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S7 -1200 SM, 1234 AI/AO

Created by: Dr. K. Khandakji at: 3/2/2012 2:21 PM (4 Replies)

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3/2/2012 2:21 PM	Rate (0)
Dr. K. Khandakji Posts: 2 Rating: (0)	Dear Sirs, I am creating a control system where PLC S7-1200 with SM 1234 AI/AO is used, I have the following questions: 1. Can I apply an ac, 60Hz singnal (Voltage: 1V rms)on one of the Analog Inputs terminals, and between which terminals the connection should be? 2. Will the ac voltage be converted to its equivalent weight of (+27648 to -27648) so that it can be mathematically treated. 3. Can the RMS or the MAX value of the ac voltage applied on the terminals of the analog input be calculated using the math blocks or any other means so that it will be used somewhere in the ladder? Best Regards, K. Khandakji
Dr. K. Khandakji Posts: 2 Rating: (0)
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3/2/2012 3:01 PM	Rate (0)
LarryAm Silver Member Joined: 9/19/2011 Last visit: 11/11/2024 Posts: 140 Rating: (33)	Hello Dr. K. Khandakji, How fast do you need the value of the input?The S7-1200 PLC CPU only scans the inputs every scan. The fastest scan is 1ms. This means that the PLC will only read 16 samples per cycle of the input. If this data is evaluated for an extended time period, say 1 second, then the maximum and minimum can be determined for this time period and the value (MAX and RMS) can then be calculated. The Noise reduction (integration time) must be set to 400Hz (2.5ms) to pass the 60 Hz input signal. Best Regards, Larry PS: You should upgrade you PLC CPU firmware and TIA software to the latest versions which are V02.02.00 and V11 SP2.

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3/2/2012 6:33 PM	Rate (0)
Dr. K. Khandakji Posts: 2 Rating: (0)	Dear Mr. Larry, Thank you for your quick reply. When I tried to apply (-9V dc) on the analog input of SM1234, I read in the PLC ladder a number that wasabout 49768 which is almost double the weight of (+9V, i.e. 2 x 24885= 49786), why I did not get (-24885)?? I am using TIA V10.5. Should I make some changes in the software or in the hardware connection before applying negative signal on the analog input? Advise please. Regards, K.Khandakji
Dr. K. Khandakji Posts: 2 Rating: (0)
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3/2/2012 7:47 PM	Rate (0)
LarryAm Silver Member Joined: 9/19/2011 Last visit: 11/11/2024 Posts: 140 Rating: (33)	If you are using a watch table be sure to use DEC_signed and not DEC_unsigned. Larry

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3/2/2012 7:50 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/15/2024 Posts: 15402 Rating: (2444)	How have you configured the analog input module's inputs? From the specifications for that module: SIMATIC S7-1200, ANALOG I/O SM 1234, 4 AI / 2 AO, +/-10V, 14 BIT RESOLUTION, OR 0-20 MA, 13 BIT RESOLUTION If you are using it with +/-10V configuration, the resolution is 14 bits -higher than the values for 12-bit analog (like on the PLC built-in analog inputs). Do you have the under/over flowdiagnostics checkboxes checked or unchecked? What about the AI channel setup? +/-10VDC? What about the wiring for L+/M/GND ? The range should be -27648 to 27648. If you set up the input word as UINT instead of INT, then the value 49768 => 6.15VDC. Is that what you measured at the analog input module terminals? Attachment SM1234_Wiring.jpg (439 Downloads)
	science guy
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