Can we use a DPT (Differential Pressure Transmitter) as a normal PT (pressure transmitter)?

Note that in principle every pressure transmitter measures with reference to atmosferic pressure, except a vacuum transmitter.  However, these transmitters do only have one process connection. A dP transmitter has two process connections, positive and negative, and so capable to measure a dP. The sensing element itself ultimately determines what range can be measured. So depending on the range of the sensing element, often a capacitive type membrane, gauge pressure (reference to atmospheric P) can be measured while the negative process connection is connected (open) to atmosferic pressure.  Note that normal dP sensor elements do have a limited range while a dedicated gauge Pressure transmitter is able to measure much higher ranges than a dP transmitter !

Concluding: Yes it is possible to measure gauge pressure when the refernce is open to atmosphere while one need to consider the range of the sensing elements (specified by the supplier !)

i guess if we made one side for atomosphere and the other for the measured pressure we then are comparing1 bar for what ever u have

If you are measuring high pressure and small variation is not important then you can use it.

Because there will be small variations in the pressure so if you are measuring sensitive pressure it will affect with the atmospheric pressure and the wind speed and direction.

vent the low side to air

yes it is possible butt in this our low side of the transmitter will be open at atmospheric pressure.

This question was asked at a job interview!!