图解SLC 和MicroLogi 系列AB LC的PID指令编程技巧

图解SLC 500/MicroLogix 系列AB PLC 的 PID 编程编程使用方法使用方法使用方法：：
附：SLC PID 编程编程的技巧和帮助的技巧和帮助的技巧和帮助（（英文英文））：
SLC PID Programming Tips & Help
1. Ideally, the rung condition should be unconditional. If the rung condition is toggled, the RATE and RESET terms are zeroed out. This is typically undesirable.
2. The Process Variable must not exceed a value of 1638
3. This is typically accomplished using a SCL or
SCP instruction. If a 1746-RTD or 1746-NT4 is used to provide a process variable in engineering units, the value can be moved directly to the Process Variable without any scaling. Be sure to enter the Set Point in the same format as the Process Variable or module is configured. Engineering units on one of these modules will convert the analog signal into degrees F or C depending. Defaulte is deg F. So an entry of 300 deg F into the Process Variable will close the loop on a Set Point of the same scaling (ex. 315 deg F ) with no external or internal scaling.
3. Setpoint Min. (SMIN, word 8) and Setpoint Max. (SMAX, word 7) are defaulted to 0 which represent a range
of 0 to 16383 respectively. No Setpoint Scaling: Setpoint Min. and Setpoint Max. are both 0 or contain the values 0 to 16383 respectively, then the SETPOINT (word 2) must be entered as a value between 0 to 16383.
With Setpoint Scaling: Setpoint Min. contains the value which represents the MINIMUM engineering unit of measure, and Setpoint Max. contains the value which represents the MAXIMUM engineering unit of
measure. Therefore your SETPOINT must be entered in same engineering units defined by the SMIN and
SMAX parameters, and must not be entered as a value outside of their boundary. For example: If you are using an analog input of 4 - 20 mA and you select engineering units in the channel configuration. then your result will be from 4000 to 20000 counts. 20,000 into the Process Variable will cause a PID fault. This must be externaly scaled with the SCP instruction or the channel data format changed to Scaled for PID. Then the SMIN and SMAX can be used to convert the value into engineering units. However, doing both will "double" scale the value and the pid will never operate correctly. If external scaling is used, the leave SMIN and SMAX at zero.
4. The OUTPUT of the SLC PID instruction can be monitored at two different locations: the Output CV %
(word 16 of the control block) and the Output CV. The Output CV can also be changed by the operator by placing the PID in Manual mode, by setting bit 1 of the 1st word of the control block, or by using the Manual function key on the PID configuration screen and entering a value between 0 and 16383. The Output CV % has a range of 0-100% and cannot be changed by the operator.
5. When the PID is in the MANUAL mode, the output value must be entered into the integer word you declared
as your Control Variable when you entered the PID instruction. This value must have a range of 0 to
16383.
NOTE: The manual value is never written to word 16 of the PID control block.
6. The Output CV is usually always sent through a scaling instruction so its 0-16383 value matches the input
range of a particular analog output module. There is an example program in the PID chapter that illustrates input and output scaling.
7. Error code 0036H is declared when a particular action is contrary to the rules of the SLC PID instruction.
Most of these infractions are described on a page in the PID chapter as Runtime Errors. Each error has a two-digit Sub Error code associated with the problem and is displayed in the MSB of word 1 of the control block (the 2nd word of the control block). However, there are times when the processor will fault with a 0036H error code but no Sub Error code is displayed; normal trouble-shooting practices and knowledge of the instruction is required to determine the cause in these cases.
8. The 5/04 and 5/03 processors use the same SLC PID algorithm; the 5/02 uses a less powerful algorithm
which has restricted control block ranges as described in the PID chapter.
9. In order to prevent an INTEGRAL wind-up condition:
o Set OUTPUT MAX (word 11) to a value of 100.
o Then ENABLE "Output Limiting" by setting Bit 3 in Word 0.
o When the CV output reaches 100% (or 16383) the PID stops calculating the INTEGRAL TERM, which prevents the unwanted wind-up.。