1. Platform MicroLogix1400, A-B PF400 series inverters, pressure sensors, pumps and pumping pipe systems; PLC controls the frequency of the inverter by detecting the pressure feedback signal of the pressure sensor and the given pressure set value, and adjusts the speed of the pum

. Platform

MicroLogix1400, A-B PF400 series inverters, pressure sensor , pump and pumping pipe system; PLC controls the frequency of the inverter by detecting the pressure feedback signal of the pressure sensor and a given pressure setting value, and adjusts the speed of the pump, thereby achieving pressure control.

2. Purpose

1. Familiar with PID instruction

2. Basic applications of mastering PID instruction 3. PID instruction introduction

3: Step

1. Complete hardware connection, and MODBUS communication between PLC and PF400, please refer to Experiment 3. Sensor feedback access PLC analog input I: 0.4.

2. Program description

. Please refer to PID.RSS

3. The file PD110 is a data file of PD type that has been established (there is an element by default, which can be changed through the properties of the data file). All parameters about PID can be found in this PD variable, as shown in Figure 1.

Figure 1

4. The pressure feedback value is calibrated to the input of the PID (0~16383). The sensor is a 4~20 mA signal, and the voltage is converted to 2~10V. Through the PLC's own analog input channel, the most original data range collected by the PLC is 819~4095. The range of the process feedback input of the PID is (0~16383). Therefore, the analog signal can be converted from 819~4095 to (0~16383) through the SCP command, and converted to 0.0~16.0 (unit bar) for

as the actual pressure feedback display. The results are stored in N7:0 and F8:2 (or other addresses) respectively, as shown in Figure 2.

Figure 2

5. Calibrate the pressure setting value to (0~16383) as the setting value input of the PID, and the variable is N7:2, as shown in Figure 3.

Figure 3

6, PID parameter settings

Figure 4

Click on the setting screen on the PID command , which can display a dialog box diagram 5, allowing you to enter additional parameters. These parameters are described below.

Figure 5

When entering parameters, you can type a value, or double-click the parameter bar to browse the available options.

Adjust parameters:

Controller Gain Kc

Type an value . (For 5/02 controllers, the effective range is 0.1 to 25.5. The effective range of 5/03, 5/04 and 5/05 processors is =0 to 3276.7.)

This is the proportional gain. Typically, when the reset and rate terms are set to zero, the gain is set to half of the required value to cause the input to oscillate. Note: When using 5/03, 5/04, and 5/05 processors, RG bit must be set to accept values ​​exceeding 25.5.

	integral gain Ti	Type a value for representing minute .	This is the integral gain. Generally, reset time settings, etc.
	(for 5/02 controllers, the effective range is 0.1 to 25.5. The effective value range for 5/03, 5/04 and 5/05 processors = 0 to 3276.7.)	is the natural cycle measured in the gain calibration above. Note: When using 5/03, 5/04, and 5/05 processors, RG bit must be set to accept values ​​of exceeding 25.5.
differential rate Td	Type a value that represents the value of for minute .	This is a WeChat business item. This value is usually set to upper area
	(for 5/02 controllers, the effective range is 0.1 to 2.55. The effective value range for 5/03, 5/04 and 5/05 processors = 0 to 3276.7.)	time is 1/8 of 0 minutes. Note: RG (reset and gain range) bit does not affect the word.
loop update	Type a representing the value of in seconds . (For 5/02 controllers, the range is from 0.1 to 25.5.For 5/03, 5/04 and 5/05 controllers, there are effects ranges from 0.01 to 10.23	This is the time interval between PID calculations. The input entry is an interval of 0.01 seconds. The normally input cycle update time is 5 to 10 times faster than the natural cycle of the load (the method is to determine it: set the reset and rate parameters to zero, and then increase the gain until the output starts
	0 seconds.)	oscillation) . Note: In STI mode, this value must be equal to the STI time interval value S:30.
Control mode	Select E = SP - PV (reaction) or E = PV - SP (positive).	When the input PV is less than the adjustment point SP, reverse action causes the output CV to increase (e.g., heating application). When the input PV is greater than the adjustment point SP, directly acts on to cause the output CV to increase (e.g., cooling applications).
PID Control	Select Auto ( automatic ) or Manual ( manual ).	Automatic indicates that the PID is in control output. (Word 0, 1, , 0, clear) , manual indicates that the user is setting the output. (word
		0 The 1st bit is set.
time mode	Select Timed ( timing ) or STI.	If timing mode is selected, PID Update its output at the rate specified in the loop update parameters.
			When uses timing mode, your processor scans
		should be at least faster than the loop update time 10 ,
			to prevent timing errors or interference.
		If STI mode is selected, updates its output every time PID is scanned. When you select STI, the PID instruction should be written in STI Interrupt subroutine

			order, the time interval of the STI routine should be equal to the setting value of the PID loop update parameter. Set the STI period in word S:30.
limit output CV	Select to be or No.	Select to be , limiting the output to between the minimum and maximum values. Select no , and no restrictions are imposed on the output.
dead zone DB	Type a value from 0 to scale , or 0-16383 (when scaling does not exist).	This dead zone extends to the adjustment points above and below the values ​​you entered. Enter the dead zone at the zero intersection of the process variable PV and the adjustment point SP. This means that dead zone is only valid when the process variable PV enters the dead zone and passes the adjustment point.

input:

Adjustment point SP	Type a value between 1-16383 or within the valid scaling range.	expected control point for process variables. Enter this value into the 3rd word (word 2) in the control block through your ladder program.
maximum adjustment point	Type an value . (For 5/02	If the set value is read in engineering units, then
(Smax)	controller, the effective range is from -16383 to +16383. The effective range of 5/03 and 5/04 controllers is -32768 to +32767.)	When the control output is 16383, this corresponds to the engineering unit value of the set point.
Minimum adjustment point (Smin)	Type a value . (For 5/02 controllers, the range is from -16383 to +16383. For 5/03 and 5/04 controllers, the effective range is from -32768 to +32767.)	If the set value is read in engineering units, the parameter corresponds to the engineering unit value of the set point when the control output is zero.
Process variables PV	(not editable, only for display)	This is the scale value of the process variable (analog input). If not scaled, the range of this value is 0–16383. Otherwise, the range is the minimum scaling value (word 8) to the maximum scaling value (word 7).

output:

Control output CV (%)	If you selected the manual mode, type a value of 0-16383.	allows you to change the percentage of output control variables.
Minimum output (CV%)	Type a value .	If the limit output CV is , then the value you entered is the minimum output percentage that the control variable CV will get. If CV falls below this minimum, CV will be set to the value you entered and the output alarm lower limit (LL) bit will be set. If the limit output CV is No , the value you entered will determine when to set the lower limit of the output alarm. If CV falls below this minimum, the output alarm lower limit (LL) bit will be set.
Maximum output (CV%)	Type a value .	If the limit output CV is , then the value you entered is the maximum output percentage that the control variable CV will get. If CV exceeds this maximum value, CV sets to the value you entered, and the output alarm upper limit (UL) bit will be set. If the limit output CV is No , the value you entered will determine when to set the upper limit of the output alarm. If CV exceeds this maximum value, the output alarm upper limit (UL) bit will be set.
Measurement error SE	(not editable, only for display)	This is the scaling error selected by the control mode parameters. When using a 5/03 or 5/04 processor, with a scale error greater than 32767 or less than -32767 cannot be represented.

7. Calibrate the PID calculation result (0~36383) to (0~5000), that is, the frequency of the inverter: 0~50Hz), and N7:3 is the final result of the PID calculation. It can be transmitted to the inverter through communication to control the pump speed, thereby adjusting the system pressure in real time, as shown in Figure 6.

Figure 6

8. In order to facilitate observation of the adjustment effect during the debugging process, a pressure trend chart can be established, named PRESSURE, as shown in Figure 7 ; adds the pressure setting value F8:2 and the pressure feedback value variable F8:0 in the attribute screen, as shown in Figure 8. The adjustment screen is shown in Figure 9. The PID adjustment effect when the pressure is given from 6.0bar to 7.0bar.

Figure 7

Figure 8

Figure 9