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DMM Shield multiplication factors


Question

I have been playing with the Digilent DMM shield and trying to understand how the shield and the ic hy3131 work. My question is about the multiplication factors which are used for converting the adc value to real value.

For example, the multiplication factor in the library for 5V DC range is125e-1/1.8/8388608

If I'm correct, in 5V DC range the input signal is divided by 10 and fed into the adc whose reference voltage is 1.2V, so my question is why we multiply the value by 12.5? Shouldn't it be 12.0 instead because the reference voltage is 1.2V?

 

Edited by itlki
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Hi @itlki,

Welcome to the Digilent Forums!

We have reached out to an engineer more experienced with the DMM Shield.

While we are waiting for their input

Here is the DMM Shield's resource center.

Which library are you referring to?

Arduino DMM Shield Library User Guide

PIC32 DMM Shield Library User Guide

Zynq DMM Shield Library User Guide

Can you be more specific where in the library your concern is?

best regards,

Jon

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Thanks @jpeyron

I'm referring to the Arduino DMM Shield Library. In the library, there is a file called "dmm.cpp" which contains the configurations of the dmm IC (hy3131). Each configuration (called DMMCFG) has a field called multiplication factor. 

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Hello,

As you noticed, this multiplication factor applies to the value acquired from AD converter. It encapsulates the converter gain, the converter maximum value (2 ^ 24) and a scale factor. This factor should be considered as a whole.

After applying this multiplication factor, the acquired values are corrected using the two calibration factors (additive and multiplicative).

 

 

Edited by Cristian.Fatu
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