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SM1231 AI floating zero

Created by: Swarkandy2 at: 2/3/2011 10:29 PM (3 Replies)

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2/3/2011 10:29 PM	Rate (0)
Swarkandy2 Posts: 2 Rating: (0)	Hello All, working with an 1212C and SM1231 4*AI. Measuring a 0mV to 4.5 Volt Signal. Applied scaling and norm and it works just fine most of the time. Only when the signal is at 0mV occasional my reading goes sky high. The voltage is generated by an process calibrator. So it is dead stable. Checked in my program online and noticed that the HDW signal sometimes goes up to 6533 instead of the expected 0 value. I have shortened the particular input , no change. Since only using one input , shorted the others as well. No change. How do I make sure the signal remains at 0 when a true 0mV is applied. regs, Andy
Swarkandy2 Posts: 2 Rating: (0)
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2/3/2011 10:36 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/15/2024 Posts: 15402 Rating: (2444)	Most likely your signal is detecting as slightly negative which puts into a state that numerically appears high. You can copy the value from the AI to a working memory tag, and then if it goes above the 20 mA threshold, you can detect whether the last value was near 0 or near 20 mA and either set it to 0 or at 20 mA. If you can change it to read +/- 20mA, that reduces your accuracy, but does get rid of the problem. There are a few FAQs and posts related to scaling and handling out of range problems. If you have an offset in your input calibration, perhaps calibrate it to send 4-20 mA for 0-maxinstead of 0-20 mA. Then you never see negative values.
	science guy
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2/4/2011 1:51 PM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	try using signal conditioner and signal filter. Have luck.
	Aim Higher
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2/4/2011 2:24 PM	Rate (0)
Swarkandy2 Posts: 2 Rating: (0)	Hello , in the field a signal conditioner with build in filter is present. The problem described was when using a process calibrator while sitting at my desk. At any rate , I fail to understand a shorted input yields a negative value. (and this just at random). I have set up my signal conditioner to have a live zero , so I do not have the issue anymore. thank you for your help. Andy
Swarkandy2 Posts: 2 Rating: (0)
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