Trouble Shooting Vibratory Feeders Part 3 -Intermittent Operation
INTERMITTENT OPERATION
Intermittent operation is almost always electrical. Generally the symptom is that the feeder will increase its amplitude to the maximum amplitude for no apparent reason. Occasionally it will simply return to the correct amplitude again for no apparent reason or it will simply run at maximum amplitude no matter where the control is set.
The causes of intermittent operation generally fall into the following categories:
Intermittent operation is sometimes an indication that the SCR Controller is about to fail. Generally, once it exhibits inconsistencies, the controller has at most two weeks or so of operation left. Maintaining a spare controller of each type is a wise and economical policy to practice.
Also this kind of problem can occur very early in the life of the feeder, sometimes in the first month or less.
It is usually easy to diagnose.
External sources can cause intermittent operation on feeders with SCR Controllers. Resistance welding, arc welding, ultrasonic cleaners, and other high frequency equipment can generate electrical noise which will affect the SCR and turn it on. It the feeder goes to maximum amplitude while the resistance welder is being cycled, it is rather easy to notice this if you are aware of the possibility of it being a problem. The point should be made, however, that the source of the noise does not necessarily have to be in the same room as the feeder. It can be on the same electrical line and sometimes be quite a distance away. It is practical to filter the noise by installing capacitors across the incoming line to the feeder. And should and often will eliminate the problem. Most controllers are designed to filter out this noise.
Rectifiers and other electronic components age with time, and sometimes their maximum performance declines over several years. It is not often that a controller is replaced because of this but it can occur if the feeder is run at maximum performance at all times. This is determined by an electrical check, and should be done by the electrician.
Another potential cause for unsatisfactory performance is low line voltage in a plant. If the feeder is operated at maximum performance, then it usually requires a minimum of 115 volts AC on the incoming line. However, in many plants this voltage may drop to below 100 volts when machines, ovens, and other large current devices are in operation. Generally, it will be noticed as these items are turned off and the performance of the feeder comes back. If this is the case, it is sometimes necessary to install a constant voltage transformer ahead of the feeder. This will keep its performance even through wide fluctuations of the input voltage.
