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Hello ,

Need some help.

I have NTC sensor 10k Ohm at 25 C , connected through the voltage divider to Jazz 10-11-ua24 analog 0-10V input.  When divider is not connected to plc , and i measure voltage between R1 and ground it shows 5 V , and then i connect it to the plc , voltage drops to 4V.

What is the reason ?

i have made a drawing of connection diagram

Bagel NTC calibration.spl7.pdfAleksei

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• MVP 2023

You're adding a resistor in parallel to R1 when you connect the analog input; the spec lists 20K ohms as the input impedance.  The effective resistance (Re) below the sensor will be 6.67K.

Applying the voltage divider formula Vr = Vs*Re/ (Re + Rs) = 10 * (6.67) / (6.67 + 10) = 4.00

You're going to have to re-size R1 to compensate for the input impedance of the module.  I'll leave that as an exercise for you.  Or you could just adjust your scaling logic.

Joe T.

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You're adding a resistor in parallel to R1 when you connect the analog input; the spec lists 20K ohms as the input impedance.  The effective resistance (Re) below the sensor will be 6.67K.

Applying the voltage divider formula Vr = Vs*Re/ (Re + Rs) = 10 * (6.67) / (6.67 + 10) = 4.00

You're going to have to re-size R1 to compensate for the input impedance of the module.  I'll leave that as an exercise for you.  Or you could just adjust your scaling logic.

Joe T.

Thanks for the fast response.

Cheers

Aleksei Bagel

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