Speed control with encoder feedback

[jeffhansen 0]

Firstly - I'm relatively new to using Omron, having just completed my first project using a CP1H-XA. For my next job, I'm replacing a C1000H with a CJ1G-CPU43H. Most of the code converted straight over, with only a couple of errors due to Analog I/O, but that is not my issue. I'm upgrading an existing installation, and wish to integrate several speed control functions into the PLC. I have a rotary encoder, which I am using as a speed feedback, not for position, so am only going to use the A output, and feeding it into a CT021 counter module. The output is analog 0-10V, DA041 card. So basically, I need to compare the speed input PV to a SV set via the HMI. I've not used the CT021, and I'm finding the manual rather confusing. What I'm looking for is - is there code required to set up the CT021? - What will be the address of the data register for PV? - Should I use PID, and if so, is there an easy way? I'm happy to be pointed toward the right pages of whichever manual. Thanks for your help. Jeff

[dweste 0]

The manual for the CT021 is W401-E1-02 (CJ1W-CT021 High-speed Counter Units OPERATION MANUAL). SECTION 3 is about setup, and SECTION 4 about exchanging data with the CPU. Operating a counter in a nutshell: You have to choose a counter type and a counter signal type. This can be done in the IO table, or direct with DM words. See section 3-2 and 3-3. You have to open the counter gate for each counter. See section 4-2-3. (page 102). Current counter value appears in n+22, n+23 for counter 1, and n+27, n+28 for counter 2. (n = CIO2000 + (Nx10), address of the first word of the block of 40 CIO words that are allocated to the Unit) The DA041 requires similar setup and operation, as described in W345-E1-09 (Analog I/O Units OPERATION MANUAL) Hope this helps :) Edited 26 Aug 2009 by dweste

[jeffhansen 0]

I said I was new to this! I didn't know I could edit in the IO table. Thanks dweste! So...... I'm going to use the CT021 to give me a rate output, by setting the Time Window Rate Measurement to, say, 200mS. I then extract the rate History Date by using IORD #1F01 #00020003 D500 As far as I can make out, this will put the rate measurement for the two counters into D500 and D501. I'm then going to compare the PV with the SV plus/minus a hysteresis factor, and increment or decrement the output to the speed control if required. If I set up a self resetting timer to control the INC/DEC, I can control the rate at which the output changes, thus preventing oscillation. As I don't need precise control, this should do the job, rather than using PID. Looking at it now, I should have just put a 24VDC digital input card in to do the job, as the process is very slow, the encoder pulse frequency is low, and I could have made a simple rate counter in ladder. Any thoughts on this?

[dweste 0]

I never used the rate measurement myself, but it should do the trick. With low pulse frequencies, you could even make your own rate measurement in the PLC, using a normal PLC timer. By then, your CT021 will be obsolete. A normal input card is sufficient when the pulse frequency is very low, AND the PLC cycle time is low. I did it myself one time, but take care! I ended up optimizing the program for cycle time because I missed pulses every now and then. Another option would be the CTL41 counter card, 100kHz instead of 500 kHz (CT021), 4 channels instead of 2 and cheaper.