Lock Inspection Systems MET 30+ Operating Manual page 18

Doc. Ref.No: Q875-0143/ENG Issue 2 12/01/10
Met 30+ Operating Manual
When the detector generates a trigger a delay timer is started as for the "no
synchronising photocell" situation. When the delay timer expires an enabling alarm
timer is started. The reject mechanism will only activate while this alarm timer is
active. As each product passes along the belt it breaks the synchronising photocell
beam and generates a photocell pulse. A photocell delay timer is then started. If this
expires and the product was uncontaminated then the alarm timer will not be active
so nothing happens. However if the product was contaminated then, when the
photocell delay timer expires, the alarm timer should be active. In this case the reject
relay is activated.
In order to set this timer up, set the delay time to 0.01s and the alarm time to
something large, e.g. 10.0s. Set the reject time, 0.2s is typical for an air-blast or
pusher reject. Pass a contaminated product (which only just triggers a reject) and
adjust the photocell delay until the reject mechanism operates at the correct time to
reject the product, i.e. if the reject mechanism activates too late then reduce the
photocell time, and vice versa. Note that a 'R' is shown in the top right hand corner of
the display when a reject is triggered.
Once the reject and photocell delay times have been set up, the delay and alarm
times need setting. If these times are not correct then good product preceding or
following the contaminated product may be rejected as well.
Attach a metal sample to the back of the product and pass the product through the
metal detector. The product should be rejected. Increase the delay time by 0.1s and
pass the product again. Keep doing this until the product is not rejected. Decrease
the delay time by 0.15s to allow a safety margin. (If the system has a variable speed
conveyor decrease the taco pulses by 2 to allow a safety margin.)
To set the alarm time a similar procedure is performed. This time the metal sample
should be placed on the front of the product, and the alarm time decreased until the
product is not rejected. To speed up the process, adjust the alarm time in large steps
initially, e.g. 10s, 5s, 2s, 1s. Increase the alarm time by 0.15s (or 2 delay pulses) to
allow a safety margin.
4.4.3 Variable Speed Conveyors
For variable speed conveyors, the timers work in exactly the same way, except that
the delay time, and where applicable the photocell delay time, are measured in tacho
pulses, i.e. these values are based on distance travelled rather than time elapsed.
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