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This is the third chapter in my presentation on Poppery 1 modifications.

The following couple of pictures are of fully modified P1s. These machines use different switches, different model PID controllers and different ‘type’ thermocouples. They are however, along with a dozen or so others that I know of, work alike clones of each other.
Fully modified P1s such as these are capable of roasting one half pound (net) roasts, back to back all day long. After reaching the end of roast, adjusting the fan to high speed will cool the roast to 250° F in a couple of minutes and is ready to roast again as quickly as you can unload the roasted beans into whatever you use for further cooling and reload it with greens.

The roasting process (profile) itself can be infinitely modified and stored in the PID easily by interfacing the PID controller to a computer armed with some simple software. Very simple software is provided free with the controller and there is ‘Coffee Specific’ software in development (the Beta versions work great).

The capabilities of this roaster depend on several key modifications. The first of these is enlarging the effective roast chamber size by adding a substantial chimney. The second necessary modification is variable speed fan control including the ability to ‘push’ the fan to 138 to 140 volts. And the third mod is controlling the heater section of the roaster with a programmable PID controller capable of a minimum of 4 ramp/soak segments (preferably twice that many). The ability to interface to a computer to facilitate PID programming requires it to be optioned with communication capabilities, otherwise the PID can be programmed from its front panel.

The way I am going to write the remainder of this article is to: populate this thread with various pictures of the process, organize them to follow the three previously mentioned major modifications and finish by throwing the necessary verbosity in between the pictures. I'll be re-organizing and editing this post frequently and the more participation I get from readers the more interesting this process should be. This is obviously a fairly dramatic departure from the way articles are normally written - - we'll see how it works out.







1 Bakelite Base Housing

Increasing the air flow to allow a larger bean load while roasting in the P1 is one of our goals. To facilitate this, opening up the supply side for the fan is beneficial. In my testing, this modification by itself has increased the roasters green bean load by 25 gms in an otherwise completely modified P1. A variation, to accomplish the same result is to leave the sheet metal piece off of the bakelite base and perforate the bottom plastic piece (which the rubber feet attach to) and covering these perforations with a screen to disallow garbage being sucked into the roaster. I prefer the method shown in the pictures because it circumvents the problem of sucking garbage into the roaster and is considerably quieter. With the addition of a small amount of padding around the inside of the base of the outer plastic housing the noise of the fan can be further dampened.







2 Outer Plastic Housing

The measurement shown in this picture has been accurate for several roasters, but - - keep in mind that the outer plastic housing will be held in place by its interference with the horizontal flange (just below the air inlet holes) of the bakelite base housing. Differences in the original moulds for the base housing may require the outer housing to be cut to a different height. The accurate way of cutting the outer plastic housing is to fit it onto the base housing (roast chamber in place) with a small amount of downward pressure, being sure to center it. When everything is even, lay a pen or scribe across the top of the roast chamber opening and mark the inside of the plastic housing. Remove the housing, cut off and dispose of the upper portion of the housing.




3 Top Plate










4 Chimney




5 Chimney Clamp













6 Dual and single power cords



7 Control Box







I have recently acquired a Fuji PXG5 PID controller and built an enclosure for it. It is a DIN 8 size, so something larger than the standard Radio Shack box was required. The obvious add-on at the top of the box containing the row of togle switches, will be removed when I figure out which switches I want to permanently mount on the box. The PXG5 is set up with 5 digital inputs and these are temporary switches to manipulate the 5 optional controls.




8 Variable Speed Fan control







9 Thermocouple placement







10 TC cords and plug/receptacles



11 PID SELECTION

It has taken me quite some time to figure out how to address the issue of PID selection. There are dozens of manufacturers that offer PID controllers and each one of them has several models, with many options. To the uninitiated, the selection of an appropriate controller can be an insurmountable roadblock to a roaster project. I am going to make some suggestions as to manufacturer, model and options......but first I'll try to explain in as much of a non-geek fashion as possible what a PID controller is.

A PID controller used in a roaster is no more than a hot rodded thermostat. A simple thermostat will have a 'band' within which the temperature is controlled. A thermostat that is set for 100°F with a 10°F band will turn the heater on when the system cools to 95°F and turn the heater off when it reaches 105°F. A PID controller is designed to maintain the temperature with considerably less variation. Ideally, a PID controller would heat the system up to the target temperature of 100°F exactly and keep it there (no band).

The acronym PID stands for the type of math that the micro-controller does to control the output. This miniature computer system does P (Proportional), I (Integral) and D (derivative) math on the values of current temperature, target temperature, rate of change of temperature, response of the controlled system to changes in the heat input etc. etc.........and a whole bunch of other things. If this type of thing trips your trigger, there is an overpowering amount of information on the math and how to implement it in different systems available with a simple google search.

When roasting coffee we need to be able to change the rate at which the coffee is heated several times during the roast. A substantial portion of the PID controllers available today can be discounted immediately due to their inability to provide 'Ramp / Soak' abilities (or other descriptors meaning the same thing). This 'Ramp / Soak' ability of the remaining controller candidates allows us to do things such as heat up from 100°F to 200°F in 4 minutes (a 25°F per minute Ramp), Soak at that temperature for 0 minutes (no soak), and continue from 200°F to 300° in 5 minutes (a 20°F per minute Ramp). Most coffee roasting profiles can be accomplished with from four to six ramps. An example profile condensed to ramps is:

Ambient temperature to 230°F - - - 2 minutes
230°F to 300°F - - - 2 minutes
300°F to 405°F - - - 4 minutes
405°F to 445°F - - - 6 minutes

This roasting profile uses four ramps. When looking at PID controllers this is the minimum that will allow any flexibility in developing different roasting profiles. In many industrial applications a heat up Ramp is followed by a 'Soak' at the end prior to continuing the heat up with another ramp, this ramp / soak is described as two segments by many manufacturers. So, a controller capable of four ramps can be described as being capable of eight segments. Many of the current crop of PID controllers have 32 segment capability and the higher cost units may be able to store and switch between different ramp / soak profiles. The math being performed by the controller has a bunch of variables that allow it to be used in different types of systems. In older controllers, these variables are quantified by measuring temperatures and times as you heat up and maintain a given temperature in whatever system the controller is manipulating. The instruction book will walk you through the simple formulae used to produce these values. Newer controllers will have some type of automatic learning process that greatly simplifies the PID controller setup. Some of the newer controllers even have a 'fuzzy logic' feature that compensates for minor real time variations the controlled system may see. Another ability of some the most current PID controllers is measuring time in seconds rather than the traditional minimum time increments of minutes.

I hope you understand that the above is a pretty basic description of these controllers. If you are shopping for a controller on EBay or other auction or surplus location, this description should give you some basic information to help identify a controller that may fit your needs. Due to the tremendous flexibility of PID controllers, there are frequently many dozens of optional configurations for any given controller. Before you buy anything, identify the manufacturer, the model no. and any other descriptors on the name tag that may be used to identify how it was optioned when originally purchased. Go to the manufacturer’s web site and download the manual for the controller. Read the manual and ensure that the controller is capable of accomplishing the required tasks. If you can't come up with a manual for the PID - don't buy it. PID controllers have from 30 to 200 individual parameters that may need to be turned off/on set or reset. Some controllers are optioned with RS 232 or RS 485 communication interfaces which allow manipulating and/or monitoring the controller via a computer or master controller, if you are planning on using this feature........make sure the software and whatever is necessary to 'talk' to the controller is available at a price you can live with (some companies provide free software - some companies want a second mortgage on your house for their software). PID controllers can normally be reprogrammed from the two or three buttons on the front face - changing a few parameters is fairly easy once you've accomplished it a few times. Checking, changing and experimenting with all of the settings from the front panel can be daunting, and impossible without a manual. BTW, when I say manual I don't mean just the sales brochure, the manuals for these things commonly go to a hundred pages or more.

I hope the above has not scared you away from trying your hand with a low cost surplus controller that may cut the cost of your roaster project in half. I know a dozen folks who have built clones of my 'Ubber Popper' using PID controllers that cost less than 20% of what the Fuji model that I use. All of these folks are pretty technically proficient and several weren't successful until buying a second or third controller.

When I built my first P1 based roaster, I used a variac to control heat. When I decided to use a PID controller with the P1 I had read everything I could by a plethora of folks who had used the Fuji controllers for espresso machine heat control and the half dozen or so people who had done similar roaster projects. I hesitate to name names in fear of forgetting someone. I am certainly not the first. Most people in the coffee community have defaulted to the Fuji PXR series of PID controllers. The reasons for this are probably pretty similar to mine, it is comfortable to have a community of folks who are familiar with the pitfalls of a complicated piece of equipment, and can help - - if problems arise. I am sure that all the major manufacturers produce a controller that is fully as capable as the Fuji. Omega, Watlow and many others are legend in the technology of temperature control and their equipment is undoubtedly fully capable.

I have built a couple dozen clones of the 'Ubber Popper' and have used the Fuji PXR3 controller on all but four of them which use the Fuji PXR4. The only difference between the two (for our purposes) is that the '4' is a DIN 16 (48mm x 48mm) size with two lines of display, while the '3' is half height DIN 32 (48mm x 24mm) size with one line of display. The advantage to the '4' is that it displays the actual temperature on one line and the 'Set Value' (what the controller thinks the temperature should be at any given time) on the other line. With a '3' the two temperatures can be toggled to the display by pressing one of the three buttons on the bottom of the controllers face.

OPTIONING THE CONTROLLER

INPUT
I have found that thermocouple input is the most cost effective - for me. The Fuji and many other recent generations of controllers can be reset to use different 'types' of thermocouples (J, K, T etc.). K thermocouples are the most appropriate and popular for roasting use, but if you already have another 'type' - - use it. Some PIDs have to be optioned for the specific input that you plan on using. Be sure to check this if you are planning on using a surplus PID. Some temperature input devices (even some types of thermocouples) can be prohibitively expensive.

OUTPUT
SSR (Solid State Relay) output is my normally used output. I'm currently testing an SCR (analog control) with high expectations. Many PIDs can be optioned with an 'onboard' relay capable of a 1 Amp or so current flow. This is obviously not enough to control a roaster heater of 1400 or 1500 Watts. If your PID has this as the output option, you can use it to trigger a larger (15 Amp or larger) relay or SSR. This 'onboard relay' is a mechanical relay and has a set of contactor points that will wear out considerably faster than the solid state device used with an SSR output option.

Most PIDs can be optioned with one of several analog output signals such as 1 to 5 Volts DC, 1 to 10 Volts DC or 4 to 20 mA DC. This type of output signal can be used by a current carrying device such as an SCR controller to provide a variable voltage to the roasters heater rather than the off/on power that the SSR provides.

An SCR type heater control scheme provides a smoothly variable heat output from the heater and may keep the system from seeing heat excursions such as is seen with the heater being either fully off or fully on when using an SSR or other relay control scheme.
The disadvantage to SCR control is its cost. SCR devices capable of 15 Amps are available today in the $75 price range. An SSR of this size is in the $25 range. The heat excursion tendency of the SSR control scheme can be minimized by setting the off/on cycle time (period) to a short time such as one half second. There has been debate about these two control schemes and I would recommend that you research it and make your own decision.

RAMP / SOAK
As I have mentioned previously, a controller that allows at least four ramps is necessary - more is better.

AUTO TUNE
A controller with the auto tune feature greatly simplifies set up initially. This feature is also useful to re-tune your roaster to compensate for things like a change in inlet air temperature from summer to winter if you roast in a location without a fairly consistent ambient temperature. Substantial changes to your roasters green bean load or other changes to the roaster systems environment can be quickly and easily compensated for with the auto tune feature.

FUZZY LOGIC
Many of the last couple of generations of PIDs have a 'fuzzy logic' feature that allows the PID to do minor compensations to control setup in real time during operations. I have had good luck using this feature; some other folks believe they do better with the fuzzy logic feature turned off.

COMMUNICATIONS
RS 485 is a communications protocol that is widely used in industrial environments to communicate between various types of controllers such as computers and devices such as PIDs. It is similar to the RS 232 serial communications found on most home PCs and inexpensive converters can be purchased which allow a computer with a serial (or even USB ) to talk with an RS 485 communications system. RS 485 communications is a two way protocol (the PC and the controller can talk to each other).

Another communications protocol that is becoming popular in the newest PIDs is the 'loader' port. The loader port is usually an RS 232 port on the controller (frequently a small stereo head set type connector) that allows loading the complete parameter set into the PID. Some specific units include the ability of the controller talking to the computer in real time in the same manner as RS 485.

Being able to communicate with your PID from your PC allows easy setup, roast monitoring including data logging individual roasts and even complete computer control of the roaster system in some circumstances. I recently made a fairly significant change to my base (most commonly used) roasting profile and needed to proliferate this change to the couple dozen clones of my roaster that people are using. All of the roasters that I build use PIDs with the RS 485 communications option, so it was relatively easy to email the new profile to the folks involved and talk the less technically inclined among them through the process of updating their PIDs.

Marc Cohen has produced a roaster specific software program that takes this one step further. His program is specific for the Fuji PXR series of PIDs with RS 485 communications option. The program allows real time PC interface and control of these PIDs and includes the ability to change profiles and use specific profiles for specific beans, green bean stash management, graphing and logging roasts and many other coffee geek types of functions.

OTHER OPTIONS

The only other PID options that I regularly use are the DI (digital input) and DO/ALARM (digital output) functions. The DI is the ability of the PID to see whether two terminals are shorted of not, so if you hook a toggle switch to these two terminals the PID can be programmed to perform a variety of operations depending on the position of the toggle switch. I use this to start of stop the ramp / soak profile. Other uses for the digital inputs are operations such as resetting alarm states, standby off/on and various other operations that are specific to different PIDs. I have been experimenting with a DO (digital output) signal to switch a resistor into my roasters fan circuit to manipulate fan speed during the roast. PIDs can commonly be optioned with several DIs and DOs.

SPECIFIC RECOMMENDATIONS

As you have already figured out from the above description, there are a lot of PID controllers that will function well in a coffee roaster. Making specific recommendations among the field of available controllers would take considerably more experience with the various makes and models than I have. I can, however, recommend the controllers that I use; the Fuji models PXR3 and PXR4. As I have indicated above, the only advantage to the PXR4 over the PXR3 is that the former has a two line display allowing it to indicate the set temperature and the actual temperature at the same time, this increased indication costs $40.

The options that I include when ordering a PID are:

Input - Thermocouple, Farenheit indication
Output #1 - SSR (Solid State Relay)
Output #2 - None
Alarms - None
Power Supply - Standard (100 - 240 Volt, 50/60Hz)
Additional Functions - RS485 Communications and a single Digital Input (DI)

The model # for a PXR3 with these options is: PXR3-RCY1-4VVA1

The model # for a PXR4 with these options is: PXR4-RCY1-4VVA1

I purchase my controllers from TTI Global, their phone #'s are 802-863-0085 and 800-884-4967 and web site is http://www.ttiglobal.com . The gentlemen that I order from if doing so on the phone are Dwight or Shawn (I'm sure there are other folks there that are capable of dealing with orders). You can get the PXR setup with my profile by requesting it to be programmed with "ubber popper.pxr", I believe they keep a copy of Jim Schuleman's program also.

Fuji has recently come out with a new series of PID controllers, dubbed the "PXG" series. The PXG controllers have all the advantages of the PXRs with the advantage of being able to reset the time increments to minutes and seconds rather than the minimum time increments of hours and minutes of the PXR series. The PXG also has a built in RS 232 "loader" port, which will allow easy loading of new profiles to the controller, and so far it seems to provide the two way communications needed for computer monitoring and/or real time control during the roast.

I recently purchased a PXG5 controller with a firly broad range of options which I plan on thoroughly testing in a roaster, so I may have new information on this in the near future.

Mike
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