User manual

Toolbox 32 User Manual 1.47d www.cse-semaphore.com/mykingfisher
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Set Point: (16-bit register or constant [0 to 32767]) This is the desired process result. The PID output will be
continually adjusted until the Process Variable reaches this setpoint. The setpoint is given the same units or
scaling as the Process Variable and so if an analog input is being monitored the setpoint should have a
range of 0-32760 (0.00 - 100.00%).
Kp Proportional Gain (100 = Gain of 1): (16-bit register or constant [0 to 32767]) The proportional
response is the proportional change in the control variable (the output) in response to a change in the
process variable (the input). Hence, Proportional Response = Kp/100 x (input change). Eg. If Kp=100 then a
change of 3 units in the input will result in a proportional response of 3 units in the PID output. Similarly, if
Kp=200 then a change of 3 units in the input will result in a proportional response of 6 units in the PID output.
Ki Integral Factor (100 = 1rpt/min): (16-bit register or constant [0 to 32767]) The integral response is the
rate of change of the process variable (the output) that will occur after the proportional change in order to
reduce the error between the Set Point and the process variable (the input). Integral response is defined as:
Integral Response [units/min] = Ki/100 x (Input Error). Eg. If Ki=10 and the error is 200, then the integral
response = 10/100 x 200 = 20 units every minute. This means the output will be changed unit by unit up to a
total of 20 units over the minute interval (the output will be changed by 1 every 3 seconds).
Kd Derivative Factor (min): (16-bit register or constant [0 to 32767]) The PID task keeps track of the last
three errors (ie. the difference between the input and the setpoint) and according to the rate of change in the
error will take the appropriate action. This usually results in a dramatic change in the output and so Kd is not
used in many applications. Derivative response is defined as: Derivative Response = Kd/100 x 600/(Sample
Period) x (Error Change). Eg. If Kd=100, Sample Period=10 (1 second) and the error increased by 1 in the
last second (since the PID block was last processed), then the integral response = 100/100 x 600/10 x 1 =
60 units. To disable this function leave Kd set to 0. Note: a derivative factor is not recommended for any
fragile process.
Slew Time (sec): (0=freeze output or 1 to 32767) Slew time is the total amount of time it takes for the output
to go from Output Min to Output Max or vice versa. This should be set to match the slew rate of the
controlled actuator or other device to prevent damage caused by the PID control variable changing too
rapidly.
Sample Period (x 100ms): (0 to 32767) How often the PID block is processed. One unit = 0.1 seconds (100
ms). It is recommended that a minimum setting of 10 be used (ie. Sample Period = 10 x 100 ms = 1 sec) to
allow enough time for the RTU processor to manage communications and other functions.
Direct (0) / Reverse (1): (Bit) This determines whether the Control Variable (the output) will be increased or
decreased for a given error between the Set Point and the Process Variable (the input). The direct action
taken for the various conditions is detailed below:
Control
Type
Process Variable (PV)
(Input) Condition
Control Variable (CV)
Direct Response*
Proportional PV increases CV increases
PV decreases CV decreases
Integral PV > Set Point CV increases
PV < Set Point CV decreases
Derivative Rate of change of PV increases CV increases
Rate of change of PV decreases CV decreases
* For Reverse Action PID, the control variable response is reversed