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Callisto

Pulse Counting

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Hi guys, I have a speed encoder on my hands right now that needs to be read from. The speed endcoder generates pulses . So how do I use the siemens PLC to count the pulses and give me the actual speed of the motor setup that I have? Can anybody show me a sample program or give me some tips no how I should go about doing it? I'll be using the S7200 PLC. Thank you regards Edited by Callisto

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Hi, one needs to know : 1)The max frequency you would need to count 2)Whether you would need to run the motor in CW and CCW direction as well. 3)The volatge level of the op from the Encoder 4) type of output from the Encoder These are the basic things once I know these may be I can help Cheers and keep the faith Bapi

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Hi Callisto, Bapi is right, take care about these features. And to program your application, the MicroWin has a Wizard and there you can see/program all steps using High Speed Counter (HSC). Wizard makes it very simple. Take a look there and if you still have questions, please return it here, ok ?? Best regards, Berg

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Hi, Thanks for the reply guys. Do you mean that the High speed counter is only in micro win and not in step 7? The max frequency of my motor is 50hz but since the i would be varying the speed of my motor with a VSD the max frequecny wouldnt be always at 50hz. The output for my encoder would be pulses. I dont know how many pulses per revolution it gives because the manual for it cant be found. The voltage level of the encoder is +5v im still quite new to PLC and thus im quite lost as well. :) Thank you Regards Edited by Callisto

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Hi Callisto, If you'll use S7-200 in your application, you can only use Micro/Win to program this king of PLC. Step 7 Manager is used to program S7-300/400. Well, you told that the max frequency motor is 50 Hz, but it is the frequency of motor's constrution. So you need to know how many poles the motor has or what is the max revolution's motor (rpm). And is essential to know how many pulses your encoder gives per revolution to know the max frequency of pulses. Is the encoder linked directly in the axis or is there a gearbox ? These informations are necessary to especify the correct CPU. For example CPU 224 XP support 200 Khz . And PLC works with 24 Volts, so 5 Volts won't work if you'll connect it directly. I hope I've helped you. Regards, Berg

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Hi Callisto, Berg has given you the directions. If you can give me the codes /make of the "Encoder" may be I can find out the manual for you. Cheers Bapi

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Hi Berg and Bapi I made a mistake.I'm actually using s7300 for my PLC. Yes the frequency for the motor is 50 hz, the motor is a 4 pole machine.And my encoder gives me 500 pulses per revolution and is also linked to the shaft without any gear box.And the encoder needs a supply of 5v. But i just found out that my encdoer isnt working at all...becos i tested it by turning the encoder manually while connected to an oscilloscope but there were no pulses. will work on getting another encoder :) I have another question to ask though. I was told that i am able program the siemens PLC to give an analog output of 10v from the analog output module.Can that be done? I need to do that because i basically need to that to supply my VSD for variation of the motor speed. Regards Callisto

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Hi, You can see more informations about functions modules on Siemens website. But let's see your questions. If your motor has 4 poles and the frequency is 50 Hz, and there isn't gearbox between the motor and encoder, the max. frequency is 12.5 kHz. There is an one-channel counter module (FM350-1) for direct connection of incremental encoder. The counting range is 32 bit or +/- 31 bit and the counting frequency is 500 kHz (if you'll use 5V RS422) or 200 kHz (if you'll use 24 V). You can use 10 V to control your drive. There are a couple of analog modules. The SM322 has 2 outputs (0-10V, +/- 10V, 1-5V, 4-20mA, +/-20mA and 0-20mA) with resolutionod 11 bit + sign and 12 bit others. But if you need more channels you can take another module with more channels. So, that's it. Regards, Berg ------------------------------------------------------

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Hi Berg, I was just wondering. The PLC I'm using is the s7300 cpu 314c-2DP. This means that i would have to use the integrated functions from the integrated modules that the CPU has. Should i be using the positioning integrated function to count the pulses or the counter integrated function to count the pulses? One more thing, i need to generate an anlog signal of 0 - 10 volts from the PLC so that i can control the frequency converter. Do i need to supply an external analog voltage signal to the input of the PLC in order to produce the analog voltage at the output of the PLC? Regards Callisto

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