Chapter 3: Installation
25
Note
Zeroing should be done only on units that are installed in final position.
It is recommended to completely
stop the gas flow prior to any zero
adjustment.
If a pressure difference exists at the mass flow control unit then a small
flow might occur even if the integrated control valve is closed. This is
more likely with special units for low inlet pressures.
Do not adjust the flow signal then to zero because it is a real flow but
use a positive shutoff valve to definitely stop the flow.
The integrated control valve may not completely shut off the gas flow.
3. Periodically check the zero adjustment of the unit, e.g. on maintenance intervals. The zero
adjustment is mainly affected by thermal effects and especially by contamination.
Beside the need for achieving measurements of highest accuracy the zero signal is a very
important indication for diagnosing the condition of flow sensor and control valve.
Zero Button
Figure 8 Zero Button
Zero Button
As long as the Zero Button is pushed, the SI LED will blink each second:
• 1-2 sec = ZERO function is triggered if the actual flow is smaller than 5% of full scale and
the control valve is closed
• 5 sec = reset of device (reset is equal to a power cycle)
• 7 sec = switch USB mode from MSD to CDC or vice versa (for details see chapter
Chapter 4: USB Setup Interface page 27)
To Next Page
Loading...
