Manual
Watlow Series 935A User’s Manual 33
Fine Tune the PID Settings
1. Set [Pb`h] and [Ct`h] in degrees.
2. If Proportional Band Heat [Pb`h] = 0, Set Hysteresis Heat [HySh]. The Series 935A will provide on/off
control with the hysteresis value selected, and no proportioning action.
3. Proportional Bands should be decreased for tighter control but increased to eliminate oscillations.
4. Cycle Time Heat [Ct`h] is limited to a minimum of 5.0 seconds for the electromechanical relay to help
reduce wear. The electromechanical relay (D, Output 2) is not recommended for PID control. It is war-
ranted to 100,000 contact closures only. Alarm or on/off control are appropriate applications for the
Series 935A's electromechanical relay output.
5. Set Dead Band [``db] to adjust the effective cool set point above the primary set point by the dead
band value in degrees. In cool/heat applications, dead band prevents continuous cool output action by
creating a buffer between heating and cooling output action.
6. Set [Pb`c] and [Ct`c] in degrees.
7. If Proportional Band Cool [Pb`c] = 0, Set Hysteresis Heat [HYSc]. The Series 935A will provide on/off
control with the hysteresis value selected, and no proportioning action.
8. Proportional Bands should be decreased for tighter control but increased to eliminate oscillations.
9. Cycle Time Heat [Ct`h] is limited to a minimum of 5.0 seconds for the electromechanical relay to help
reduce wear. The electromechanical relay (D, Output 2) is not recommended for PID control. It is war-
ranted to 100,000 contact closures only. Alarm or on/off control are appropriate applications for the
Series 935A's electromechanical relay output.
10. Set Integral [``It] to eliminate droop in the system. Lower the value for more droop reduction.
Adjustable from 0 to 99.9 minutes / repeat.
11. Set Derivative [``dE] to prevent overshoot. Increasing the value slows the approach to set point.
Adjustable from 0 to 9.99 minutes.
12. Calibration Offset [`Cal] eliminates the difference between the displayed process temperature and the
actual process temperature value.
PID Menu
Set up Heat:
[Pb`h]
✓
Proportional Band
[hySh]
✓
Hysteresis
[Ct`h]
✓
Cycle Time
[``db]
✓
Dead Band
Set up Cool:
[Pb`c]
✓
Proportional Band
[hySc]
✓
Hysteresis
[Ct`c]
✓
Cycle Time
Set up General:
[``It]
✓
Integral
[``dE]
✓
Derivative
[`CAL]
✓
Calibration Offset