"The Squealer", an Invention that didn't make it to market

In January of 2009 my wife Millie and I were the owner operators of a small Dental Equipment service business. We operated out of our home town and drove 100 miles in any direction to the dental clinics of our customers to repair their chairs, lights, drills, x-ray units, and any other equipment in the clinics. It was a niche business and by providing 24 - 7 service to our clients for the previous 20 years we had come to be the dominate repair service in our area. My wife Millie, a dentist herself, was always at my side as we went from clinic to clinic to analyse and solve the many and varied problems presented by the nice mixture of electronics, hydraulics, pneumatics and mechanics present in the dental equipment.

Over the previous 20 years we were always watching for opportunities to address universal problems in the clinics with innovations that could be marketed. As a result we had at the time three products that we had developed and sold to three different national dental equipment marketers. These products were not big deals but rather just ideas that served to solve simple problems but it was fun to see our work recognized and it was always fun to see a small Royalty check show up in the mail.

Before I can tell you about the Squealer I want to describe the problem in the dental clinics that it was designed to solve. The heart of the dental clinic is the air compressor. Compressed air is used to power the drills, provide pressure to deliver water, actuate air solenoids, and provide a way to blow debris out of cracks and corners in the teeth. If the compressor stops working the clinic can not function and appointments must be rescheduled, staff sent home, and valuable production time is lost.

Here we have a one headed compressor. The small blue horizontal tank on the left is where the dry silica gel purging air is stored and the small vertical tank on the right is the drying chamber where all the silica gel is. When the compressor head turns off the air from the small tank enters the drying chamber at the top and pushes water and vapor out the bottom of the drying chamber and therefore regenerates the drying system for the next compression cycle.

The dental compressor is typically a 220 volt device with one to four heads each of which is a motor directly coupled to an air compression component. The over all compressor is a system that is designed to compress ambient air, filter out impurities, remove moisture from the air and deliver it to the dental operatory. The compressor heads push the ambient air through filters and a drying system that strips out the moisture and stores the compressed air in a storage tank. Whenever the pressure in the tank exceeds 100 pounds per square inch the power to the heads is shut off. When the pressure drops below 80 psi power is restored to the compressor heads and they once again fill the tank to 100 psi. The amount of time that the power is supplied to the heads compared to the time it is off is called the duty cycle of the compressor.

The air drying system of most of the dental compressors relies on the duty cycle to properly function. The hot moist compressed air coming from the compressor head is forced to pass through a chamber that is filled with silica gel. This is the bead like material that is found in those little white packages that come with new electronic device packaging. The silica gel has an affinity for moisture and it is very effective in lowering the dew point of the air. The dew point of the air may enter at 60 degrees F and after passing through the beads it may be well below 0 degrees F. This produces an air supply that is ultimately clean and dry for the dentist to use in his dental procedures. The desiccant in the drying chamber does not have a limitless capacity to strip out the moisture however. Within a short time it begins to saturate and ultimately it can no longer clean the air of moisture. The dental compressor solves this saturation problem by storing a portion of the clean dry air that is being produced in a separate tank and when the compressor hits the 100 psi mark and shuts off this separate supply of dry air is directed back through the desiccant and out into the room. This ability to use 10% of the dry air to regenerate the silica gel seems counter intuitive but in fact it works very well and I have seen compressor systems continue without service to dry the air below the zero dew point for many years. The only requirement is that the duty cycle be low enough so that the regeneration air has enough time to clean the water from the silica gel crystals.

I had noted over the years that there was a prevalent path of failure for most dental compressors. This path usually began quite simply with a leak somewhere in the dental clinic or in the compressor system itself. At this point in the failure a repair would be quick and inexpensive. This leaking air is an added burden on the compressor that adversely affects the duty cycle. As the duty cycle gets longer the drying system gets more and more saturated with water and finally due to lack of time for regeneration it fails. Now the air coming out of the compressor has a high moisture content. The compressor may be running continuously or with very little time off as it tries to keep the clinic pressure above the 80 psi minimum. At this point the compressor system can still be repaired but due to the drying system failure the cost has increased considerably. Unfortunately the dentist and his staff have not yet noticed that there is a problem. As long as the compressor, running constantly now, can keep the pressure above 50 psi the dentist is not likely to notice. Now the compressor, which is not designed to be continuous duty has been running steady for days or weeks. Mechanical failure from wear and tear and heat damage finally steps in and the compressor breaks mechanically and stops. At this point it is usually necessary to buy a new compressor. This can cost from a few thousand to many thousands of dollars and perhaps even more expensive is the down time while a new compressor is shipped in and installed.

My solution to this problem was a device that was called "The Squealer"  Here is a picture of one of the first marketable prototype.

The Squealer was a duty cycle monitor that would measure the amount of time the dental compressor was actively running and compressing air. The time could be set at installation from 1 second to 512 seconds. The controlling device was a "delay on make" timer that would start timing when power was applied and then close the contacts after the prescribed time. If the time limit was not exceeded the unit would reset and wait for the next compressor cycle where it would again time the cycle. If the compressor cycle ran longer than the preset limit the Squealer would emit a very loud 110 db siren. It was necessary for the siren to be very loud as many of these dental compressors were in utility rooms that are isolated from the clinic's staffed areas. You can see that the Squealer would catch a leak problem in the early stage of the failure well before and serious damage would be done. Roughly 50 of these devices were made in my shop and test marketed to the dentists in my service area. They worked well, at least at first, but there were problems as well.

The first problem that I had trying to market these beyond my own area was that they had to be tied into two 220 volt sources on the compressor that was being monitored. I needed a 220 volt source for the siren electronics and I needed to monitor the 220 volts that went to power the compressor head. Dental compressors from different manufacturers wire their machines differently and as such the Squealer would always require a technician capable of working with 220 volts to install them. The Squealer was not a turn key device that could be marketed to the dentist. Still every one of my dentists who had a Squealer were no longer in danger of loosing their compressor to a simple long term air leak and there were several over time who benefited from this protection. After a year of so in the field it was noticed that there was a second problem with the Squealer. I had mounted most of the units directly on the compressor. Over a years time the vibrations of the compressor had broken wires and caused components to break loose. This became enough of a problem that I went back to the drawing board and redesigned the Squealer.

Enter "The Squealer II".

The Squealer II was smaller and simpler. It only required a hookup to the 220 volts power that was supplied to the compressor head. The internal electronics were on a circuit board and there was a simple timing circuit that was adjustable to set the time duration before the alarm would sound. This unit was a definite improvement over the first model and a large portion of the originals were replaced with the Squealer II model. The problem however remained that it was still not a turn key unit as it still required a technician to tap into the 220 volt feed to the compressor head.

In the mean time I had been busy contacting potential marketers for the product. The dental industry is very controlled and it is difficult to get anything to market without the interest of one of the major players. I had gotten one of these players interested but I could not get them to move on the project. I knew that long term the unit needed to be redesigned to a turn key configuration but at the time I did not have the electronics skill to do this. I hoped the marketing partner would find someone to take the idea and help me redesign it but this never happened. The project never got off the ground with this vendor and after wasting more than a year I pulled the commitment back and went back to searching for a marketing partner.

I was determined that I would improve my electronics enough to make the unit a turn key device that could be purchased by the dentist and installed without the need of a technician or the need to make a hard wire attachment to the compressor. I began this process in 2013 and by September I made contact with a new web site (element 14) as I searched for answers to some of my electronics questions. At the time I addressed my first question, related to an Arduino I was attempting to use, to Jeremy Blum. Jeremy never answered me but mcb1 did. My continued education and experimenting with the help of Mark and others at element 14 eventually produced the Squealer III.

The Squealer III was an Arduino based unit that monitored the compressor duty cycle with a microphone. It was turn key as it could be installed by connecting it to a 9 volt wall wart, and putting the microphone in the vicinity of the compressor. The sensitivity of the microphone had to be adjusted so that it detected only the difference between normal utility room ambient noise and the noise of the compressor running. The time limit was programmable with dip switches under one of the covers of the case. I made 5 of these units and test marketed 3 of them for a six month period to make sure there weren't any serious side effects or problems.

While I continued to search for a marketing partner I eventually lost interest and put the project on the shelf. The companies in the industry who should have been interested in this product were not. It served their bottom line better to have the dental compressors fail catastrophically. There was little money in doing minor repairs on compressors compared to selling multi-thousand dollar replacements. The compressor manufacturers and the equipment retailers were not interested. I had been around several times to most of the after market and supplemental market companies with no luck in getting any interest.

I knew that the dentists themselves would benefit greatly from this product but its benefits were not immediate and in many ways it was like selling insurance. One of the concerns of anyone that is trying to market a new product themselves aside from the initial costs are the liabilities involved. Suppose I sell a unit touting its ability to give an early warning of a failure. The purchaser buys it and installs it on his 20 year old compressor. A week later the old compressor dies of natural causes and the dentist decides to sue me for promising him that he would get an early warning of the failure. I decided that I would not chase this dream any further. By this time I was retired and I was still having fun working with my new improved electronic skills and interacting on the e14 forum. I just did not want to work as hard as was going to be necessary.

I was inspired to write this blog by two things that have recently happened. The first was seeing a new device at a trade show that has been pictured here on the forum from Avnet.

https://www.newark.com/avnet/avtsea01a-m01a-s01a-c00/smartedge-agile-meta-sensor-iot/dp/84AC0532?st=Avnet

It, like my Squealer, was capable of monitoring a piece of machinery like a compressor for a variety of parameters. In addition to many more sensors this new device was capable of reporting the condition of that machine through a wireless link to a smart phone or a computer. For anyone who works in situations where a critical piece of machinery like a dental compressor should be monitored this little device is a necessity.

The second thing that triggered this blog was the release of "Exploring Arduino 2nd ED" which reminded me of how I came to be a member of element 14 in the first place. Many thanks to mcb1 and element 14 for their help on my Squealer project and many other projects in the ensuing years.

https://www.element14.com/community/message/285579/l/jeremy-blums-second-edition-of-exploring-arduino#285579

While I never got my idea of a duty cycle monitor to market the last 10 years has allowed technology to surge forward and over run my idea with a much more universal and flexible solution.

John