Manual And Automatic Operation - Watlow 945 Series User Manual

5. Rate/Derivative Adjustment: Increase rA/dE to 1.00 minute. Raise set point
by 20° to 30°F, or 11° to 17°C, observe the system's approach to set point. If
the load temperature overshoots set point, increase rA/dE to 2.00 minutes.
Next raise set point by 20 to 30°F, or 11 to 17°C and watch the approach to the
new set point. If you increase rA/dE too much, approach to set point will be
very sluggish. Repeat as necessary until the system rises to the new set point
without overshooting or approaching the set point too slowly.
6. Calibration Offset Adjustment: You may want your system to control to a
temperature other than the value coming from the input sensor. If so, measure
the difference between that temperature (perhaps at another point in the
system) and the process value showing in the upper display. Then enter the
CAL offset value you want. Calibration offset adds or subtracts degrees from
the value of the input signal.

Manual and Automatic Operation

To change from manual to auto operation, press AUTO/MAN twice.
Manual operation provides open loop control of the outputs from a range of -100%
(full cooling) to 100% (full heating) power. The 945 allows a negative output value
only with a Cl (Cool) selection on either Ot1 or Ot2. Automatic operation provides
closed loop ON/OFF or PID control. When the operator transfers from a closed
loop to an open loop, the 945 retains the power level from the closed loop control,
referred to as bumpless transfer. When the 945 returns to closed loop control, it
restores the previous set point temperature.
The LED on the AUTO/MAN key indicates auto or manual operation. When the
LED is ON, the control is in manual operation. When the LED is OFF, it is in
Automatic operation. When the LED flashes, press the key again within five
seconds to complete the change in operation.
When a sensor opens the 945 will switch from automatic to manual operation.
• If LOC = 0 or 1 and the conditions for bumpless transfer are met, process
stabilizes within ± 5% of set point within the last two minutes and less than 75%
power. The 945 switches to manual operation at the last automatic power
level.
• If LOC = 2 or 3, or the conditions of bumpless transfer have not been met, the
945 switches into manual operation at 0% power (outputs disabled).
When transferring from auto to manual operation, the control output(s) remains
stable ("bumpless," smooth transition). When transferring from manual to
automatic operation, the control output(s) may change significantly. In manual
operation, the output value appears in the lower display; in automatic operation, the
set point appears.
Tuning and Operating, Chapter 5
Tuning/Operation
WATLOW Series 945 User's Manual
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