Background; Procedure - Ametek 5000 Instrument Manual

DETERMINATION OF OFFSET AND COEFFICIENT

Background

Because sample and reference gases travel different paths to the analyzer cell, they are subject-
ed to different outgassing effects. The components they pass through outgas at constant but
dissimilar rates. This results in a different amount of moisture being sorbed by the sample and
reference gases and creates an offset frequency between the two gases. For low moisture con-
centration applications (< 1 ppm), this zero offset must be eliminated from the measured cell
Dfrequency which is used to determine the moisture content of the sample gas. The correc-
tion is done by introducing the offset frequency, also known as coefficient D, into the moisture
calculations. The following procedure is used to determine the values of coefficient D for each
sample point (PolyCoef_DX where X = sample point 1 4).
This procedure may take over 2 hours to complete for four-point operation. Arrangements

must be made for the analyzer to be off-line for the duration.
NOTE

Procedure

t 1) l For systems using conditioned sample gas as reference, the reference gas will be used
as the sample input for this procedure. To do this, configure the dry reference bypass
loop as shown in Figure C1. Close the sample shutoff valve and open the dry reference
bypass valve. Some of the conditioned reference gas will be diverted to the sample
input.
OR
l For systems using separate gas source as reference, the sample must pass through
similar conditioning components. To do this, configure the dry sample bypass loop
as shown in Figure C2. Note that only a molecular sieve dryer is shown in the loop; if
other components (super-activated dryer, trap) are used, these must also be in the loop.
Adjust the three-way dry sample bypass valves as required to divert sample through
the loop before the sample input.
2) Verify that both sample and reference flow rates at the field unit are the same. Adjust the
appropriate field unit pressure regulator as required.
3) Configure the software for this procedure; note that the Level 3 access code will be re-
quired.
a. Refer to page 4-2: Display Flags to view the current values of Line_2_Flag and Line_3
D ADJUSTMENT
Coefficient D Adjustment C-1