Following on from Jims comment, purges lines have been used for a long time. But I note that only continious purge and capilary systems have been mentioned.
Continiously purged impulse lines are useful especially in gas measuring, or liquid level allplications(bubbler).
Remote seals on dp transmitters are another useful solution. but I agree that ambient effects can be an issue especially where they are fitted by third parties to standard transmitters. A good solution for this is to use a transmitter designed with factory fitted capilaries. These can be designed to have greatly reduced volume of fill volume. The less liquid there is in the fill, the less it is effected by temperature.
So the missing link in this thread for me were intermittant purge systems. These are useful to solve the problem posed. By connecting a water solenoid valve that is controlled by a timer, it is possible to flush the impulse lines periodically.
The effect on the transmitter calibration can be seen before and after the purge. A word of caution the DP transmitter should be capable of taking the full purge pressure on one side of the DP measurement with damage. This is not too big an ask from a quality manufacturer.
The great benefit in this solution is that you can minimise the water being injected into the process and adjust the frequency and duration of the purge to suit the application.
I have used this many times on flue gas flow metering.
ione thing that is not mentioned inthis thread is the differen
I trust this helps,