Micro Motion
®
Model D and DT Sensors Instruction Manual 57
Purge Fittings continued
3. Connect the supply of dry, inert gas to the inlet purge connection or
open inlet purge line. Leave the outlet connection open.
• Exercise caution to avoid introducing dirt, moisture, rust, or other
contaminants into the sensor case.
• If the purge gas is heavier than air (such as argon), locate the inlet
lower than the outlet, so the purge gas will displace air from bottom
to top.
• If the purge gas is lighter than air (such as nitrogen), locate the inlet
higher than the outlet, so the purge gas will displace air from top to
bottom.
4. Make sure there is a tight seal between the inlet connection and
sensor case, so air cannot be drawn by suction into the case or purge
line.
5. The purge time is the amount of time required for full exchange of
atmosphere to inert gas. For each sensor size, the purge time is
different. Refer to the table below. If purge lines are being used,
increase the purge time to fill the additional volume of the purge line.
6. Avoid pressurizing the sensor case. At the appropriate time, shut off
the gas supply, then immediately seal the purge outlet and inlet
connections. If pressure inside the case elevates above atmospheric
pressure during operation, the flowmeter density calibration will be
inaccurate.
Time required to purge Model D sensor cases
Sensor model
Purge rate
cubic ft/hr (l/hr)
Time*
minutes
* If purge lines are being used, increase purge time to fill the additional volume.
D25 20 (566) 3
D38 20 (566) 3
D40 20 (566) 3
D65 20 (566) 10
D100 20 (566) 15
D150 20 (566) 15
D300 40 (1132) 30
D600 80 (2264) 60
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