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LOGO! 8 Analog Inputs at low volts.

Created by: Paulio at: 11/27/2019 9:31 PM (11 Replies)

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11/27/2019 9:31 PM	Rate (0)
Paulio Regular Member Joined: 6/26/2019 Last visit: 3/10/2020 Posts: 5 Rating: (0)	Hello everyone, Im hoping for some advice. I have a LOGO8 12/24v unit and I have been using the analog input options. I have found that when the voltage drops below around 0.3 volts the readings become unstable and start to jump around. I have discovered this whilst trying to use LM35 sensors but have also tested with a voltage signal generator which holds a stable reading until <0.3 volts again. Is the LOGO able to read mV at a low level reading?

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11/27/2019 9:44 PM	Rate (2)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 7/7/2022 Posts: 27286 Rating: (3309)	Hello Paulio, at first welcome to the forum. The analog inputs of the basic module of the LOGO! have a fault tolerance of 1.5%. This means that ±0.15 V can be evaluated as an error. With a measuring range of 0.0 - 10.0 V the error in the range of 0.3 V is of course very high. Temperature sensors such as the LM35 are unsuitable for accurate measurements.

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This contribution was helpful to 2 thankful Users Paulio RKBIS

11/27/2019 11:20 PM	Rate (0)
Paulio Regular Member Joined: 6/26/2019 Last visit: 3/10/2020 Posts: 5 Rating: (0)	Thank you for your help.

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11/28/2019 6:19 AM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 7/7/2022 Posts: 27286 Rating: (3309)	Hello Paulio, you're welcome....

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12/4/2019 9:52 AM	Rate (0)
Roldy Experienced Member Joined: 8/23/2010 Last visit: 6/13/2022 Posts: 3 Rating: (0)	This defect has been eliminated since the date of manufacture 8/2019.

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12/4/2019 9:56 AM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 7/7/2022 Posts: 27286 Rating: (3309)	Roldy This defect has been eliminated since the date of manufacture 8/2019. From what defect speak you?

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12/4/2019 10:01 AM	Rate (0)
Paulio Regular Member Joined: 6/26/2019 Last visit: 3/10/2020 Posts: 5 Rating: (0)	The unit I use is dated 11.2018 FW V1.82.01. The reading of the mV seems ok higher up but not at low range.
	Last edited by: Paulio at: 12/04/2019 10:03:18
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12/4/2019 10:05 AM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 7/7/2022 Posts: 27286 Rating: (3309)	There is an firmware update available (V1.82.02). LOGO! Soft Comfort V8.2 SP1 (download, notes, instructions)

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12/4/2019 6:57 PM	Rate (0)
Paulio Regular Member Joined: 6/26/2019 Last visit: 3/10/2020 Posts: 5 Rating: (0)	Thanks for the link, unfortunately this made no difference to the input capabilities. above 0.30v the input can accurately read in 0.01 increments. Bellow that it does not have the capability to read accurately which is a shame. ixo65 There is an firmware update available (V1.82.02). LOGO! Soft Comfort V8.2 SP1 (download, notes, instructions)

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12/4/2019 7:09 PM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 7/7/2022 Posts: 27286 Rating: (3309)	That was not the reason why I recommended you the update. It is just a fact that the error in the lower range of 0-10V has a heavier impact than the upper range. And so my statement that the evaluation of sensors such as the LM35 is not suitable with the LOGO!, if accurate results are expected.

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