PCC-IV Instruction Manual (Rev. 0.1)
Page 6-24
Section 6
– Blockware Functions
Technical Reference
F59
[SQRT] Square Root
Function
SQRT
provides a 0-100% scaled square root of a 0-100% Input signal. Negative Inputs result in a 0.00%
Block Output. Inputs up to +327% are acceptable. For positive Inputs, the scaling formula is:
Output = 10 * (square root (Input))
Examples:
256% in = 160% out, 49% in = 70% out, 16% in = 40% out, 4% in = 20% out, 0% in = 0% out, -1% in = 0% out
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NAME: SQRT SINGLE USE FUNCTION: N OUTPUT TYPE: A
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Input Type Description Notes
_____________________________________________________________________________________________
1 A INPUT BLOCK
No Parameters
F60
[ABS] Absolute Value
Function
ABS
outputs the absolute value of the Input. That is: for Input > 0, the Output = Input; for Input < 0, the
Output = Input * -1.
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NAME: ABS SINGLE USE FUNCTION: N OUTPUT TYPE: A
---------------------------------------------------------------------------------------------
Input Type Description Notes
_____________________________________________________________________________________________
1 A INPUT
No Parameters
F71
[PID] PID Control (with GAP and ADAPTIVE gain)
Function
PID
is a Proportional, Integral, Derivative cont
rol algorithm. The PID equation used is called the “Parallel”
form by the ISA (Instrument Society of America); others
have used the terms “Non-Interactive”, or “Ideal” form. See
figure below for
PID
logic schematic, see Appendix *** for PID tuning suggestions.
The Proportional constant
is expressed as Gain, as opposed to “Proportional Band”. To convert Proportional Band
(i.e.
“PB”) into Gain: Gain = (100 / PB), or 5% PB is equal to a Gain of 20.00. A numerically larger Gain results in
a larger
PID
output change for the same Process Variable (PV) versus Setpoint (SP) difference.
The Integral constant
is expressed as “Repeats per Minute”. A numerically larger Repeats/min results in a greater
PID
output % per minute ramp change for the same Process Variable (PV) versus Setpoint (SP) difference.
The Derivative constant
is expressed as “Rate Minutes”. A numerically larger Rate Minutes results in a greater
PID
output step change for the same Process Variable (PV) versus Setpoint (SP) percent per minute rate of change.
The Derivative Input is low pass filtered at 1/10 of Rate Minutes to limit the Derivative Kick magnitude.
The optional Setpoint Filter (Parameter 4) can be used to reduce system upsets due to inadvertent rapid Setpoint
changes by the Operator (see note 6).
