# Coffee Roaster - Gas Control Project - Seeking Guidance/Advice

#### MisterBill2

Joined Jan 23, 2018
7,964
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.
The fact that the process, especially for a small organization using variable sources, is why I suggested a fast responding system that can use an external setpoint input. And if the setpoint is controlled by a computer then that same system can have pressure and humidity sensor inputs that the control program can use to determine the required temperature at each instant. And from a safety point of view, solenoid valves for controlling natural gas or propane safely are available already certified. So all of the parts of the system would already be suitable for that sort of application. So the software would be the only part needing to be created for the application.
This means that the users will need to understand just what needs to be happening during the process.

Ron

#### MisterBill2

Joined Jan 23, 2018
7,964
Every now and then the subject of roasting coffee beans comes up. I have to give you credit as there is a science to roasting those little beans.

Using LP gas I believe you really want to control your fuel flow, not the pressure. You come off your supply with a pressure regulator and after that the flame and heat is all about gas flow. Before buying anything I would look to a cheap LP rotometer just to get an idea of what your flow range is. No clue how your burner works mixing air and LPG but either way if you want to control gas flow you need to get a handle on your flow for the process. I would start with a simple, inexpensive roto meter, something under $50 because right now you don't know what flow rates yield what temperatures. Once you have a fuel flow range to work with then worry about control and a decent gas flow sensor. Ron Certainly knowing the das flow could be useful, and just as certainly being able to quickly go between high and low heat settings would be a lot more reliable than any system trying to constantly vary them. Hence my suggestion. #### ebeowulf17 Joined Aug 12, 2014 3,275 The fact that the process, especially for a small organization using variable sources, is why I suggested a fast responding system that can use an external setpoint input. And if the setpoint is controlled by a computer then that same system can have pressure and humidity sensor inputs that the control program can use to determine the required temperature at each instant. And from a safety point of view, solenoid valves for controlling natural gas or propane safely are available already certified. So all of the parts of the system would already be suitable for that sort of application. So the software would be the only part needing to be created for the application. This means that the users will need to understand just what needs to be happening during the process. And the best part is that the whole system will not be so terribly expensive, the temperature controller will be the highest cost item, still below$1000 from Automation Direct.
Again, what you've described with a temperature setpoint controller and a computer control system is a complete automation system which most people (including myself and probably also the thread starter) aren't qualified to set up in a useful way due to the intricacies and hard to quantify aspects of coffee roasting.

The point I'm trying to make is that, if you accept that full automation may not yet be realistic, then in that case controlling based on temperature is much less useful than controlling based on pressure (or perhaps actual gas flow as several have stated.)

Coffee roasting tends to work well with relatively constant rates of heat input for extended periods, with relatively few step changes in that heat input. If you do this in terms of gas pressure (or flow,) then it's quite simple. To try to recreate that same simple behavior with a temperature controller would require gobs of information on complex curves that vary dramatically for every different situation. It's a lot of extra work, and there's no real benefit unless you're actually able to get all the way to the "real" automation system that the big boys have.

As for measuring pressure vs. measuring flow rate, I don't think it makes much difference. Given that you're measuring pressure in a tube of gas immediately before it hits burners with a fixed orifice size, there's a fixed, predictable relationship between pressure and flow rate. Strictly speaking, flow rate may be the more relevant value, but either measurement gives you the same information, since the load (the resistance to flow presented by those burner orifices) never changes. I think roasters gravitate towards thinking in terms of gas pressure simply because many machines have a gas gauge in between the variable valves and the burners for just that purpose. Flow measurement probably does make a little more sense, but I don't think pressure measurement is too bad either.

#### SamR

Joined Mar 19, 2019
3,053
What he needs is a gas burner control system with PID control. Which if it doesn't meet Factory Mutual and NEC standards or the applicable standards for his locale will be an unsafe and uninsurable installation. There are PLC burner management systems available for a price that will allow burn profiles to be stored and used. Honeywell comes to mind.

#### wayneh

Joined Sep 9, 2010
16,767
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?
As I understand it, your chosen valve requires a current controller. Opening position depends on supply current. I guess the driver board converts a PWM signal to a current, but it would be nice to better understand.

You can get a nice PWM signal from just about any microprocessor, and you don't even need a microprocessor. There are myriad PWM-based motor and LED controllers on ebay. Any of them might work here but again, it would be nice to know the details of what you need. Many of those devices actually PWM the power and are not just sending a signal. Your driver board might need only the signal and will translate that to control of the power.

Do you have a pressure sensor selected yet? It will have requirements that might impact your microprocessor choices.

Last edited:

Joined Jan 15, 2015
5,778
Certainly knowing the das flow could be useful, and just as certainly being able to quickly go between high and low heat settings would be a lot more reliable than any system trying to constantly vary them. Hence my suggestion.
I never said anything was wrong with your or anyone else's suggestions. Get that straight. I merely made my own suggestion as to where I would start. Spare me the attitude.

Ron

#### MisterBill2

Joined Jan 23, 2018
7,964
What he needs is a gas burner control system with PID control. Which if it doesn't meet Factory Mutual and NEC standards or the applicable standards for his locale will be an unsafe and uninsurable installation. There are PLC burner management systems available for a price that will allow burn profiles to be stored and used. Honeywell comes to mind.
Automation Direct offers PLCs for a MUCH lower price. In addition, a two-level heating system could use all parts that are already certified for natural gas or whatever fuel is chosen. Meeting all of the applicable safety standards is useful in any legal setup.

#### james211

Joined May 29, 2012
267
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!!!
I've spoken with Clippard directly and they confirmed the valve can be used with flammable gases.

#### james211

Joined May 29, 2012
267
I appreciate all the "interesting" feedback, I have found a very simple solution to this problem per Clippard directly.

#### MisterBill2

Joined Jan 23, 2018
7,964
I appreciate all the "interesting" feedback, I have found a very simple solution to this problem per Clippard directly.
You will often find that some manufacturers are willing to provide assistance in the application of their products. Clippard is one of those. They have a reputation for assisting folks.

#### ebeowulf17

Joined Aug 12, 2014
3,275
I've spoken with Clippard directly and they confirmed the valve can be used with flammable gases.
Well, I apologize if I got that wrong. I am surprised that they say it's ok. I'd expect that to be more clearly indicated. The web listing you shared simply said the medium was "Clean, Dry Air (40 micron filter)"

#### james211

Joined May 29, 2012
267
Well, I apologize if I got that wrong. I am surprised that they say it's ok. I'd expect that to be more clearly indicated. The web listing you shared simply said the medium was "Clean, Dry Air (40 micron filter)"
No need to apologize, you’re not wrong, you read that correctly and I brought that to their attention. The data sheet says it’s fine for gas, but the spec sheet says clean air. That was one of my questions when I spoke with them.

#### GetDeviceInfo

Joined Jun 7, 2009
1,746
Clippard told a company that there was no problem using thier pneumatic cylinders to pump an aqueous solution. Lots of money lost by that company as thier equipment failed in the field. Just saying.

One thing I’m sure you’ve considered is that air volume must change with gas volume.

#### james211

Joined May 29, 2012
267
Clippard told a company that there was no problem using thier pneumatic cylinders to pump an aqueous solution. Lots of money lost by that company as thier equipment failed in the field. Just saying.

One thing I’m sure you’ve considered is that air volume must change with gas volume.
What I can say, is there are several people out there who have been using the EVP valves for several years on coffee roasters without issue, so I feel confident the valve will work fine. Thankfully they aren't crazy expensive either. I appreciate your input.

#### ebeowulf17

Joined Aug 12, 2014
3,275
One thing I’m sure you’ve considered is that air volume must change with gas volume.
I'm curious what you mean by this comment. Coffee roaster burners, like gas grills, ranges, and nearly every other burner I've worked with, use the Venturi effect to draw air into the burner as needed.

Variable valves don't change anything in that regard, so there's nothing to change in the current project as far as air. Besides, every roaster already has variable valves on it - it's just a question of whether they're manual or electronically controlled.

#### james211

Joined May 29, 2012
267
One thing I’m sure you’ve considered is that air volume must change with gas volume.
Not sure if you're referring to air volume for the burners or for the beans, the burners have plenty of airflow and do fine at full 5kPa. As for the beans, they rely on a completely different source of air that is irrelevant to gas power/heat input.

#### MisterBill2

Joined Jan 23, 2018
7,964
No need to apologize, you’re not wrong, you read that correctly and I brought that to their attention. The data sheet says it’s fine for gas, but the spec sheet says clean air. That was one of my questions when I spoke with them.
Regarding the suitability of the valve for controlling fuel gas. My suggestion is to ask what the materials are that contact the gas, and then research the compatibility of that material with whichever fuel gas your system will be using. What the Clippard company tells you and what compatibility charts say may or not differ. I have had sales people tell me whatever tales it took to make a sale, and then discovered later that there was a serious difference. Thus my advice to verify it on your own.