FAQ-I004
How many sensors should an IBC system have?

Q:  How many IBC sensors should a system have?

A: Depending on how you wish to look at it, the number varies from one to four. It all depends on what you are wanting to accomplish.  If you are running commodity product with a loose layflat variation target, one sensor will get the job done.  If you are running a product that requires tight layflat control, the multiple sensors will help in that endeavor.  If you are interested in making a more refined decision, you also need to consider the condition and configuration of your sizing cage, the amount of transverse gauge variation, the production rate you need and the product configuration.   All models of the IS-IBC1® system sold by D. R. Joseph can be fit with one to four IBC sensors and are also field upgradeable.  Patented signal processing makes it possible for the system to produce tight layflat control with only one sensor.  However, in the cases outlined below, additional sensors can help offset the effects of uneven bubble shape and sway.

Sizing Cage Condition

If the sizing cage is an older style with nylon or teflon rollers and the production you are running demands no scratches in the film, the operator will run the bubble slightly or completely away from the cage.  This defeats the main benefit of the cage which is to hold the bubble steady over the air ring and to allow higher production rates as a result.  If the cage cannot be repaired or replaced with a soft woolen ROLL cage (contact us about this amazing new style of cage), using multiple IBC sensors will help account for the bubble sway that occurs.  For information about sizing cage configuration, see the section below.

Transverse Gauge Variation and Very Large Bubbles

If your transverse gauge variation is such that the bubble shape is not round and from day to day you cannot depend on the consistency of the bubble shape, multiple sensors will help average out the day to day changes in bubble shape.  Those who are oscillating the die are particularly susceptible to bubble bulges and in this case, multiple sensors are a must.  Those who are running very large bubbles are unavoidably affected by air currents in the plant.  The bubble is so large that it acts like a sail and even if the gauge is perfect, the shape is not.  Multiple sensors are imperative in this situation as well.

Production Rate Considerations

Running higher production rates always requires more cooling to be brought to bear onto the bubble.  The additional cooling can reduce bubble stability.  If the cage is not in good condition to properly support the bubble, the melt stability will be the significant factor in how much production you get.  In this case, where the sizing cage is not able to stabilize the bubble, multiple sensors will help reduce IBC system reaction when the bubble sways.  This will result in a higher production rate than would be possible with only one sensor.   However, layflat control will suffer when the bubble is allowed to sway, and if you are running a product with a tight specification on layflat, you will have to slow the line down to reduce bubble sway.   Multiple sensors help, but they do not eliminate the effects of bubble sway on layflat variation.

Product Configuration

Product configuration also plays a part in the decision process.  Obviously, if you are running tubing, you want the tightest layflat control possible and a good sizing cage and multiple sensors can help.  However, if you are running sheeting,  you also need to consider if the material you are running can be recycled or not.  If it cannot be easily recycled, minimizing trim is a big issue.  Not all materials can be successfully edge slit so trim may be unavoidable.  If this is your situation, a good sizing cage and tight layflat control are required and multiple sensors will also help.

Cage Configuration

The specific configuration of your cage has a lot to do with how many sensors you can install.  The optimum method for mounting multiple sensors is to evenly space the sensors around the bubble.  Two sensors would be spaced 180 degrees apart, three would be spaced 120 degrees and 4 would be spaced 90 degrees.  However, not all cages that support two sensors will allow you to mount three sensors evenly spaced.  Generally speaking all cages support one sensor.  If the cage has a multiple of three arms around the bubble, it can handle one or three sensors.  If it has a multiple of four arms around the bubble, it can handle one, two or four sensors.    

Date of Last Update: 06/01/2005

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