MES 40 - Troubleshoot cause of temp reading on display higher than actual temps

Discussion in 'Electric Smokers' started by hkeiner, Jan 20, 2011.

  1. sigmo

    sigmo Smoking Fanatic

    After reading all of the posts about the accuracy of the controller's temperature indications in the MES40, I decided I should perform what I consider to be a good test of mine.

    I just got this unit, it's a 2011 model, purchased just a few days ago at Sam's Club.  (They do not have the newer version at Sam's yet).

    I did this testing last night, so pardon the pictures all taken with flash between midnight and about 03:00.

    First, I was incorrect in my recollection of the location of the sensor in my smoker.  It's actually positioned quite low in the cabinet, and pretty much right above the heating elements.  The overtemperature cut-off "snap-disk" control, however, is located higher, and to the left as shown here:

    [​IMG]

    I sometimes see the controller temperature sensors for lab ovens located very near the "outlet" of the heater.  I believe this is done to make it easier to "tune" the controllers for good stability (low or no "ringing and overshoot", but doing this comes at the expense of overall accuracy of the control system because the sensor sees the output of the heater, and thus, underestimates the temperature in the main body of the cabinet.  However, this may also be seen as a benefit because it assures that no part of the cabinet will ever be driven above the setpoint.

    This may be the same strategy that MB has used here.  They may feel that it's more "conservative" or "safe" to set things up so that there will be no areas in the smoker that are ever much above the selected setpoint.  But this does mean that other areas may be quite a bit cooler than what the controller "thinks" they are.

    As I've pointed out in other posts, you will be very surprised at the variations in temperature between different locations in a typical oven or incubator, even a laboratory incubator or oven.

    Regardless of all of that, the question in my mind was:  Does the temperature controller in my smoker read accurately?

    I had questioned the readings people were getting and posting in this thread and others because my experience with this sort of thing has taught me that to test any temperature sensor, you must be certain that the sensor under test is really at the temperature you think it is at.  To know this, you must have a way to thermally couple the sensor under test to the reference sensor.  Only if they're both known to be at the same temperature can you draw any valid conclusions.  And this is not as easily done as one might guess.  Just having a probe within a few inches of another probe, in air, can mean very little.  I often measure differences of 20 degrees C or more in "good" ovens with probes that are only a few inches apart.  It's particularly noticeable when you have no active stirring of the air (by a fan or blower).  But you will even find variations that are annoying in incubators or ovens that ARE stirred by fans.  It's a constant source of concern in a laboratory environment where tolerances are tight.

    Anyhow, while variations in temperature within a smoker are, of course, a great concern, I'm not addressing that here, except to point out that just putting a probe into the smoker and comparing what it reads against what the smoker's controller reads will always be an exercise in frustration and won't tell us if the smoker's probe/controller is accurate.  We haven't controlled all of the variables, so it's not a valid scientific experiment.

    OK, so I wanted to make my testing BE valid.

    To that end, I did the following:

    First, I found a temperature probe that was very tiny and had a cable on it that was small in diameter so I could just slam it in the door of the smoker.  Then I tested the calibration of this probe and its readout to make sure it was accurate.

    I used a dry-block calibrator that I built a few years ago for the purpose of calibrating thermometers and electronic sensors.  Basically, it consists of a large piece of machined aluminum that is surrounded by a "band heater'.  The heater is controlled by a little PID controller and solid state relay.  That controller reads a platinum RTD that is embedded into the aluminum block from the bottom, very near the bottoms of all of the various "wells" in the block.  That whole assembly is mounted to two sheets of teflon to provide thermal insulation along with mechanical stability.  Then all of that is surrounded by fiberglass insulation so the heater will not need to work hard once the block is up to temperature.  The block is big and massive, and well insulated, so it has a long thermal time constant.  The aluminum is a good thermal conductor so that, at least when the temperature of the system is not changing much, the temperature throughout the block should be quite uniform.  It won't be perfect, but it's darn good!

    The idea is that I can place electronic probes into various "wells" in the block, and know that they're all going to be at pretty much the same temperature.  There is also a central well that I can fill with thermal oil for testing liquid-in-glass thermometers or odd-sized/shaped electronic probes.

    I use a precise electronic calibration thermometer as the "transfer standard" to compare against the sensor(s) under test.  That reference calibration thermometer system is calibrated and certified annually and the certification is NIST traceable.  It's rated to be within + or - 0.015 degrees C from -50 to +200 °C.

    I used this setup to test the thermocouple probe/readout system before using that thermocouple/readout system to test the smoker's probe/controller.

    [​IMG]

    [​IMG]

    It was good enough.  I tested it at room temperature, too, and it was dead-on.  Great!

    Then, at home, I attached the tiny thermocouple to the smoker's sensor:

    [​IMG]   [​IMG]

    I just held it up against the smoker's sensor and wrapped that all up with a strand of tinned copper wire to get the two in good contact.

    Then I wrapped all of that up in aluminum foil.  The idea was to make sure that both sensors "see" the same temperature at the same time.

    [​IMG]

    It looks crude and ugly, but it ought to do the job well enough.

    [​IMG]

    I had enough wire on the thermocouple to reach up out of the smoker, but just barely.  :)

    So I shut the smoker's door and started testing.  I first checked at the ambient temperature, and was pleased to see that both systems agreed well enough:

    [​IMG]

    But then, as I increased the temperature, what I found was kind of strange.  The sensor/controller is quite non-linear.

    I allowed the temperature to overshoot the setpoint and then settle slowly down so that I had the lowest possible rate of change of the temperature in the smoker when making the comparison readings.  The lower the rate of change, the less likely issues with the thermal time-constants of the two sensors will cause errors.  We know that the tiny thermocouple I attached to the outside of the smoker's probe will react more quickly than the sensor within the smoker's probe can because there must be some "insulation" between the smoker's probe's sensor and the outer body of the probe itself.  So if the temperature is rising or falling rapidly, there will be a time lag between what my tiny thermocouple sees and what the sensor inside the smoker's probe will see.

    Anyhow, when things were reasonably stable at any given temperature, that's when I took a picture to record the temperature readings.

    Here's what I got:

    Reference Thermometer Reading ----- Smoker Controller Reading

    66.8 ----- 66

    100.9 ----- 97

    131.5 ----- 145

    150.3 ----- 166

    191.6 ----- 203

    245 ----- 262

    262 ----- 280

    At room temperature, the smoker and reference agreed.

    At 100 degrees, the smoker read a bit low.

    Then, at all temperatures above that, the smoker read considerably higher than the reference system.

    This agrees with what I think most other people have reported here.

    If the controller and its sensor were meant to accurately display what the sensor is actually seeing, then the design or implementation is fairly poor.  It's pretty easy to make an electronic thermometer that is quite accurate without spending much money, particularly if you already have a microcontroller at your disposal.  And we know they do because the system has a remote control.

    But to give MB the benefit of the doubt, it's possible that they intentionally bias the readings at different temperatures to compensate for what they believe the actual average smoker temperature will be at those temperatures with typical meat loading, etc.  Who knows?

    I have not taken things apart to see what kind of temperature sensor is used.  It could be a thermistor, RTD, or thermocouple.  Thermocouples are cheap, rugged, and stand up to a wide range of temperatures.  But they require either a rather baroque analog circuit to "read" them, or a microcontroller programmed to perform the calculations using the multi-order polynomial expression that relates their voltage output to their temperature.  Further, you need another temperature sensor to compensate for the thermoelectric voltage generated at the "cold junction".  This is actually easily done with modern sensor ICs and a microcontroller.  Analog Devices (and maybe others) make ICs specifically meant to "read" thermocouples, so using one of those can provide an easy solution.  But if all of this isn't done properly, you'll get bizarre readings from a thermocouple.  They're non-linear and there will be an unpredictable offset generated by the cold junction connection.

    Thermistors sometimes require compensation for their non-linearities, but that can be done very successfully, too, with the right circuit or controller programming.

    RTDs are excellent, and again can be read very accurately if things are done correctly.

    Semiconductor temperature sensors can be great, but normally won't handle the high temperatures we'd require for a smoker controller probe.

    So the real questions I have now are:

    Do we really care about the inaccuracies we're seeing in the MB smoker's sensor/controller system?

    Are those "errors" actually carefully programmed adjustments meant to compensate for the probe's position in the smoker, and they actually make the system more accurate?  Or are these errors really just errors that we should try to "fix"?

    The thing I like about the MB system is the remote control/readout.  I really do like being able to check the temperatures without leaving my easy chair (or even bed) when doing a long smoking.

    I could easily install a different probe and a good PID controller.  You can get PID controllers off of EBAY for amazingly cheap.  I haven't tried any of them, but even from Omega, I can get a very good PID controller for under $100.  A solid state relay and a heatsink, some wiring, a sensor, and you've got it all done.  Going the high-dollar route, you might have $150 into the mod.  Shopping on EBAY for a cheap PID controller, you could probably do the job for under $50 for everything.

    But you'd lose the remote control feature (not the readout).  That might be perfectly acceptable.  You could wire things so that the remote control could switch the whole thing on and off and still read their sensors, but you'd have to set the temperature on the new controller.  That wouldn't be so bad!  And many PID controllers will do "ramp and soak" which would let you program a routine of different temperatures at different times with "ramping" of the temperature to your desires.

    The problem with any proportional control is that you WOULD need a separate smoke generator because with the heater properly proportioned, the temperature of the heating element would often be too low to make the chips smolder.  The advantage of the factory system is that it does cycle the heater on and off, with quite a bit of hysteresis, so that when it comes on, it comes on for long enough to heat up the chip pan and make them smoke.

    But I still wonder if there is a method to MB's madness with the apparently crazy non-linearity of their system.  Maybe it is meant to compensate for something.  I kind of doubt it, but who knows?  I wonder what MB has to say about this?

    Maybe the point is simply that there are other variables that will render things to be so inaccurate anyhow, that the controller/sensor errors are small in comparison.

    The pork butt that I smoked in mine came out fine.  And the internal temperature did what I expected it to do for the smoker temperatures I thought I was getting.

    Next, I suppose I should check the probe sensor and its readings! 

    If you've read this far, you're either really into this, or a glutton for punishment (as well as smoked meat).  Sorry for the long post.
     
    texacajun and overground like this.
  2. rabbithutch

    rabbithutch Master of the Pit OTBS Member SMF Premier Member

    Howdy Sigmo!

    You just KEEP ON adding good advice and content to this forum. Thank you!

    You seem to be very expert in measuring temperatures (and you're and MES owner); so I'm going to ask you about what to do when the sensor stops the heating element from getting power at 275* if you can't get your meat to the desired IT? It's that upper limit cut-off that can be a killer if the sensor is bad or placed badly or whatever, and stops the heat.

    Got any hints or work-arounds that would be safe but would also get the job done?
     
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

     RH, evening.....  Exceeding the limit cut off temp, as it is pre set, could damage electronics that are hidden in other areas of the smoker....  Every smoker has a learning curve that takes time to adapt to...

    Dave
     
  4. sigmo

    sigmo Smoking Fanatic

    Hi there.

    Last night, I tested my MES40.  Earlier today, I posted a long-winded description of what I did and what I found.  The post is very picture-heavy (I do like photography). [​IMG]   I think that because there were a lot of pictures in the post, and I'm new here, that post has been side-tracked for human scrutiny (moderation) before it will show up in the forum.

    The short version is that I used a proven-accurate meter with a tiny thermocouple probe, and attached that little probe to the MES's controller probe so that I could be reasonably sure that the two probes would always be "seeing" the same temperature.    I then set the MES for 100, 150, 200, 250, and 275 degrees and noted the readings from the MES's controller and the reference thermometer.

    As it turns out, my MES's controller is quite accurate at 68 degrees, reads a bit low at 100 degrees, then suddenly begins to read 15 to 20 degrees high when it gets up to about 135 degrees!  Quite strange.

    I won't re-hash everything I said in the other post, because I'm hoping it will show up here before too long.

    I also won't put any pictures in this post because it seems as though including photos triggers the mandatory moderation of the posts.

    To your question:  If the inaccuracy of the controller/probe in our MESes prevents us from being able to actually achieve a temperature of 275 in the smoker, the best thing would be to somehow adjust or cheat the controller into making a more accurate measurement.  That would maintain all functionality and safety built into the smokers.

    Hopefully, the little snap-disk overtemperature limit switches are not the problem in any of these MESes.  If they are, they could be replaced with more accurate ones, but I suspect those are OK.  The snap-disk limit switches are the safety limit in these cookers.  They're really not meant to control the temperature, but rather to shut off power to the heater if the unit gets over some temperature that MB has determined is a safe upper limit.  It looks like they use some type of foam insulation in the units, and that probably has a fairly low upper working temperature.  So we do need to be sure not to get things too hot in there. 

    So assuming the problem is with the controller/probe, we then need to understand what's creating that error.  It's interesting that a lot of us seem to have systems where the controller reads too high, but at least one (and probably more) people have units where the controller reads too low.

    But again, I caution everyone that its not trivial to make valid tests/comparisons.  So we do need to be sure the measurements are all made properly before we jump to any conclusions.

    I need to take the unit apart, make some measurements, and take a close look at the controller's circuit board to try to figure out what kind of sensors the system uses and see if I can figure out parts of the circuit that does the measurement of the probes.  It may be that there is already an adjustment on the board.  It may be that we could add an adjustment.

    It also may be, as I speculated in the other post, that there is a method to MB's madness, and they intentionally skew the readings from the sensor in order to achieve better real accuracy out in the main area of the smoker.  The shape of the "curve" of the error in my smoker is pretty strange.  And they've got a microcontroller at their disposal, so it would not be difficult (or expensive) for them to make it quite accurate - if that's what they want.
     

    I'm going to check to see if my other post has made it through yet.  [​IMG]

    Edit to add:  It did.  It's up above this, as post #21. 
     
    Last edited: Jun 6, 2012
  5. This is just a shot in the dark but after looking at you photos I have a half smoked theory.  Would different ammounts of contact between the sensor and the material the internal walls are made of cause the wild differences we see between everybodys MES's?  Essentially the probe is coupled to the internal wall if it is touching it correct?  Maybe insulating the probe from the wall ,ie. routing the hole out a few mils, would provide better accuracy.
     
  6. sigmo

    sigmo Smoking Fanatic

    That is a good observation, and something that does need to be considered when one designs a temperature measuring or control system.  There's a whole science of designing what they call "thermowells" for use getting measurements where the sensor needs to protrude into a pipe or chamber.

    Ideally, the way a probe of this nature is built, the actual sensor is placed as near to the end of the probe housing as possible, or even touching it.  The sensing should be happening right out near the tip of the probe housing.

    The sheaths are usually stainless steel tubes that have been spun closed and TIG welded at the end, then ground to form a nice, smooth tip.  Inside, it's just a closed-off tube and it might be a bit thicker right at the tip, but hopefully not too much thicker, so the actual sensing element can still be placed fairly close to the tip we see from the outside.

    Stainless steel is only a fair conductor of heat.   So ideally, the thermal conduction down the length of the tube is fairly low compared to the conduction straight through the walls of the tube to the sensor element.  It's always hoped that the contact you're talking about will have a minimal effect.  But I agree that MB has kept the probe penetration into the smoker quite short, and the conductivity of air to the probe is a lot lower than the conductivity of steel to steel at the hole you're talking about.

    Normally, when I set something like this up, I opt for a LOT more penetration.  Sometimes the probe manufacturers will recommend some number of probe diameters of protrusion into the area being measured, and this will be different for air than, say, water.  Air being the worst conductor of heat, and requiring the deepest penetration to avoid "wall-effect".  But I suspect that MB wanted to keep the probe stubby to avoid people ending up with it touching some meat or being knocked around and bent or broken off easily.  So it's a difficult tradeoff.  I'd have gone with a probe sticking in at least two inches.  But then I'd have to be very careful not to damage it whenever working inside the smoker.  I suspect MB doesn't want any more service calls than they have to have, so mechanical strength trumps ideal sensing in this case.

    However, we also hope that the inside walls of the smoker are close to the smoker air temperature due to the insulation being pretty good, too.  And it may be felt that really, the wall area around the probe is just as legitimate of a "sensor position" as the probe itself.  So if it picks up some wall influence, that may be just fine, or even a design feature that's been calculated into the whole overall design.

    But your concern is really the consistency of this coupling from the wall to the probe from one person's smoker to the next.  And that's a legitimate issue.  But:

    If we open the hole a bit, the bracket that mounts the probe (probably part of the probe itself - welded to it right behind the wall) would still be in very good contact with the probe and the wall, so right behind the wall, we've got a bracket with excellent contact to the probe anyhow.  That would tend to make all of the units behave about the same by tying the probes thermally to the walls in a fairly consistent way.

    When I did my experiment, the tiny thermocouple I used should have tracked the temperature of the smoker's probe, right about where the sensor should be inside of the probe.  Because of the tiny mass of my probe and how it was coupled to the sheath of the smoker's probe, what I ended up measuring with my little thermocouple should have been the temperature of the smoker's probe's sheath.  (I hope that makes sense).

    So, what I set out to do was to see if the smoker's probe/controller system was reporting the actual temperature of the smoker's probe.  This completely ignores the issue you've brought up of whether or not the probe "sees" the air temperature in the smoker.  My experiment, hopefully, reduced the variables to only the one I was interested in testing.  In a sense, I didn't care, for the purposes of this one experiment, whether the probe was properly designed or mounted.  [​IMG]

    That doesn't mean that we should ignore all of that, however!  It really is important.

    BUT, the thing I was testing, and what I found with mine, was that the smoker's probe/controller doesn't even properly report the probe's temperature.  Nevermind that the probe may not be designed or mounted ideally, it doesn't even report its own actual temperature accurately.

    For me, the starting point has to be that the probe/readout system has to be accurate in and of itself.  Then you have to worry about positioning it properly and, as you point out, making sure that the design of the probe and how it mounts assures that you're reading what you want to read (in this case, the smoker's internal air temperature).

    BUT, again, you make a good point about just trying to explain the differences we see reported by different people for different smokers.

    I haven't taken the back off of the smoker to see what the back end of the probe looks like, but based on the screw we see right next to the probe, I'm guessing that what we'd see is that the probe tube pokes through, and is welded to, a flat steel bracket.  That bracket has another hole in it for the screw to grab.  So even if the probe hole is not touching the probe the same way in everyone's smokers, the flat surface of the brackets are tightly clamped to the back wall of the smoker in every case, so we probably get about the same conduction of heat from the smoker's back wall to the probe tube in every smoker - if you see what I'm getting at.

    I tend to suspect two possible other reasons for the discrepancies we see from person to person/smoker to smoker.

    First, just us measuring things differently.  If everyone did the experiment exactly the same way, we would eliminate that very large potential error.  But we know we haven't, so we haven't eliminated all of the other variables, so we don't have a valid scientific experiment.  Instead, we've got a lot of anecdotal reports where everyone has done things their own, different way.

    Second, I would not be surprised to find that there are some wacky inconsistencies in the controllers or the sensors MB has used.  There really may be the kind of varying errors that have been reported!

    So I think you've got a good point about whether the probes are really measuring what we wish they were measuring (air temp only, with no "wall temp" influence).  But I think that they may all be doing about the same thing in that regard due to the bracket factor.  But again, I have not looked inside the back to know exactly how they are built, so you can take my thoughts on the matter with a big grain of smoked sea salt!  [​IMG]
     
    texacajun likes this.
  7. justint

    justint Newbie

    Good. So this correlates fairly well with my initial findings. I doubt it if MB intentionally bias anything. Personally I don't believe we can expect better from smokers at this price point but they could have made it far more usable at no extra cost. If they read this, may be 2013 model.

    The 2nd time I cooked with the 2012 MES30 I recorded the following (from 4 probes)

    ThermoWorks meat probe/ MES meat probe, ThermoWorks oven/MES set temperature

    55, all 4 probes read  to within ½ degrees

    76/82 (delta = 6 degrees), 228/265

    109/120 (delta =  11 degrees),  235/270

    133/154 (delta =  21 degrees)

    I trusted the TW probes and cooked accordingly. MB could have chosen to calibrate at a higher point more relevant to cooking temperatures, like at 133. Who cares if it’s accurate at 55 degrees.

    Below are the probes I used . The ceramic fiber probe is flexible so can be looped through rack and positioned near meat.

    For meat probe:

    “Thermoworks Smoke House Penetration Probe - Stainless Armour Model: 113-178

    Penetration probe used by commercial smokehouses.

    Accuracy: ±0.9°F (±0.5°C) from 32 to 212°F (0 to 100°C) “

    For oven temperature – positioned about 2-3 inches from meat

    “High Temp Flexible Ceramic Fiber-Insulated Probe

    Model: WD-08467-64/WD-08467-64-10

    The High Temp Flexible Ceramic Fiber Insulated Probe is used in commercial ovens and furnaces.

    Accuracy: ±0.9°F (±0.5°C) from 32 to 212°F (0 to 100°C) “

    Monitoring is via the Two-Channel Thermocouple Thermometer with Alarm #TW8060. Set to alarm at meat probe temperature of 133F (medium rare).

    The 2012 model is also limited to 275F setting which means substantially lower max oven temps. Calibrating at 133 would have helped substantially. Of course mine is now calibrated at a couple of points, I just have to mentally add the difference.
     
  8. sigmo

    sigmo Smoking Fanatic

    I agree that the errors we're seeing in the MB's temperature control probes is probably unintentional.  But it is amazing to find them so far off when it's so easy to make them be very close.

    This all got me wondering about the accuracy of the meat probe in the unit, so I did some testing tonight on mine.

    Reference Thermometer ----- MasterBuilt's Meat Probe

    100.003 ----- 100

    126.009 ----- 127

    149.855 ----- 151

    175.293 ----- 177

    200.015 ----- 202

    So the meat probe in the MB 40 is plenty close enough for my purposes.  And that adds to the question of why the smoker's temperature control probe would read so far off.  If they can get the meat probe to be fairly accurate, why not the temperature control sensor?  It sure seems like they'd use the same type of sensor so that their controller circuitry would only need to deal with one type of sensor input.

    At least I can count on the smoker's meat probe to tell me when various meats are really at the correct internal temperatures.  That's important for food safety.

    I also tested a few other cooking thermometers while I was at it.

    [​IMG]

    [​IMG]

    [​IMG]

    The reference thermometer's probe and the little Thermoworks meat thermometer were inserted into the dry-block's dry wells while the probes for the two wired-remote probe alarm type thermometers and the probe for the smoker were all inserted down into the center well which was filled with cooking oil.  I should have gotten a better picture showing how it looks down in there.  It's just a way to thermally couple everything reasonably well.
     
  9. rabbithutch

    rabbithutch Master of the Pit OTBS Member SMF Premier Member

    Congratulations on another, most excellent post, Sigmo!

    Thank you!

    Referencing your results, you say that the calibrating sensor reading 262* produced a reading on the MES of 280*. Is that correct?

    You then point out that the "snap-disk" sensor is designed only to stop power to the heating element when its upper limit is reached (which makes a great deal of sense). I have been guilty of broad jump logic by assuming that the heating element was turned off by that "snap-disk" sensor. If I've followed you correctly so far, I must ask how you account for getting a reading on the built-in heat sensor of 280* if that is the part that is controlling the heating element. Of course, this might be due to some incremental heating that occurred in the air after the sensor reached 275* and shut down power to the heater element. We don't know. I think your test results confirm my concerns, and perhaps those of others, about the temperature sensor and how it controls the heating element. Suppose, for example, that any 2 MES units of the same model might have sensors that vary by as much as 10%, but that the electronics are constant in their treatment of the signals. My hypothesis is based on an expectation that there is far less variance in the electronic circuits than between sensor units. (This is a totally uninformed, uneducated guess). Given those conditions, then it might be possible that my MES sensor reads 10% lower than the one you tested at the same ambient smoker temp giving me a reading of 288*. This means - assuming the electronics shut power to the heating element when the sensor crosses the 275* threshold - that additional heat would have been stopped at 249* while reading 288*.

    That is, admittedly, a rather convoluted argument and assumes far too may constants, but I was trying to reconcile observations I've made while using my MES40. You point out that air is far from the best medium by which to compare readings of different probes. I defer to your much greater expertise in this matter and have no doubt it is true, but it is hard for me to reconcile a difference between the chamber sensor reading of my ET-73 of 245* and a reading on the MES of 279* while observing that the element heating light is not lit. Combine a few of those readings with unintended shut downs due to my hitting the remote on/off button and not being aware that an upper limit set too low will shut heat off, and you have meat probe temps that stall or drop. This is vexing, to say the least. Yes, much of the damage was self-inflicted. I'm learning but CRS is a constant companion at my age. I'm unaccustomed to having similar problems in kitchen oven because one doesn't set both lower and upper limits and one doesn't risk turning one off with the remote. It is these conditions that cause me to be dissatisfied with the electronic controls and sensors on the MES. They may or may not suffer from defects and or quality control issues, but I contend that the electronics should display information more readily understood by anyone standing within 1/2 SD of the apex of the IQ bell shaped curve. The frustration comes from the knowledge that the technology exists and that incremental production costs would be nil. It seems to be that only the R&D costs for connecting the IC's and other components are the problem. Those costs, amortized on large numbers of units sold must also be relatively insignificant.

    Sorry for being so long-winded, but this subject - and your ability and willingness to run the experiments for us - will help all of us become better smokers and might even help MB produce better products in future. If you need a challenge for future experimentation, I suggest that you track sensor readings against a calibration standard sensor and record the points at which the heating element is powered. I would really like to know to what temperature it will continue to heat with my upper temp setting at maximum.

    Thanks again for such excellent contributions here! Thumbs UpThumbs Up
     
  10. Excellent information. I previously thought the primary reason for the disparity between my MES's temperature reading and my Maverick's temperature reading was due mostly to the different  locations of the probes. That is, the temp along the back wall just above the element (where the MES probe is located) was that much higher than the temperature on the middle rack (where the Maverick probe was located) due to the different thermal/radiant heat conditions between these two locations. This explains why my previous attempts to compensate for this (by placing heat shields such tiles, aluminum foil, deflectors, etc along the back right corner of the MES) had limited success in reducing this disparity. I am still very happy with my MES anyway, as all I need to do is set the MES about 20 degrees higher than the desired temperatue and then monitor temps using the Maverick.
     
    Last edited: Jun 11, 2012
  11. sigmo

    sigmo Smoking Fanatic

    Here is the thing I probably have not explained well enough:

    The snap-disk temperature switch is a "last ditch" or "emergency" shut down device. It is wired in series with the heating element AND the power relay that actually controls the heater.

    Effectively, there are TWO devices that can control the power to the heating element.

    This is commonly done to provide safety in heating appliances.  The snap-disk is not normally the part that will control the smoker's temperature (but it can in an emergency).  Instead, it's there just in case the sensor goes bad, the controller goes wild, or the power relay's contacts weld closed (or, if it's a solid state relay, it breaks down and shorts - triacs and SCRs tend to fail shorted).

    In any of those scenarios, the heating element would be powered on "solid" and the temperature in the smoker would climb uncontrollably.  In such a situation, when the snap-disk reaches its cut-out temperature, it would open the circuit and kill power to the heater.  Snap disks can be bought with various "cut in" and "cut out" temperatures.  They often have a very wide temperature gap between their cut in and cut out temperatures.  But in this case, we don't care.  It's just meant to prevent a runaway and keep the smoker from burning itself up.  I think the insulation in these smokers may be one of the things that they worry about if things were to get too hot.

    So under normal operation, we'll never see that snap disk do anything.  It's just a constantly closed switch in series with the heating element that's there in case of dire overheating.  Then it'll pop open and keep the smoker from damaging itself or burning up.  I have not had the cover off of the smoker, so I have not looked at the back side of that snap disk, and don't know for what temperature it is rated.  They're usually marked, and even if the number doesn't directly tell you, you can look up that model of switch and see what the specs are.  I'm guessing, maybe, (speculating, actually) that they're chosen to trip off at, perhaps, 350 degrees or something.  That way, they won't trip unnecessarily, but they will stop the smoker from catching on fire.  :)

    So, under normal operating conditions, that snap disk doesn't enter into the control picture.

    Instead, the smoker's electronic controller switches the power on and off to the heating element based on what it reads from that slender little probe sticking into the back of the unit down lower.

    What I tested was the relationship between that little probe's actual temperature and the reading we see on the smoker's controller.  When that sensor was at a real temperature of 262, the display on the smoker's controller was showing 280.

    From observing mine, the smoker puts full power onto the heater until the display on the smoker reaches the temperature I've set it for.  Then the power to the heater is switched off immediately.  The temperature will then "coast" upwards beyond that point because of the thermal energy stored in that red-hot heating element.  We call this "overshoot" in control systems.

    I haven't studied exactly when the heater is turned on, as the temperature read by the controller drops down below the setpoint, but I think they just switch it on as soon as the display reads anything below the setting.  I'll check that out sometime.  Often, in a control system, you'll build in some "hysteresis".  A purposeful difference between the trip-on point and the trip-off point.  That hysteresis prevents the heater or cooler from cycling on and off too quickly.  Rapid cycling wears out control relays (in the case of a non-solid-state relay) and in a chiller situation, it'll wreck the chiller's compressor.  So sometimes we'll build in a fairly wide hysteresis  or "dead band" to limit how fast things can cycle.

    This type of operation is usually called "bang-bang" control.  The heater is either fully on or fully off.  And you get temperature cycling as a result of the stored energy in the heating element carrying the smoker's temperature above the setpoint every time the heater is switched off by the controller even if they have NO hysteresis built into the controller.  There's nothing really wrong with this.  Almost all ovens do this.  Things don't need to be all that perfect to still work OK.

    Better would be a proportional control for the heater, but if you had that, the heating element would almost never get hot enough to make the wood chips smoke.  This is one of the design tradeoffs that they must make for this design of smoker.  You want decent temperature control in the chamber, but you've also got to assure that you really put the heat to the smoking chips every so often to keep them smoking.  With a proportional control, you would throttle the power to the heater continuously so that it'd run at a low power all of the time.  That exact power level would be maintained "proportional" to the error between the actual chamber temperature and the setpoint.  The farther below the setpoint the temperature read by the sensor, the more power would be applied to the heater.  So when things reach a steady temperature just below the setpoint, the power to the heater would be fairly constant, and presumably fairly low.  So you wouldn't get any smoke except right at the first of the run when the heater runs at full power for a short time to get the smoker up to near the setpoint you've set.

    So they actually rely on the hysteresis or temperature cycling of the chamber to get some smoke now and then as the controller switches the power on each time.  You almost need to have bad insulation in the cabinet to enhance the smoke generation.  This is why one of the aftermarket smoke generators seems like such a good idea to me, and I've got an Amazin unit on order myself!

    OK, that's getting a bit off track from your questions, I guess, but it's important in analyzing why MB does things the way they do.

    Your concern about the accuracy of the sensors and/or electronic controllers is a very valid one.  Sensors can be inaccurate and have wild variations from one example to the next of the same make and model.  But sometimes, they're actually very good so that they can be substituted for each other in some systems without any need for calibration of the system.

    The electronics, likewise, can be made to be very accurate "right out of the box" OR they can be made with parts that have a very loose tolerance, and thus require some type of calibration to get things right.  In the past, electronics that needed to be very accurate were made with tight-tolerance parts and then had an adjustment of some sort to tweak things in.  Newer designs often use good tolerance parts, but leave out the manual potentiometer or other "hand" adjustment because hand-adjusting things requires (usually) human time and labor, and that's expensive.  So lots of modern electronic controls are adjusted automatically by changing stored data used by a microprocessor or microcontroller.  That allows for easier automation of the adjustment process.  Or the tolerances of the voltage references and other components are just so good that for normal use, no adjustment is required.

    These MESs are kind of disappointing.  It seems that they're not very accurate for whatever reason.  I have not had the controller apart.  I just put my smoker together and started using it right away.  I will take it apart and see what I can find out from looking at things.  I would not make any guess as to whether the controllers or the probes are to blame for the strange deviations we're seeing in these units.

    Further, the fact that the meat probe on mine is so accurate while the smoker temperature probe seems to be so far off (and non-linear) is mysterious, too.  If they can get it right for one of the probes, why not for both?  They're both important.

    When you get a reading of 279° on the MES display while your ET-73 shows 245°, it's possible that you're seeing two things at once.

    First, your smoker's sensor and electronics might be almost exactly like mine, reading about 18-20° higher than what the probe is actually experiencing.  Then second, you may also be seeing exactly what you've described where the temperature of the smoker's probe, being right above the heating element, IS seeing a falsely high temperature that is not representative of the temperature elsewhere in the smoker chamber.  Then again, your smoker's probe/controller might be off farther than mine is!

    And, you'd see this worst-case discrepancy for the time right after the smoker's heater has just been shut off by the controller.  Say the controller switches the heater off right when it crosses the 275° threshold.  But there's still a lot of residual heat stored in the heating element.  The temperature seen by the smoker's probe will continue to "coast" upwards, (overshooting the setpoint).  And that's the time when you'll see this very high temperature reported by the MES controller, but your good thermometer, placed elsewhere, may be seeing the "real" temperature in the main area of the chamber so now you've got that wild difference.

    If the smoker's controller actually displayed, and controlled based on, the REAL temperature of the little probe, I would not be all that concerned about reading lower temperatures elsewhere in the cabinet.  I'd chalk that up to the design of the system, and figure it was OK for that to be observed because the manufacturer was trying to be conservative and prevent the smoker from ever being a lot hotter than it ought to be, even in areas closer to the heating element.  There will always be some differences in temperature from place to place in the smoker.  And with a probe near some meat, it may read quite a bit lower because the meat itself is cooling the air next to it as it absorbs the heat energy from that air.  That's always going to be the case in any oven or smoker.

    A convection oven (oddly named IMO because they do NOT rely on convection, but instead on forced air flow) would be a lot different.  The forced air would be closer in temperature from place to place in the oven.  Still not perfect, but closer.  It'll also cook a lot faster for any given temperature because of this.  The air temperature right at the meat will be close to the actual oven setting, so the meat is really "seeing" a much higher temperature in a convection oven than it would in a "regular" oven set to that same temperature.  This is all normal and expected, and it's why you shouldn't get too upset when you measure temperatures, with a separate probe, near some wet, cooking meat, that is lower than the oven's set temperature.

    But again, what I measured in my MES was a discrepancy between the oven probe's temperature and the temperature displayed on the controller.  I don't like that at all.

    Maybe I can find a way to make an adjustment in the electronics or in the probe's wiring to dial things in better.  But the non-linearity is concerning.

    Also, if people's MESs behave the way ours do, then we cannot actually get the ovens up to 275°.  The highest I figure I can achieve will be about 257°, and that's not counting the effect of the probe being right above the heater.  Still, it would make me happy if the controller simply reported the actual temperature of the probe - to within a few degrees, anyhow.

    I'll certainly report back here if I take things apart and learn any about what kind of sensor they're using and what, if anything, we can do to adjust things better.
    I do think the probe positions will greatly affect what we read.  So your thinking has been right.  But it also appears that (mine at least) also just reads too high for what the probe is actually seeing.

    The problem with setting things about 20° above what you really want would be if you do want to cook at a temperature of 275.  We really can't ever get that if all of our units are reading 20° too high.

    I wonder if they're all about the same amount off, or if it varies a lot.  I'd love to have more data, collected by thermally coupling our "reference thermometers" directly to the MES's probes.

    If they're all off the same way, and given how good my MES's meat probe seems to be, then it makes me wonder even more if the "errors" we're seeing aren't being done on purpose.  It doesn't seem right.  I would like to know what a bunch of other people see when they couple their MES control probe to a known-good thermometer.

    Maybe I'll swipe the controller back off of the top of my MES and take a look inside of it tonight.
     
  12.  I get similar results to what you get when I place a known accurate thermometer probe near the cabinet probe in my MES40. The cabinet probe reads about 20 degrees warmer then the other thermometer when I'm cooking at about 225. I have to set my controller at 245 to get the temperature I'm after.

     I anxiously await any further information you come up with.

     Chuck
     
  13. sigmo

    sigmo Smoking Fanatic

    That's good info, stovebolt!

    I looked at the back of my MES, and it's pop riveted in place.  So to get to what I wanted to look at, I'd have to drill out the rivets. I'll look closer when I've got some time.  Maybe there's an easier way to get into it.  I don't relish totally voiding my warranty just yet.  I've only had the unit for a week or so!  Then again, curiosity will eventually get to me, I'm sure!

    I'm pretty sure I can figure out what is what going to the connectors for the controller board.  I'm curious as to what kind of sensors are in the meat probe and the compartment probe.

    Meanwhile, I've got some pork chops that need to be smoked, and I just got my order from A-Maze-N today.  So I'm going to put this gadget to some good use even if it is out of calibration! 
     
  14. rabbithutch

    rabbithutch Master of the Pit OTBS Member SMF Premier Member

    Sigmo!

    You outdo yourself with every post!

    Thank you very much! Your experience and expertise are very helpful to everyone . . . especially those like me who know so little about the subject.

    Your information will help me be a better smoker!

    Thank you for spending the time to answer our questions.

    . . . and don't void your warranty on my account, please. :biggrin:
     
  15. russg

    russg Fire Starter

    Nice work.   Have you tried the test without the tinfoil?

    Have tried sharing this with MB?

    thanks for all your research.  MB needs you.

    Q to you!
     
  16. smoker21

    smoker21 Meat Mopper

    Thank you for taking the time to experiment and share with us your findings.

    Your numbers are similar to mine, but I just set mine about 15 degrees lower and eat!

    Thanks again.

    JD

    <<Reference Thermometer Reading ----- Smoker Controller Reading

    66.8 ----- 66

    100.9 ----- 97

    131.5 ----- 145

    150.3 ----- 166

    191.6 ----- 203

    245 ----- 262

    262 ----- 280>>
     
  17. smoker21

    smoker21 Meat Mopper

    Oh yeah,

     I always use a thermometer before I pull anything out of the smoker!

    JD
     
  18.  I think you will find the main board under the small cover on the underneath of the smoker. Just the element and thermal sensors under the back.

     Chuck
     
  19. Sir, please take the MES 40 back to where you bought it. I had two in two weeks. Took both back. They were horrible quality and Masterbuiltbwanted me, yes me to work on it for them. Change door, change wood tray, change element then change out cabinet which meant change door again, element again, tray holders, trays, controller, wheels, handle. Forget it. A trip an hour to but it, another to exchange that one and another to return it. I'm done with them and will use a wsm.
     
  20. russg

    russg Fire Starter

    Cat,  what was the model number on the 40.

    11, or 12?

    Thanks
     

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