by Richard Carrara, President

Industrial Sensors Inc.


Being able to respond to marketplace opportunities with "The ISI Advantage" is what gives our company its competitive edge. This advantage can be summarized with four words:

An important ingredient of "The ISI Advantage" is the vast storehouse of knowledge and on-site experience accumulated by ISI's people during more than 25 years of visiting extrusion plants which, by any measure, are among the most hostile environments for equipment and instrumentation, including our own melt pressure sensors.

Observing first-hand how these conditions can affect operating efficiency has given ISI personnel the experience to advise plant operators on ways to make their process environments safer and more efficient by avoiding or eliminating conditions that create downtime and erode productivity and profitability.

The purpose of this discussion is to familiarize you with these conditions so that you can be more effective problem solver. ISI personnel are experts in solving problems which commonly plague extrusion plant operations in these five areas:

1. Noise Interference

2. Mounting Holes

3. Transducer Installation

4. Diaphragm Considerations

5. Transducer Calibration


Noise interference is often misunderstood or misdiagnosed because it seems so mysterious and complex. In reality, the problem is quite easy to solve by following well known and simple procedures.

Noise problems caused by electrical interference are usually traceable to poor grounding, inadequate and/or insufficient electromagnetic protection in the signal processor and/or the readout instrument.

Electromagnetic Protection:

Every single instrument and transducer (transmitter) that carries the ISI name has received the C.E. mark of approval. This means that ISI products are immune to electromagnetic energy and noise caused by motors, switches, heaters, compressors, walkie-talkies and unbalanced factory loads. DC motors are particularly troublesome, but independent outside testing has shown that ISI products are exceptionally well protected against energy spikes induced by rapid switching of the DC motor control current (pulse width modulation).


Because all melt pressure sensors are grounded at the tip, they are in fact grounded when they come into contact with the extruder. For this reason, it is imperative that the shield of the cable which connects the transducer of the instrument be attached to the sensor via the connector. This can be accomplished simply by attaching the shield under one of the screw terminals located on the transducer. Do not connect the shield to the readout instrument.

It is important that the shield be grounded at one end. Otherwise, a ground loop may be created through the shield which would defeat the purpose of a single ended grounded shield called a "Faraday Cage," (named for its developer Michael Faraday). This is a common technique used to extract noise, collect it via the shield and bring it harmlessly to ground.

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