As for plc, I am a beginner. I will summarize my previous study here for future use. Due to my limited level, there must be many mistakes and inadequacies in this article. Please criticize and correct.
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All the procedures in this paper are written in Step7Template.mwp, and the CPU type is selected from Siemens S7-200 series 226 CN.
First talk about the program, measuring low speed (1000 revolutions per minute): LD I0.0
LD M20.1
CTU C0, +5000 //Set the upper limit of the counter
LD SM0.0
A M20.0
TON T37, +30 // immediately turn on, delay three seconds off
LD SM0.0
O M20.0#p#Page title#e#
AN T37
= M20.0 //Set the T37 timer reset signal
LD M20.0
LD M20.1
CTU C1, +20 //Set the upper limit of the up counter C1
LD C1
MOVW C0, VW200
= M20.2
LD M20.2 = M20.1 //Set the reset signal of the up counter C1. The peripheral circuit is described below. I0.0 is used as the input port. T37 delays three seconds and then gives C1 a signal. C1 counts 1, then T37 is reset, and then delays. After 3 seconds, C1 counts 2,...
Until C1 counts 20. 20 three seconds is one minute. During the period, the pulse signal of port I0.0 is counted by the C0 counter. After one minute, the result is moved to VW200. The pulse signal is obtained by a peripheral circuit.
The above procedure can measure the speed below one thousand, and the upper limit of the experiment is more than 1,400. Since the program uses a low-speed counter, when the speed is high, it is affected by the PLC clock cycle. At one minute, the speed is not recorded, and C0 is cleared, so there is an upper limit. Next, we use the high-speed counter inside the PLC that is not affected by the clock cycle to measure the high speed (more than one thousand revolutions):
LD SM0.1
CALL SBR_0 //Invoke high speed counter initialization subroutine
LD SM0.0
A M20.0
TON T37, +100 //Set the timer value, delay 10 seconds
LD SM0.0
O M20.0 AN T37
= M20.0 // Immediately turn on the delay for ten seconds to disconnect
LD T37
MOVD HC0, VD100 //I0.0 is the high-speed counter HC0 input port, and the counting result is shifted into VD100
MOVD VD100, VD200
MUL +6, VD200 //Count the result multiplied by 6, put in VD200
LD T37
CALL SBR_0 //T37 timed up, call high speed counter initialization subroutine
SBR_0 //High-speed counter initialization subroutine#p#page title#e#
LD SM0.0
MOVB 16#F8, SMB37 //Set control bit: increase count; enabled;
MOVD +0, SMD38 //Load CV
MOVD +0, SMD42 //Load PV
HDEF 0, 0
HSC 0
The above program has a speed range of more than 1000 rpm, and the highest measured value is 2500+ during the experiment. Due to limited experimental conditions, the upper limit is unknown. Someone will have a question: How do you use the measurement for 10 seconds, and then multiply the result by 6 as the speed of one minute instead of directly measuring the speed of one minute? Because the speed result is finally displayed by the digital tube, for the observer, the display after 10 seconds is better than the display after one minute. Finally, we adopted a strategy of 6 times 10 .
Finally, let's talk about peripheral circuits. The peripheral circuit converts the rotational speed into a pulse signal and inputs it into the PLC. The above two programs use the I0.0 port. Hall sensor for signal conversion and acquisition,
Connection method: VCC is connected to 24V, GND is connected to the negative pole of the power supply, A is connected to the signal input terminal I0.0, A terminal and 24V indirect resistor. After the connection, the flat side of the Hall element is fixed to the object to be measured, such as a wheel, and the Hall magnet is mounted on the wheel surface corresponding to the Hall surface. Speed ​​measurement principle: When the wheel rotates once, the magnet and the Hall element are in contact once (actually close), and when they contact, the voltage of the A terminal is lowered, thereby giving the PLC a pulse signal. The distance between the magnet and the Hall is 3 to 5 mm. Pay attention to the front and back of the magnet during installation.
Ok, let's say so much when measuring the speed. After all of the above, the measured data is only placed in the memory of the PLC. We can monitor the PLC operation in the software and see the data. Is it a bit of a hassle, is there a better way to see this data? Of course, LED digital tube can be used to display the data.
