INA333: ground connecting issue with differential amplifiers

Tomasz Siuchninski

Part Number: INA333

Tool/software:

Hello, I would like to ask about the possibility of using the INA333 for measuring current in a 4-20 mA loop, and the related issue of connecting the grounds of the devices. Do I need to connect the grounds, or is the circuit capable of measuring the voltage across a resistor without linking the grounds of both devices? Thank you in advance for your help.

7 months ago

0 Clemens Ladisch 7 months ago

Guru 318300 points

Are you using a two-wire or three-wire loop? Please show a schematic.

0 Tomasz Siuchninski 7 months ago in reply to Clemens Ladisch

Prodigy 10 points

0 Clemens Ladisch 7 months ago in reply to Tomasz Siuchninski

Guru 318300 points

According to this schematic, the inputs are not connected to anything.

Please show the complete schematic, including the transmitter.

0 Tomasz Siuchninski 7 months ago in reply to Clemens Ladisch

Prodigy 10 points

That's the point, I'd like to be connected with industrial 4-20mA standard with some device that i don't know

0 Clemens Ladisch 7 months ago in reply to Tomasz Siuchninski

Guru 318300 points

There are multiple standards. In a two-wire system, the transmitter is supplied through the loop and has a floating ground. In a three-wire system, the transmitter has three connections, power, output, and ground.

Your circuit should have one input, and connect the other end of the measurement resistor to its own ground.

0 Tomasz Siuchninski 7 months ago in reply to Clemens Ladisch

Prodigy 10 points

Okay, I will ask question another way. I connect battery to VIN- and VIN+ of INA333 or similar (battery is not connected to ground of ina333), will it measure its voltage properly?

0 Clemens Ladisch 7 months ago in reply to Tomasz Siuchninski

Guru 318300 points

The INA333's common-mode range is between its supplies, so a floating battery can be measured this way.

(With both two-wire and three-wire systems, the transmitter has only one output, so you must connect VIN− to ground yourself.)

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INA333: ground connecting issue with differential amplifiers