Honeywell ACM 150 Manual To Installation, Operation, And Maintenance page 124

ACM 150
Signal-to-noise ratio (S/N)
Follow the instructions in
past 15 days of the 'Background S/N Ratio'. Expect S/N to degrade slightly and
trend downward over time. If there is a sudden drop in S/N or if the value falls below
acceptable limits, it fails this evaluation.
Spectral balance
Follow the instructions in
this Background Spectrum by comparing it to the reference diagrams in
resolving spectral
20% of the signal intensity at 2000 cm
your Background Spectrum. If the spectral balance is inadequate or if the spectrum
shows a dip or other pattern that deviates from normal, it fails this evaluation.
Determining the next step
The next step is determined by the results of the preceding three evaluations, and
the choices are:
1. If these evaluations do not fail and if you have no other problems, e.g. related
Service Status messages, there is no need to clean the gas cell, and there is no
need to adjust the gain or optimize the optical alignment.You can proceed to
Servicing the line leak
2. If the ACM 150 monitor failed one or more evaluations and/or if you have other
problems, e.g. related Service Status messages, proceed to
cell (unless the problem is a ZPD value that is too high).
Servicing the gas cell
Service objective
The objective when servicing the gas cell is to correct any conditions which
significantly reduce the infrared signal passing trough it. The 5 meter long path gas
cell also requires clean and clear windows, but it has the added complication of
internal mirrors at both ends as well as external mirrors (or "transfer optics"). (The
Perkin Elmer bench has all optics sealed away from service personnel.) The external
mirrors must be clean and highly reflective. So, conditions which foul the windows
should be avoided or controlled in the sample system design.
Lengthening the service interval
In previous generations of the ACM product line, the long path gas cell was
mounted vertically. In this orientation, particles and condensable vapors would
often accumulate at the bottom of the cell on the internal mirrors and the gas
cell windows. The ACM 150 monitor is designed differently with the gas cell in a
horizontal orientation. The low point for collecting particles and condensable vapors
is the inside of the glass housing, which is not in the infrared path. This design
results in less frequent servicing of the gas cell. Also, if you always have in-line filters
installed on all of the sample lines, the gas cell filter provides a second stage of
filtration. Two-stage filtration minimizes particle accumulation in the gas cell.
Background, S/N and drift
Acquire background. Evaluate the 'spectral balance' of
balance. Verify that the signal intensity at 4000 cm
. Look for any anomalies in the pattern of
-1
test.
and look at the trend over the
124
Evaluating/
is at least
-1
Servicing the gas