Internet PLC Forum
General => Technical support => Topic started by: dan on April 03, 2006, 07:27:34 AM
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Hi,
Two questions:
1. If I use an analog input from the PLC there is a +\_ 4 reading variation. What about using an I-7017. I will get a stady value?
2. There is any command so I can read all the DM (or blocks of DM) or I need to issue 4000 commands ?
Thank you,
Dan
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The ADC ports apparently divide a 5v level into 1024 bits, and then this is multiplied by 4 (to 4096) for some reason, which is why I think you are getting your +/- 4 variation.
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It is a 10-bit ADC (0 to 1024) but normalized to 12-bit (0-4096), that's why the jump is 4 at a time.
I-7017 is internally 24-bit sigma delta ADC but only upper 16-bit are used, so it will appear more steady because the noisiest part of the results at the LSB end are thrown away.
Are you referring to the serial host link command to read DM? You can use the MODBUS ASCII or OMRON C20H protocol to read multiple registers. Please refer to Chapter 4 of User's Manual for details. Remember that the PLC serial buffer is 256 bytes so there is a limit of how many register can be read each time, so you have to split into multiple commands to read all 4000 DMs.