As with all purged systems, certain criteria must be met for successful operation. Listed here
are some of them:
• The purge gas supply must be reliable: if the flow stops for any reason, the level measurement
will cease to be accurate, and the dip tube may even plug with debris!
• The purge gas supply pressure must exceed the hydrostatic pressure at all times, or else the
level measurement range will fall below the actual liquid level.
• The purge gas flow must be maintained at a low rate, to avoid pressure drop errors (i.e. excess
pressure measured due to friction of the purge gas through the tube).
• The purge gas must not adversely react with the process.
• The purge gas must not contaminate the process.
• The purge gas must be reasonable in cost, since it will be continuously consumed over time.