Identifying an exhaust fan inlet component

[Haotranphotomask]

Hello, I need some help determining what this piece of equipment is. It is currently attached to the inlet of my exhaust fan and controlled by some electrical signal. I am thinking it may be a pressure relief damper, but not sure if I am correct. I could not find any nameplate/set point for the piece. Could you guys please help?

 

[Lnewqban]

It seems that you have a similar thing installed for the other fan.

It should be an automatic damper to incorporate some fresh air into the airstream that is exhausted from the building.
It could be a mean to dilute toxic or bio-hazardous gases prior to release those upwards into the atmosphere.

The screen is just to prevent birds from nesting inside that intake.

Please, see:
https://www.greenheck.com/products/air-movement/fans/laboratory-exhaust-fans

If the motor of the fan is constant velocity, that automatic damper could also have a by-pass function, so the static pressure in the exhaust duct and laboratory hoods is kept constant and optimal for lab operation.

Please, see:
https://content.greenheck.com/public/DAMProd/Original/10017/VSC_Comp_Guide.pdf

 

[russ_watters]

It's likely there to maintain a constant 3,000 fpm stack velocity(code required in some cases) despite receiving a variable exhaust volume from the building.