Cashco 764T Temperature Controller User Manual
Page 11
IOM-764T
11
3. Erratic operation; rapid cycling.
Possible Cause
Remedy
A.
Insuffi cient PB.
A.
Increase PB in 1/8 rev. increments by
turning the needle valve CCW. Reset
set point as required (Max PB at 1-1/2 revs.)
B. Improper air supply.
B1. Supply pressure too high. Reduce airset output
supply pressure to 15-18 psig.
B2. Air supply unsteady. Replace airset.
C. Pulsing process.
C1. Poor location of process temperature tap.
Evaluate and consider relocation.
C2. Steady process, if possible.
D. Non-correctable process dynamics.
D1. Bypass control valve positioner and directly
load
actuator.
D2. Review sizing and characteristic of control valve,
may be oversized. Use restricted trim, ifnecessary.
D3.
Consult
factory.
4. Sluggish operation; slow action.
Possible Cause
Remedy
A.
Restricted
fl ow(s)
A1. Disconnect tubing and blow sensing line.
A2. Check equivalent output tub ing line length against
those indicated herein in Section II.1.c. Relocate
controller, or consider adding an air booster or
positioner at the control valve.
A3. Check for mashed or pinched tubing.
A4. Installation debris. Air-blow lines.
A5. Ice in lines. Use dry air supply.
B.
Insuffi cient air supply.
B.
Increase supply up to 18-20 psig.
C. Too much PB.
C.
Decrease PB in 1/8 rev. increments. Reset
set point as required.
D. Poor sensing location of thermal bulb.
D1. Delete thermal well, if possible. Pack void space
between bulb and well with heat transfer medium.
D2. Evaluate and consider relocation.
E. Too large actuator.
E.
Add on air booster or positioner at the actuator.
F. Use of alcohols, glycols in freezing weather;
F.
Remove sensor sub-assembly and lubricate rings.
dissolved lubricant on O-rings.
5. Calibration erratic; frequent setpoint adjustments.
Possible Cause
Remedy
A. Sensing thermal bulb loose at screwed
A.
Piping weight is cantilevered off of instrument
connection to housing.
air connections causing unscrewing, and
effecting internal clearances. Change piping or
add supports as required. Recalibrate.
B. Air supply debris.
B1. Provide a cleaner air supply or piping source.
B2. Ice in lines. Correct as necessary.
6. Leakage of process fl uid.
Possible Cause
Remedy
A. Thermal bulb and/or thermal well failure.
A1. Chemical attack. Consult factory.
A2. Severe over-temperature. Replace unit.
7. Cannot reach upper or lower temperature levels of stated range.
Possible Cause
Remedy
A. Improper sensor sub-assembly setting.
A.
Remove sensor sub-assembly. Check dimension
to those indicated in Figure 9 . If dimension is
correct, and high setting cannot be reached,
decrease dim"X" by rotating sensor end plate 1/2
revolution CW; reverse for lower setting.