What is the need for DP transmitter in boiler
Boilers have both forced draft and induced draft.
Forced draft flow FD can be DP type /flow nozzle for inlet burner air.
Induced Draft, ID uses DP type for Flow towards the stack.
Low-pressure variations as it is atmospheric, DP type is most sensitive, and easy maintenance is possible.
Most manufacturers do not have a very low pressure, ‘draft range’ gauge pressure transmitter because of low market demand for such. In fact, I do not know of a manufacturer of industrial ‘draft range’ gauge pressure transmitters.
So the when a low pressure ‘draft range’ pressure transmitter is required, the only model available for ‘draft range’ is a ‘draft range’ DP differential transmitter.
With a DP transmitter the high side port is the same as gauge pressure sensing port. The low side port on a DP is left open to atmosphere, although I always install a mesh or sintered filter in the low side port to prevent insects from building homes in the low side sensing area.