DRV421: Residual current detector application. (Regarding the fluxgate sensor front-end offset)

Roberto Rico

Part Number: DRV421

Hello,

We are trying to develop a current transducer for residual current detection (RCD) and are looking into using the DRV241 in our design. The client needs to measure a range between -200 and +200 mA and a fault detection of 5 mA.

Reviewing the datasheet and the system parameter calculation available in the product page, we noted that the fluxgate sensor front-end offset would be the main issue for this application.

Is this offset specific for each IC or does it change over time? Would it be possible to calibrate the reading at the ADC during the assembly to reduce its effect?

Thank you.

Roberto

over 3 years ago

0 Javier Contreras4 over 3 years ago

TI__Mastermind 28250 points

Hello Roberto,

RCD will be a challenge with this device. The offset will change slightly over time but your core may have a bigger change than the DRV421. External field will also impact your measurements. Also how close your current carrying conductors are to the air gap will impact your measurement as they can couple through the air gap rather than through the core..

Please take a look at these post as well.

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/727789/drv421-technote-rcd-leakage-module-using-the-drv421

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/941265/drv421-doubts-and-questions-regarding-feasibility-of-rcd-residual-current-detector-design-with-drv421-ic

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/871614/drv421-residual-current-measurement-in-ac-distribution-system-1phase-or-3phase

Also with a higher Rshunt you will have issues with the degauss function. I would look at driving my own degauss function.

0 Roberto Rico over 3 years ago in reply to Javier Contreras4

Prodigy 20 points

Hello Javier,

Thank you for the feedback. We will run some simulations to get some numbers specific for our application.

0 Roberto Rico over 3 years ago in reply to Javier Contreras4

Prodigy 20 points

Hello Javier,

We've been working on the coil design of our sensor. But, we are currently struggling to reach the inductance above 100 mH required to avoid stability issues according to document "Designing With the DRV421: Control Loop Stability".

According to the equation above from the cited document, the corner frequency is determined by the parasitic resistance of the coil, the shunt resistance and the inductance. Is it possible to reduce this frequency by adding an in-series inductance with the sensing coil?

Thank you!

0 Javier Contreras4 over 3 years ago in reply to Roberto Rico

TI__Mastermind 28250 points

Hello Roberto,

You could as this stability issue and in the core or not it still sees the inductance in the loop. As the compensation drive attempts compensate the impedance that is sees is what causes the pole as seen in the "Designing with the DRV421: Control Loop Stability".

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DRV421: Residual current detector application. (Regarding the fluxgate sensor front-end offset)