
• This lockout does not occur when in commission mode except when in the verify points mode.
• The duration is extended to 20 seconds during the following transitions:
◦ MTFI to modulate
◦ Upon exiting commission mode
◦ Upon activating the verify points mode when in commission mode
Possible Reasons for a "... Not at Position" Lockout
• Mechanical binding of the coupling, valve, or damper to which the servo is connected.
Review the Lockout Data to see if it re-occurs consistently at the same approximate position.
Re-align the mounting to reduce coupling binding.
• Undersized Servo – insufcient torque
Widening the servo deadband can be a temporary solution for medium-to-low-performance burners.
• Loss of 120 VAC to the servo
Loose wiring
• Loss of feedback signal to the FlexFit
Loose wiring
• FD VSD or Aux 2 VSD internal rate limiting is slower than the setting of parameter "P2.1.3 Ramp Rate Sec/30Hz, FD VSD"
or "P2.2.3 4-20 Ramp Rate Sec/100%, Aux 2" on page 4-67.
The Parameters must be set to a slower ramp rate than the slowest VSD ramp rate.
This is a manual setting that must be set by the start-up technician.
• FD VSD or Aux 2 VSD Hz feedback 4-20 mA signal calibration doesn't match the required 0-60Hz/4-20mA.
Adjust the VSD 4-20 calibration feedback or deadband. See the parameters for "Fuel-Air > FD VSD" or "Fuel-Air >
Aux 2" on page 4-66.
• The torque requirement for the valve has changed over time (i.e., dried grease, stiffened valve), causing a decrease in
servo speed (Error E17 on servo LCD).