Works as PID for Electric Smoker?

Hello, I stumbled on this HeaterMeter after some discussion over in the smokinitforums.com forums. I'm considering taking on building this project but I'd like to know if it has potential for adaptation to our needs with the Smoking-It brand of electric smokers (Lazy-Q smokers). We have lots of users (I'm new and looking for better options) on our forum that modify their smokers to utilize the Auber PID Smoker Controller, Dual Probes 1200 watts. These PID Aubers allow up to 6 step programs that can operate based on time or food temps (feedback from probe). The details of this operation are described clearly in the following PDF (pages 2-4):
http://www.smokin-it.com/v/vspfiles/files/AuberSmokinItSimpleIntructions.pdf

These Auber PID's appear to be near the $200 range. So, I would like to know if I can attempt the HeaterMeter project and get it to do essentially the same operations (with cooler features like the wifi enablement, Linkmeter status, and support up to 4 probes) and nearly the same price. It appears the HeaterMeter PID operations are geared at FAN controls for the egg smokers but I wonder how easily this could adapt to something like our Smoking-It smokers using some other accessories like the Solid State Relay (SSR)? If this sounds feasible I think I may take the plunge and try building this project as a community first example for our smokingitforums.com users. I have a computer engineering degree with software experience and some prior hardware "home project" experience but it has been a while since I've done anything like this just for the fun of it.

Looking forward to your feedback and potentially working with some of you in the near future!

Tony

The heatermeter has no concept of a timed cooked, but you could probably replicate that through the use of alarm scripts. It does have the ability to alter the target pit temp based on high & low thresholds being triggered for the pit probe or any of the 3 food probes.

Connected to an SSR, it should do the job just fine.

Yeah timed stuff has always been something I've tossed around doing, but never done. I've never seen BBQ that can be timed, but then again I don't do commercial level quantities. If you just want to change the setpoint based on food temperature, that's easy enough to do with an alarm. If you want multiple steps you can script it.

Connecting an electric smokers is as easy as wiring the blower output to an SSR, setting the "min fan speed" to 100% and the output mode to "pulse". HeaterMeter then runs a long period (10 second) on/off cycle to maintain temperature, suitable for SSRs.

I've used HeaterMeter to drive sous vide heaters, which are similar, as well as in "inverted" mode to power refrigerators so it should work great.

The timing isn't really for the cooking (in most cases). What I typically see is that our electric smoker users doing a ramping temperature profile during the startup phases. The intent of this is to prevent the smoker "belch" condition. The ramping keeps the heating element from getting super hot so fast that it triggers the wood to combust rather than smolder.

Here's a discussion that may better explain (search for ramp if the link don't go right to the applicable discussion):
http://smokinitforums.com/index.php?topic=2583.msg18121#msg18121

Here's an example of a salmon smoke that ramps from 100 (2 hrs) to 150 (2 hrs), and 175 (2 hrs):
http://smokinitforums.com/index.php?topic=2459.msg16904#msg16904

I think I can live without the ramping since I've been using the foil method and it appears to work for me. Or I can experiment with alarms if that's how HM handles trigger events. I think I've reached the conclusion I'm going to order and build a HeaterMeter now. I have a few more questions as I've been reading:

1) Our electric smokers are not rated beyond 350 degrees (at least the model I have). I believe the HM pit probe supports TC but will it work with RTD (Resistance Temperature Detector) probes? I believe most of our users are using the Auber WS-SENSOR11 or WS-SENSOR05 sensors depending on the generation of the Auber they own. If I go with the WS-SENSOR05 I think I could bypass the need for the SMD components on the HM build? Pros/Cons of using this thermistor rather than a TC for my smoker pit probe?

2) For the food probes I think I want to use the Thermoworks probes because of better moisture resistance and temperature range. On the HM probes page I noticed discussion about standard build using 10k resistors but that 22k or 47k can be used to change the probe temperature range? Advantages/Disadvantages of going the non-standard 10k resistor route? I would like ability to have a food probe be a pit probe backup in case something happened to the pit probe and it failed.

3) I seen comments about an RF circuit on the HM (optional I think?). What's this typically used for? Connecting to wireless ambient air sensors like the lacrosse?

Ah I understand about the ramping concept now. I'm wondering if the same effect could be approximated by using the max startup speed in HeaterMeter. You could limit the element to like a 50% duty cycle during startup. I've not tried that to see if the code works but it could potentially alleviate the overheating scenario completely and alleviate the need for more complex time-based profiles. (At least in the belching scenario)

1) No RTDs. HeaterMeter doesn't have the differential circuitry to support RTD probes. Only thermistors or thermocouple and the standard HeaterMeter board can support at most one thermocouple.

2) The advantages are right in the graph. You shift the sensitivity curve. With previous software versions there was a problem where the ET-732 probes would "bounce off" the bottom end somewhere in the 60-70F range so your probes would appear to drop off until they warmed up. The newest software can remedy this to a small degree, and the v4.2 hardware adds filtering to reduce it further. ET-732 probes are rubbish though for their high noise factor and not-quite-right plug lengths so it doesn't make much difference on the Thermoworks.

3) Yes optional. The idea was originally (like 4 years ago!) that you could make a wireless RF transmitter board with your probes in it so it could attach it to a rotisserie and not have the power wire get all tangled up. I've done a couple of reference designs but I think I'm the only person to use it. It also can receive temperatures from some LaCrosse transmitters which is sort of fun to record the outdoor temperature.

Bryan,

Thanks for the response. I thought I read that I would need to configure the HM for 100% min/max fan with the SSR to get SRTP rather than PWM(500Hz). Is 50% duty cycle still possible with this setup for electric smokers? Sorry, I'm new to all this and it's taking me some time to adsorb everything I'm reading. I'm seeking some more clarification on these:

1) The HM appears to have profiles for these Maverick and Thermoworks thermistors. If I went with the Auber WS-SENSOR05 thermistor is there a way to calibrate and make it accurate and usable or am I limited to picking one of the profiled Maverick/Thermoworks thermistors?

2) I'm not planning to use the ET-732 probes. Where I'm located I am hoping to have an HM and sensors that can provide readings in the -20F to 350F range. Should I go with 10k, 22k, 47k resistors on (R5, R16, R17, R18) to best meet this range without "drop off until warm up"? It appears I get better cold performance from the probes moving to higher 22k or 47k resistors. I assume most people use the standard 10k resistors. I'm curious if I would potentially give myself more long term headaches (e.g. noise issues, compatibility, calibration, profiles, etc...) switching away from the 10k standard in the HM build?

3) Does PID autotune exist? know this is an Auber feature and I seen mention of it by you in previous forum posts here but I didn't get far enough in reading to see if it was integrated into the product.

4) Does HM support control cutoff thresholds? For example, if I set a max temp of 350 (detected by any probe or TC) can it shutdown and lockout control outputs to the SSR in hopes of preventing over temp conditions that may cause fire or equipment damage? Or perhaps I should think about better solutions like tightly constrained fuse protection? I've read some stories about some cheap SSR's getting into locked closed rather than open conditions. My smoker contains an 800 watt element (next model up is 1200 watt). I'm thinking I need some fusable protection in the 7/8 Amp ballpark unless I can rely on HM shutdown control logic?

I'm sure I'll have more questions but this is all I can think of after my long night of reading forums last night. Thanks again for the responses!

Tony

I'm not sure about the startup max working with SRTP, I never have tested it. I'll have to look and see if it works but just a brief mental review makes me think it should and if it doesn't, hey, I can fix that.

1) Oh I thought that Auber was an RTD but now I see it is a thermistor. You'd have to figure out the curve coefficients for their probes because there aren't standard values. It isn't as simple as a two point calibration, as you can see the graphs aren't straight lines, they're like triple natural logs. You could ask them for a datasheet and I could do the math :-D Also is that probe connector is too big for the heatermeter, or is it a regular mono jack?

2) Depends completely on your selected probe. 10k was selected to give high accuracy around the 220F mark, but stretch the curve and move it enough to give acceptable accuracy up to around 400F. The higher the resistance the higher the noise, but if you stay in the 10k-220k range I bet it would be fine. You could also put in potentiometers and dial them in. However, there's no guarantee you'll stretch any given curve into any given range, or that if you can the sensitivity won't be bonkers like 2F per ADC tick which will bounce your temp all over the place.

3) No. I have manually tried every autotuning method I could and none of them worked at all so I never have implemented them in code. It is different with an electric element, but a BBQ has so many variables it just doesn't work unless the situation is tightly controlled. I'd rather not implement one then have to try and diagnose why it never works for anyone.

4) No. There's no secondary output to drive a lockout. I have had a cheap SSR lock in the on position and turning off signal to it did nothing, I had to cycle power fully. To do this there would need to be a second output to run a second relay and we don't have that. HeaterMeter will already be at 0 output if you're way far beyond your setpoint so the normal control mechanism won't work.

Ok... well I have ordered all the parts (except the case) and some things have been arriving all week. I'm ready to start some soldering tomorrow. Is there a PDF or printed form of building instructions for a newbie? I can use the wiki instructions but heard people talking about something that normally came with the kit they ordered? I ordered parts since I wanted to build a 4-line LCD version. And man, using Digikey and Newark was rough since the shipping was more than the couple parts I got from them. Sure would be nice if mouser had all the parts!

I heard stories about soldering the SMD parts. I bought a 2in1 soldering SMD rework station cheap from ebay. I hope this makes things a little easier. Anyone use the hot air portion of the station like this to do the SMD soldering? Just apply some solder/flux to the pads, let it cool, apply the SMD component, hold it down with tweezers or something and apply hot air maybe?

I can't wait to see how this turns out!

The sheet that comes with the kit is just a parts list which makes it easier to identify which parts are which because they all come in one big bag. All you parts are in individual bags so I don't know if it would be much help but there are images of the parts sheet on the HeaterMeter Store page.

Thanks... I got things figured out today and built my unit. Unfortunately, I forgot the JP1 socket on my parts order. Now I'm contemplating building a complete second unit since I also have a few leftover parts from my first order here.