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Hz of inputs module

Created by: fededalma at: 7/22/2013 11:11 AM (7 Replies)

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7/22/2013 11:11 AM	Rate (0)
fededalma Regular Member Joined: 3/29/2013 Last visit: 5/19/2023 Posts: 4 Rating: (0)	Hello everyone, does anyone know how many hz can do a normal input modulefor S7-1200 plc? I can't find it on datasheets. Thank you.
	Last edited by: fededalma at: 7/22/2013 11:56 AM Last edited by: fededalma at: 7/22/2013 11:33 AM
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7/22/2013 11:47 AM	Rate (0)
Nelliyan randy Posts: 461 Rating: (29)	Hi check the document 1st page NOTICE. Seems like up to 20 khz can be used.. Make sure & wait for others suggestions & answers Regards, Nelliyan.G Attachment SB.pdf (751 Downloads)
Nelliyan randy Posts: 461 Rating: (29)	Last edited by: Nelliyan randy at: 7/22/2013 12:05 PM
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7/22/2013 12:13 PM	Rate (0)
fededalma Regular Member Joined: 3/29/2013 Last visit: 5/19/2023 Posts: 4 Rating: (0)	Thank you very much! But for these inputs module the frequence is specified on its datasheet. What about, for example, theSM1221, 6ES7221-1BH32-0XB0 ? I can't find specifications about this.. why? And why on the SB that you show me, instead, the hz valueis shown everywhere?! Thank you again.

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7/23/2013 8:45 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	I do not have the absolute answer you seek. But I am curious as to why this is important to you. The onboard inputs are interruptable and thus can be used at a higher rate. For extended inputs, my rule of thumb would be that the input update can not be bargained on beyond the cycle speed of your PLC. These inputs have a communication link to the CPU. You do know that the inputs you read is a buffered reading. You can read directly but there is a special command for this. Also the inputs also have filtering (debouncing). If you want more fast inputs, I would recommend for you a SB (signal board); some can read up to 200kHz. Could you explain please why this input speed is of inportance to you? w PS: The filter for a SM card can be set as low as 0.2ms. I doubt that the actual throughput will be quicker than that. The throughput speed will also be influenced by how many SM cards is connected onto the internal communication bus of the PLC system. Your input filter will force you to have a input pulsing speed of more than 0.2ms -- or smaller than 5kHz / 2 = 2.5Khz. Will this help then? With a safety margin you can say 1kHz if the filter is set to 0.2ms. [Does the S7-1200 have pulse catching / pulse stretching as the S7-200 has?]
William_B Posts: 5225 Rating: (1196)	Last edited by: William B. at: 7/23/2013 8:58 PM post script added
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7/24/2013 8:47 AM	Rate (0)
fededalma Regular Member Joined: 3/29/2013 Last visit: 5/19/2023 Posts: 4 Rating: (0)	Thank you William. Ok, my target is to read the RPM of a wheel. The person who has realised a program similar to mine, before me, tried to use the integrated high speed counter of the plc Siemens 1214. The result? When the wheel was running at costant speed the counter was writing everytime different values, like670 RPMand 1 second after 830, after 900, after 750 ... nonsense!! We still haven't found a reply to this problem. So I was looking to use a "normal" input. Have you got the same problem? Or have some suggestions? Thanks

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7/24/2013 8:56 AM	Rate (0)
Nelliyan randy Posts: 461 Rating: (29)	Same isuue i faced last month... { my mistake i should have asked ur requirement , it would be easier... thanks to William } C the similar post & thing may helps u /tf/WW/en/Posts/92810#top Sensor selection is a major fact that troubled me ,, So confirm whether the switching frequency of ur sensor s higher than the switching frequency of ur load [ if the selection was wrong it surely leads to the wrong readings ] Regards, Nelliyan.G
Nelliyan randy Posts: 461 Rating: (29)	Last edited by: Nelliyan randy at: 7/24/2013 8:58 AM
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7/24/2013 3:29 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/15/2024 Posts: 15402 Rating: (2443)	fededalma Thank you William. Ok, my target is to read the RPM of a wheel. The person who has realised a program similar to mine, before me, tried to use the integrated high speed counter of the plc Siemens 1214. The result? When the wheel was running at costant speed the counter was writing everytime different values, like670 RPMand 1 second after 830, after 900, after 750 ... nonsense!! We still haven't found a reply to this problem. So I was looking to use a "normal" input. Have you got the same problem? Or have some suggestions? Thanks I understand you want to gather the rpm value from an input generating pulses at a relatively high rate. Maybe you could convert the pulses to a simple +/-10VDC analog signal using an external signal conditioner, and simply have the plc scale the analog signal using a strobe or tach or other speed measuring standard for reference. My experience with plc HSCs varying greatly is when the pulses come in at the low end of the speed range, the cycle time variation is going to influence the accuracy of the calculated speed. If your code is using a HSC input count and reading it directly (using HSC_1_tagname:P) with a periodic OB that runs say every 2 ms, you can calculate with a fair degree of accuracy, but you can still only report it at the PLC scan rate and HMI update rate. If your rpm reading is used for motion control, that is a different issue relative to your posted topic.
	science guy
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7/24/2013 6:37 PM	Rate (1)
William_B Posts: 5225 Rating: (1196)	Friend, Thank you for the feedback. We utilise a multi pointed "star" cam on the axis of a 1350rpm motor running at speeds varied between 20Hz and 100Hz. I have not yet used an S7-1200 but did use S7-200 PLC utilising a high speed counter. The sensor is a metal detecting sensor. There are several things to look at.. 1. Sensor should handle pulse rate 2. Sensor should give positive ON and OFF 3. Target should pass by sensor in repeatable way.. no bending. 4. Do not use sensor with reflector. 5. Some sensors have dead spot near distance 6. Using "inverters" / VSD without filtering may cause false signals on wires. 7. Ensure input filter is set appropriately. Higher filter might be good. 8. Careful how HSC is zeroed. I prefer "internal" method using interrupt input with some logic. Now please see if there are any things on my list that is of value to you. My "crystal ball" let me believe you have cross talk signals on your sensor wire. I would also recommend against optic sensor unless you use sender-receiver packaged in a U-sensor. There is a good chance that it is not alone the PLC to blame. Please grant me your thoughts on this matter. Best wishes. w
William_B Posts: 5225 Rating: (1196)
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