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How do you calibrate an analog sensor

Created by: RossHall at: 7/15/2021 8:44 PM (4 Replies)

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7/15/2021 8:44 PM	Rate (0)
RossHall Posts: 15 Rating: (0)	I am looking for a bit of advice on the correct way to calibrate a pressure transducer. I have it installed and all is working as I wanted it to. I connected my calibrated Druck DPI705 to the same source and there is a difference between the two of 30 units. Which value should I adjust on the attached analog amplifier, the gain or the offset. Any help would be much appreciated as I haven't used pressure transducers before. I'd rather know the correct method before I tinker, I'm sure it is obvious. The pressure transducer is a 2.5 bar Absolute 4-20mA version that I am using for vacuum control. Attachment Analog amplifier.JPG (121 Downloads)
RossHall Posts: 15 Rating: (0)
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7/15/2021 9:05 PM	Rate (1)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 12/1/2023 Posts: 31530 Rating: (3916)	Use two analog amplifier in series.... Attachment Pressure_0BA8.Standard.zip (123 Downloads)

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7/16/2021 12:46 AM	Rate (0)
RossHall Posts: 15 Rating: (0)	Wow. Thank you so much, however I don't understand how those settings in the pre-amplifier will do the 30 unit alteration or any alteration for that matter, I don't understand it, yet. Can you explain more for me please how it all relates?
RossHall Posts: 15 Rating: (0)
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7/16/2021 4:55 AM	Rate (2)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 12/1/2023 Posts: 31530 Rating: (3916)	The A/D converter of an analog input of a LOGO! generally converts the signal (regardless of whether it is 0-10V, 0/4-20mA or PT100/1000) into 0-1000 units. The units are then adapted to the respective measuring range of the encoder with an analog amplifier. With a 4-20mA sensor, the first 200 units (0-200) are already used for the 4 mA, so that only 800 units can be used. This results in: - 1,000 bar to 1,500 bar = difference of 2,500 bar. 2,500 / 800 = 3.125. So the gain factor is 3.125. With the analog amplifier, however, only 2 decimal places are possible for the gain. Therefore LSC rounds up, 3.125 becomes 3.13. This then results in the deviations for minimum, maximum and offset. That's why I use 2 analog amplifiers in series in such cases. The first analog amplifier turns the 800 units into 1000 units. 2.500 / 1000 = 2.5 (gain factor of the second analog amplifier). Now the area has to be corrected: 0.000 to 2.500 bar become -1.000 to 1.500 bar by the offset of -1000.

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7/16/2021 12:56 PM	Rate (0)
RossHall Posts: 15 Rating: (0)	WOW. Thank you for explaining that, I would never have worked that out in a million years. I will however keep this in my Dropbox amongst the other tips and tricks for future use :)
RossHall Posts: 15 Rating: (0)
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