16.7 AUTO-ZERO FEATURE (FOR ANALOG MASS FLOW CONTROLLERS)
16.7.1 Introduction
Celerity MFCs guarantee a zero drift of less than .6% per year, essentially eliminating the
need for the Auto Zero feature. However it is still offered as an option. The Auto-Zero
feature eliminates zero drift as a contributor to long-term process non-repeatability. It
automatically and continuously re-zeros the MFC between process runs. This reduces the
need for frequent calibration, a procedure which can be both costly and time-consuming.
This feature can identify an MFC which is in need of recalibration or repair, and can be
used as a trigger for a system alarm to the operator prior to a process run. (See Figure
#2)
The Auto-Zero feature eliminates zero drift thus maximizing process repeatability. The
significance of this enhanced repeatability is very dramatic at the low end of the MFC
ranges, as shown in Figure 1, where a ±1% zero variance can result in a ±10% error at
10% of full scale.
Figure 1. Zero Variance of +/- 1% the effects
*An alarm may be triggered to indicate that the calibration of this MFC should be evaluated.
28
100%
50%
10%
0%
10% 50% 100%
+10%
-10%
+2%
-2%
+1%
-1%
VOLTAGE
OUTPUT
GAS FLOW
©2005 Celerity
, Inc.
#199-001-0006 REV
.F 4/05
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
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