P
AGE
39
Manual Tuning Method 3.5
1. Cycle Time - Time Proportioning Outputs
A. Adjusting the cycle time affects instrument operation
1. Shorter Cycle Time
a. More accurate control
b. Shorter life span of electro-mechanical components
2. Longer Cycle Time
a. Less control accuracy
b. Longer life span of electro-mechanical components
2. Proportional Bandwidth
A. Proportional Bandwidth is the inverse of gain.
Increased Bandwidth = Decreased Gain
B. Increase the Proportional Bandwidth if:
1. The process overshoots excessively.
2. The process oscillates excessively.
C. Decrease the Proportional Bandwidth if:
1. The process responds slowly
2. The process fails to reach setpoint
3. Add Automatic Reset
A. Increase the Automatic Reset in steps of .2 repeats per minute until the
process becomes unstable, then decrease until stability is restored.
B. Be sure to allow sufficient time for the process and the instrument to react.
4. Rate Adjustment
A. Rate can cause process instability. Typically add Rate as 1/10th of the
automatic reset value.
B. Decrease Rate if:
1. The process overshoots/undershoots
2. If the process oscillates excessively
5. Manual Reset
A. After making all other adjustments, use if an offset exists between the
setpoint and the process variable.
B. If the process is:
1. Below setpoint use a positive Manual Reset value equal to the
difference.
2. Above the setpoint use a negative Manual Reset value equal to the
difference.
