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The objectives of the following procedure is to
establish the setting of phase which will align the
phase control circuit with the product signal. The
correct setting will give minimum signal from the
product on the bargraph display.
There will be one value of phase which will give the
minimum signal, this is known as the "null point"
setting. Changing the phase setting up or down in
value from this setting will increase the amplitude of
the signal.
It is much easier to find the correct phase setting by
starting at a low sensitivity setting then repeating the
process in stages at increasing sensitivities.
When using the phase control to minimise product
signals the detector may become more susceptible to
vibration. The final setting of the sensitivity may be
limited by vibration effects rather than product effect.
1)
Ensure product is flowing through the detector
creating worst case product effect conditions,
refer to 'Notes On Passing A Product Through
The Detector' earlier.
2)
Enter Supervisor/Engineer access code, page 19.
3)
Select lowest available product number (01 to 20)
, page 40.
4)
Set the 'Operating Frequency' to HIGH (default
setting), page 41.
5)
Set the 'Power drive' to HIGH (default setting),
page 41.
6)
Adjust the sensitivity so that the peak signal from
the product gives 3 to 4 bars on the LED
bargraph display. If the signal is very large, such
that the sensitivity control falls below a setting of
100 refer to note (1).
7)
Press the 'Enter' key to store the new setting in
memory.
8)
Set phase to 000.00°.
9)
Adjust sensitivity so that the peak signal from the
product gives just less than full scale indication
on the LED bargraph display.
4618 - 021
OPERATING INSTRUCTIONS
10) To find the null point, change the phase setting to
10° and observe if the amplitude of product
signal indicated on the bargraph display reduces.
Repeat the process increasing the phase setting
in steps of 10°, i.e. 20°, 30°, 40°, 50°, 60°, etc.
until the null point is located.
For example if as the phase setting is increased
there is clear reduction in signal from 80° to 90°,
and then from 90° to 100° the signal starts to
increase again, this indicates that the null point is
between 80° and 100°.
11) Now reduce the phase setting in steps of 2° i.e.
98°, 96°, 94°, 92°, etc. the product signal
indicated on the bargraph display should now
reduce in amplitude. Decrease the phase setting
in steps of 2° until the product effect signal is
reduced to a minimum and then starts to
increase again.
For example if as the phase setting is reduced
there is clear reduction in signal from 94° to 92°,
and then from 92° to 90° the signal starts to
increase again, this indicates that the null point is
between 94° and 90°.
12) At this stage the product effect signal indicated
on the bargraph display should be quite small.
To obtain a more precise phase setting increase
the sensitivity setting to give a larger signal
indication on the bargraph display.
13) Now increase the phase setting in steps of 0.5°
i.e. 90.5°, 91°, 91.5°, 92°, etc. until the product
effect signal is reduced to a minimum and then
just starts to increase again. Using the 0.1° digit
adjust the phase setting up and down until
minimum signal i.e. the null point is found.
14) Although not always necessary a more precise
null point will be found by now using the 0.01° in
a similar manner to the 0.1° digit as described in
13). Using the 0.01° digit adjust the phase
setting up and down until minimum signal i.e. the
null point is found.
The phase control circuit is now aligned to the
product signal, next adjust the sensitivity so that
the product signal gives a maximum signal of 3 to
4 green bars on bargraph display. If the
sensitivity setting is less than 100 refer to note 1).
15) Check the susceptibility of the detector to
vibration, if unacceptable (i.e. system vibration is
showing on the bargraph) reduce the sensitivity
until acceptable.
29
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