PN 305200901, Rev YT
Monitoring the Zero Delta Frequency will help you to determine the health
of the Dryers. The Dryers dry the Reference gas during normal operation and
during the Zero calibration, the Sample gas. Hence the reason for two Dry-
ers: one is used in the Reference path (normal operation), the other for drying
the Sample gas during the Zero (Zero Dryer). Dryers do not have an innite
life. Their life time depends on the dryness of the Sample gas and the precau-
tions that should be taken while installing them. If during the installation of a
new Dryer, the technician replacing the device removes the caps that protects
the Dryer from ambient air moisture (H
2
O) and does not install the Dryer fast
enough or leaves the unprotected ends of the Dryer exposed to ambient air
too long (more than three minutes), the Dryer’s life will be shortened. Dryers
act like a sponge. They have a great ability to absorb water (H
2
O), but like a
sponge, at some point they will stop absorbing water due to saturation.
When a Dryer becomes saturated, it no longer removes water (H
2
O) from
the gas, it simply passes it on to the detector. As the normal Reference Dryer
begins to get more wet (saturated), the Zero Delta Frequency value will begin
to drift negatively (increase in the negative direction). Conversely, as the Zero
Dryer begins to get more wet (saturated), the Zero Delta Frequency will begin
to drift positively (increase in the positive direction). The reason is because we
measure wet Sample versus dry Reference gas (refer to the “Overview” section
– Chapter 1 of this manual – for more information about the QCM).
In ideal conditions, if the Reference (dry) gas stream were always perfectly dry
and never deviating from 0.000 PPMV of moisture (H
2
O), the Zero Delta Fre-
quency would always be a positive number. But, since it depends on the qual-
ity of the Dryers, it will drift in either direction (positive or negative).
As stated earlier, the Zero Delta Frequency is limited by the value assigned
to the variable ID Number 86 Hex (MaxZeroError). The default value for this
parameter is 0.5 Hz.
This means that when the Zero Delta Frequency exceeds this limit, a Zero Error
message will be displayed and no Zero adjustment will take place. This error
message cannot be cleared until a successful Zero is accomplished. You can
obtain a good Zero by increasing this limit and running another Zero. By doing
this, you will bring the analyzer back on line (eliminate the alarm), but you will
have to replace the defective Dryer as soon as possible.
4-20 | 3050-OLV Moisture Analyzer
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