Coffee Roaster - Gas Control Project - Seeking Guidance/Advice

Thread Starter

james211

Joined May 29, 2012
250
Hello (not sure this is the right forum but I'll start here)

So I’m going to start out by saying that I am no programmer, and I won’t be doing this all myself, I will most likely have to hire someone, but this isn’t a search for that. Right now I’m in search of acquiring the proper hardware to successfully complete this project.

I run a small coffee roasting business, using an LP powered gas roaster. In order to achieve really good results with roasting, gas control is extremely important. So what I’m looking to do is install an electronic proportioning valve so I can precisely control my gas flow to very specific pressures. Having this control will give me repeatability that is necessary for consistent coffee roasts. I do use a logging software, but I want this to be aside from that. Often times the software gets updated and software control gets broken and then things don’t work. Having this be a stand alone controller will help future proof things a bit.

The Project
What I’m looking to accomplish is to create small device with a touch screen that I can send commands, in 5% increments, to an electronic proportioning valve to make gas pressure adjustments for me. I have further plans, but for the time being this will be it.
With the help of a former mechanical engineer I have settled on the appropriate EVP valve.
Clippard EVP Valve - https://www.clippard.com/part/ET-P-05-1325. This valve is PWM controlled, the company also sells a driver board which I will purchase, but I still need to send signals, and I’m not sure what the best platform for this is, Arduino, Beaglebones, RaspberryPi, some other option?
In addition to the EVP, I’m going to need a calibratable pressure sensor to send feedback to the controller (Arduino…etc) to ensure the adjustments are accurate based on the maximum pressure from the regulator.

I don’t foresee this being too difficult, but in order to acquire the proper hardware I need some guidance and I’m hopeful this community of intelligent people will help me out.

Thank you in advance, and I hope everyone is staying safe and healthy in these trying times.
 
Have you thought about a thermal mass flow meter? e.g.https://www.eprintersupply.com/pages/shipping

Generally, they are purchased with a particular calibration and/or user calibrated. I used MFC's from UNIT, MKS or Tylan.
Hydrogen units were special. Tylan units would not completely shut off. The valve they used for control was thermal based.

Ours had voltage output and were typically controlled by a potentiometer. They were 0-5V in, 0-5V out, but their readout assembly mitigates the differences in ground when more than one unit is used with one power supply.
 

ci139

Joined Jul 11, 2016
1,470
In addition to the EVP, I’m going to need a calibratable pressure sensor to send feedback to the controller (Arduino…etc) to ensure the adjustments are accurate based on the maximum pressure from the regulator.
such may become a headache very fast if your gas comes from the source where the pressure may vary
also if you open the valve ever more - the pressure behind (the source side of) it drops
to cover all ↑this↑ + the feedback "hysteresis/inertia"
. . . takes a g.d. reseach on your particular system

+ other than that . . . if your DIY control fails how you keep your production going --e.g.-- the "Plan B"
 

wayneh

Joined Sep 9, 2010
16,390
Hello (not sure this is the right forum but I'll start here)

So I’m going to start out by saying that I am no programmer, and I won’t be doing this all myself, I will most likely have to hire someone, but this isn’t a search for that. Right now I’m in search of acquiring the proper hardware to successfully complete this project.

I run a small coffee roasting business, using an LP powered gas roaster. In order to achieve really good results with roasting, gas control is extremely important. So what I’m looking to do is install an electronic proportioning valve so I can precisely control my gas flow to very specific pressures. Having this control will give me repeatability that is necessary for consistent coffee roasts. I do use a logging software, but I want this to be aside from that. Often times the software gets updated and software control gets broken and then things don’t work. Having this be a stand alone controller will help future proof things a bit.

The Project
What I’m looking to accomplish is to create small device with a touch screen that I can send commands, in 5% increments, to an electronic proportioning valve to make gas pressure adjustments for me. I have further plans, but for the time being this will be it.
With the help of a former mechanical engineer I have settled on the appropriate EVP valve.
Clippard EVP Valve - https://www.clippard.com/part/ET-P-05-1325. This valve is PWM controlled, the company also sells a driver board which I will purchase, but I still need to send signals, and I’m not sure what the best platform for this is, Arduino, Beaglebones, RaspberryPi, some other option?
In addition to the EVP, I’m going to need a calibratable pressure sensor to send feedback to the controller (Arduino…etc) to ensure the adjustments are accurate based on the maximum pressure from the regulator.

I don’t foresee this being too difficult, but in order to acquire the proper hardware I need some guidance and I’m hopeful this community of intelligent people will help me out.

Thank you in advance, and I hope everyone is staying safe and healthy in these trying times.
Are you certain that the best control strategy is gas pressure? I mean, the beans see only the bulk temperature and perhaps the surface temperature inside the roaster. They don’t care about the pressure.

You could have perfect control over pressure but be out of control on temperature. I’m not saying it won’t work - I’m sure it does - I’m just suggesting thinking out of the box since you’re starting a new project anyway.
 

drc_567

Joined Dec 29, 2008
848
Depending on the economics, the burner linked to here seems to have a more precise degree of temperature control. Coffee roasters are listed in the product description. :
propane burner
 
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Thread Starter

james211

Joined May 29, 2012
250
Have you thought about a thermal mass flow meter? e.g.https://www.eprintersupply.com/pages/shipping

Generally, they are purchased with a particular calibration and/or user calibrated. I used MFC's from UNIT, MKS or Tylan.
Hydrogen units were special. Tylan units would not completely shut off. The valve they used for control was thermal based.

Ours had voltage output and were typically controlled by a potentiometer. They were 0-5V in, 0-5V out, but their readout assembly mitigates the differences in ground when more than one unit is used with one power supply.
I have considered this, the ones that were recommended to me we’re terribly expensive though. I’ll have a look at your recommendations though.
 

Thread Starter

james211

Joined May 29, 2012
250
such may become a headache very fast if your gas comes from the source where the pressure may vary
also if you open the valve ever more - the pressure behind (the source side of) it drops
to cover all ↑this↑ + the feedback "hysteresis/inertia"
. . . takes a g.d. reseach on your particular system

+ other than that . . . if your DIY control fails how you keep your production going --e.g.-- the "Plan B"
thankfully the source is very reliable, it’s an LP tank with significantly higher pressure than I need. There is a regulator that brings the pressure down significantly.

this sort of hardware is implemented on many roasters with more advanced controls.
 

drc_567

Joined Dec 29, 2008
848
There may be a another way to reach your control requirement.
Assuming a reasonably stable source pressure ... meaning the ambient temperature variation is not excessively erratic, determine an orifice diameter that will comply with the 5% gas flow rate specification. This should be a feasible task. There are charts with orifice plate diameters to reference. Then, search for and locate a suitable solenoid valve that can either allow or stop the gas flow in an individual orifice tube. Arrange for a manifold with several of the individual orifice plate/ solenoid valve assemblies in parallel. The outlet header of the manifold is directly hooked to the gas burner. As each orifice tube is electrically opened, the overall flow rate should increase by 5%.
... Have not located an appropriate solenoid valve at this time, but it seems like there should be one someplace.
 
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I have considered this, the ones that were recommended to me we’re terribly expensive though. I’ll have a look at your recommendations though.
That was just my first hit. We used a lot of these: https://www.digchip.com/datasheets/parts/datasheet/798/FC260.php
They were easy to fix too.

Somebody at work put 6 DPM (Digital panel Meters) in a box, 1 bipolar supply, 1 5v supply and 6 turns counting dials and potentiometers and some rectangular connectors. It worked well for manual control. I made some changes making it easier to set full scale, set the decimal point and calibrate, but I goofed when I tried adding an external setpoint.
 

ci139

Joined Jul 11, 2016
1,470
the professional equipment has reason for it's high cost -- usually involving a lot of development hours to gain reliable , long and safe service life and correspondence to regulations . . . everything needs maintenance , but the failure-free service time for ←such equipment is significantly higer ... usually
 
That's a really cool mass flow controller. We were controlling hydride gasses (e.g. Silane) and Hydrogen, so we had to calibrate each gas using pressure rise time. I had a switch the switched in +5V full scale and input. There was a 10 turn trimpot to set full scale and DIP switch to set the decimal point. Setting the decimal, you had to open up the box.

If memory serves me right, I put an active circuit inside the connector to make a Brooks MFC connect to a Tylan readout,

We also used them for Hydrogen Selenide. The Tylan ones never shut off completely. They had an inherent "hiccup" which is documented, but didn't concern us.
 

MisterBill2

Joined Jan 23, 2018
6,107
Since the variable that you want to control is roasting temperature the reasonable approach is to sense roasting temperature. The way to do that with reasonable accuracy is with a fast response sensor and a controller able to respond to very small changes fast enough. The final requirement is a way to vary the heat input from less than is needed to a bit more than is needed.
The controller output will then be a time-proportional signal switching between the lower heat input and the higher heat input.
I created a test machine using this scheme to control the temperature of a 5 gallon oil tank and it was able to hold the temperature within about 3 degrees C very well, as the test load varied.
The big requirement is that every element be able to correctly respond faster than the process can follow.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Since the variable that you want to control is roasting temperature the reasonable approach is to sense roasting temperature. The way to do that with reasonable accuracy is with a fast response sensor and a controller able to respond to very small changes fast enough. The final requirement is a way to vary the heat input from less than is needed to a bit more than is needed.
The controller output will then be a time-proportional signal switching between the lower heat input and the higher heat input.
I created a test machine using this scheme to control the temperature of a 5 gallon oil tank and it was able to hold the temperature within about 3 degrees C very well, as the test load varied.
The big requirement is that every element be able to correctly respond faster than the process can follow.
The target temperature in coffee roasting is a constantly moving target, whereas the gas pressure (which serves as a reasonably good proxy for heat input) can stay relatively constant for chunks of time (depending on roasting equipment and preferred style.) I've written in more detail in previous threads. See post 9 in the thread below:

https://forum.allaboutcircuits.com/threads/controlling-2-6k-heating-elements-using-ssr-heat-sink-s-potentiometer.146071/#post-1242834

Suffice it to say that simple temperature control methods aren't very helpful in coffee roasting.
 

MisterBill2

Joined Jan 23, 2018
6,107
The target temperature in coffee roasting is a constantly moving target, whereas the gas pressure (which serves as a reasonably good proxy for heat input) can stay relatively constant for chunks of time (depending on roasting equipment and preferred style.) I've written in more detail in previous threads. See post 9 in the thread below:

https://forum.allaboutcircuits.com/threads/controlling-2-6k-heating-elements-using-ssr-heat-sink-s-potentiometer.146071/#post-1242834

Suffice it to say that simple temperature control methods aren't very helpful in coffee roasting.
Presuming that the TS knows what the temperature profile for roasting is supposed to be, there are controllers available that can provide a string of individually settable setpoints. AND there are temperature controllers available that can continuously follow the temperature setpoint downloaded from a computer, which would be running a coffee roasting temperature profile program.

Adjusting the heating gas flow to hold a temperature for a process is another variation of the time-proportional control system that I described, except that as the batch mass may be different at different times the gain (temperature versus gas flow) would change, leading to possible instability. In addition, controlling pressure is quite a bit more complex, and can lead to interesting burner operation.
 

SamR

Joined Mar 19, 2019
2,134
I have so many alarm bells ringing at this. You are dealing with a flammable gas capable of forming an explosive atmosphere. All electrical and electronics will need to be electrical code compliance verified for explosion-proof rated atmospheres! From the point of fuel supply input line on! This is not something to play around with. Start with the electrical code and work from there. On the gas side you need a regulator to start with. Sizing gas regulators and flow control are typical engineering calculations for a start that require someone with burner management experience. Cutting corners and not dotting the Is and crossing the Ts will void any insurance you may have and leave you exposed to more damages than you can imagine.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Presuming that the TS knows what the temperature profile for roasting is supposed to be, there are controllers available that can provide a string of individually settable setpoints. AND there are temperature controllers available that can continuously follow the temperature setpoint downloaded from a computer, which would be running a coffee roasting temperature profile program.

Adjusting the heating gas flow to hold a temperature for a process is another variation of the time-proportional control system that I described, except that as the batch mass may be different at different times the gain (temperature versus gas flow) would change, leading to possible instability. In addition, controlling pressure is quite a bit more complex, and can lead to interesting burner operation.
The temperature profile you want changes dramatically as a function of batch size, bean origin, freshness, moisture content, etc. As I said before (in the linked post,) I freely admit that useful, effective coffee roasting automation should be *theoretically* possible, however the number of variables (many of them hard to quantify in meaningful units, much less measure without very expensive tools) is pretty high.

An especially fun relationship is centered around the moment when vapor pressure in the beans finally overcomes the strength of the cell walls (there's a fun variable to quantify) which allows the trapped moisture to release in sudden burst, with evaporative cooling suddenly dropping your air temperature readings. Of course, getting that moisture out of the way also opens the door to pyrolysis, so now you're coffee roasting shifts from being an endothermic system to an exothermic system. The result of this is that, right at the moment when your PID controller sees a sudden drop in temperature and wants to apply more heat, it should actually be applying LESS heat.

If you have the resources of Folgers, Starbucks, etc. it might be worth digging into, but for anyone looking at DIY work for a small-to-mid size roasting operation, roast profiling is pure folly.

I've worked with various roast profiling systems, and none of what's publicly available even factors in the moisture content of the beans, which should be a pretty basic one. I'm sure the mega-corps of the coffee world all have their own proprietary systems, but nothing you can buy comes close to doing what you'd really need. You can save and repeat temperature profiles to your heart's content, but you'll be lucky if those settings last you more than a week before you have to create a new profile (manually.) So you might as well roast manually.
 

ebeowulf17

Joined Aug 12, 2014
3,274
I have so many alarm bells ringing at this. You are dealing with a flammable gas capable of forming an explosive atmosphere. All electrical and electronics will need to be electrical code compliance verified for explosion-proof rated atmospheres! From the point of fuel supply input line on! This is not something to play around with. Start with the electrical code and work from there. On the gas side you need a regulator to start with. Sizing gas regulators and flow control are typical engineering calculations for a start that require someone with burner management experience. Cutting corners and not dotting the Is and crossing the Ts will void any insurance you may have and leave you exposed to more damages than you can imagine.
Although I agree with you that a great deal of caution is in order, it sounds to me like the thread starter already has a fully operational roaster with all of the requisite safety features. It's been many years now, so I forget the exact terminology, but I remember clearly that all of the roasters I worked on had to have appropriate pressure regulators, as well as flame control systems that would monitor airflow, incoming gas pressure, and the status of the pilot burner. They would shut the gas off instantaneously if any safety conditions weren't met.

The variable valves with which you drive the roaster are in between the pressure regulator/safety systems and the burners themselves. Nothing you do there defeats any of the safety systems (as long as you don't create a significant gas leak.) So, replacing the manual valves with electronically controlled ones isn't too much of a departure - obviously it's critical that the valves you use be rated for contact with LP at the pressures and flow rates in question, but the thread starter claims to have worked with an engineer to make sure that's done correctly.

As long as the valve is rated correctly, and it's installed without creating leaks, the worst it should be able to do is turn off gas when it didn't mean to - it won't ever be able to turn on gas when the safety prerequisites aren't met. You might ruin a batch of coffee, but you shouldn't hurt anyone or anything.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Yikes! Right after sending my last post, I saw @GetDeviceInfo's post and clicked the link for info on the Clippard valve. That valve is not rated for gas use. The engineer assisting the thread starter apparently cannot be trusted!

I still think there's nothing intrinsically wrong with replacing the manual control valves with electronically controlled valves... but it's incredibly important that you choose the right valves and install them properly!!!
 
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