DRV425EVM: Reducing noise at high frequencies for far field current detection

Noah Perkovich

Part Number: DRV425EVM

Tool/software:

Hello, I am working on a project to sense current in power transmission lines at distances of roughly 10m. I have the DRV425EVM and a high speed ADS. I expect the anomalous field intensity to vary between a few nT to a few hundred nT due to load imbalance in the transmission lines. I need to capture the 60Hz waveform and want to sample faster than 1kHz.

The EVM comes with a 100 ohm resistor, and the user manual suggests that increasing this will increase sensitivity and decrease max field. Will it also reduce noise density?

Also the datasheet for the senor itself quotes a 1.5/root(Hz) noise density. It is unclear if that is what I should expect using the EVM as it is factory configured. If not could you please explain what I should expect with factory EVM and what i could expect by changing the R1 resistor?

Thank you,

Noah

5 months ago

0 Javier Contreras4 5 months ago

TI__Mastermind 30790 points

Hello Noah,

Noah Perkovich said:
The EVM comes with a 100 ohm resistor, and the user manual suggests that increasing this will increase sensitivity and decrease max field. Will it also reduce noise density?

Unfortunately the noise is from the input side of the flux-gate so the noise will not change.

Slowing down the signal at the output will help (bandwidth limit) but it depends what you are attempting to measure. Please see if these post help: https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/976335/drv425-noise-analysis

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/967745/drv425-precision-measurements-of-earth-s-magnetic-field

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1032637/drv425-constant-vout

Noah Perkovich said:
If not could you please explain what I should expect with factory EVM and what i could expect by changing the R1 resistor?

By changing R1 you change the range that you are able to measure. Even if you are attempting to measure low field and you change the range to +/- 10µT range if you have DC field like from the earth then you would need to account for that as it would saturate your sensor depending on orientation. You would still need to filter if you would like lower noise.

0 Noah Perkovich 5 months ago in reply to Javier Contreras4

Prodigy 10 points

Hi Javier,

Thank you for the prompt response.

Can the bandwidth be configured to any frequency, or is is limited to 47kHz or 32kHz?

Best,

Noah

0 Javier Contreras4 5 months ago in reply to Noah Perkovich

TI__Mastermind 30790 points

Hello Noah,

You can place a filter at the output to get less noise and limit the output bandwidth you see. The internal frequency of the compensation is not adjustable other than the configuration you mentioned.

Regards,

Javier

0 Noah Perkovich 5 months ago in reply to Javier Contreras4

Prodigy 10 points

Hi Javier,

Yes I am using RC filters for my desired band. Will noise within my desired band be reduced at all by configuring it to 32kHz? If so, what do I need to change on the EVM board to do so?

Thank You,

Noah

0 Javier Contreras4 5 months ago in reply to Noah Perkovich

TI__Mastermind 30790 points

Noah,

It may help but I don't know how much as the frequency of the flux-gate will not change much. To experiment this please make BSEL = 0. This can be done by uninstalling R3 and installing a zero ohm in R4. Note you cannot have R3 and R4 installed at same time as this will create a short from VDD and supply.

0 Noah Perkovich 5 months ago in reply to Javier Contreras4

Prodigy 10 points

Javier,

Thank you for the help, I will give it a shot this week.

Best,

Noah

Sensors

Sensors forum

DRV425EVM: Reducing noise at high frequencies for far field current detection