Malvern Instruments Spraytec, User Manual

Page: 161 / 221

Background alarms
Background alarms are used to alert the user of errors if the background signal at
the start of the measurement is too high. A background measurement has two
components:
.
Electrical background measurement – measures only the amount of
electrical noise generated by the instrument and background light; a laser
shutter moves in front of the laser during this measurement to block all la-
ser light.
.
Optical background measurement – measures the environment the mea-
surement will be performed in. It is a measurement of the cleanliness of the
optics and the dispersing environment (the air) around the instrument.
An alarm can be raised if:
.
An electrical background measurement finds the electrical background
noise is too high or detects too much ambient light. In this case an
elec-
tronic background alarm is raised.
.
An optical background measurement detects a high background; in this case
an
optical background alarm is raised.
A high optical background may be present if:
.
The transmission (laser beam power) is too low.
.
The optics are dirty – this will cause light scattering on the detectors.
.
The instrument is poorly aligned.
'
N o t e
. During a manual measurement the background screen can be displayed
for the user to make a judgment on the cleanliness of the system.
Setting background alarms
The Background alarms SOP wizard dialogue is shown below. Set the warning
threshold in the first column and the error threshold in the second column.
C H A P T E R 1 0
S p r a y t e c
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