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I'm designing part of an application that will consist of an Omron D6F-P0010A1 MEMS flow sensor. The analog output of the sensor will be connected to a TI ADS1114 ADC.

I'm trying to figure out from the respective datasheets whether I'm going to need a buffer in front of the ADC or not.

The datasheet for the Omron sensor doesn't mention source impedance anywhere, only that its charts were measured at a load resistance of 10k. The datasheet for the ADC specifies common-mode/differential input impedances of 3M and 2.4M at the scale I am likely to use.

I'd like to get accurate readings from the sensor, so do you think that a buffer will be necessary?

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  • \$\begingroup\$ Omron link appears to be broken for me. What's the distance between the sensor and ADC? Powered separately, or same supplies? Hot plugged? \$\endgroup\$ – Chris Knudsen Sep 12 '18 at 19:20
  • \$\begingroup\$ Sorry about the link - probably a digikey regional redirect. Fixed with direct link to DS. The devices will be powered from the same supply. Fixed and not hot plugged. Distance between sensor output pins and ADC less than 10cm. \$\endgroup\$ – Andy Brown Sep 12 '18 at 19:34
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According to the datasheet the output is specified with a load of 10K\$\Omega\$.

That implies a relatively low source resistance, probably well under 500 ohms, given the +-5% accuracy specification.

Most microcontroller ADCs are quite happy with a few k\$\Omega\$ source impedance. The chip you are intending to use is even more forgiving, if you look at the differential and common mode input impedances.

Of course if you want to add signal conditioning such as low-pass filtering you may want a buffer, but chances are that's already built into the sensor.

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  • \$\begingroup\$ That sounds promising though I'm not going to use the built in micro ADC (it's the ESP32) because it seems to have (or has had) issues with linearity and noise. The TI ADS1114 also has a programmable gain that I want to take advantage of to focus on the range of gas flow rates that I expect to receive. \$\endgroup\$ – Andy Brown Sep 12 '18 at 19:41
  • \$\begingroup\$ The input impedance is quite high in comparison to 10K, so I think it's fine (see the numbers at the top of Page 7 of the datasheet). \$\endgroup\$ – Spehro Pefhany Sep 12 '18 at 19:46

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