Brad Baker
TVWBB Fan
ET-732 probes have longer plugs than the usual mini plug. Any chance you are inserting them too far?
Maverick Probes
- Thread starter Kevin Scott
- Start date
Kevin Scott
New member
No, if you push them in to far, they just lose contact and go dead.... These are not being pushed in all of the way and are reading, the values just bounce about within about a 3 degree window. I just completed a rib smoke of about 5 hrs, the hotter the pit got, the more stable the pit probe read. So Its more annoying then anything else, however, if I were doing a Brisket or Pork Butt, the food probes would be driving me crazy...
Oh Well... The ET-72 probes for food work great......
Oh Well... The ET-72 probes for food work great......
Kevin,
One other thing that can cause this is if your power supply is not a good clean supply. The value read from the thermistor is created by a voltage divider. If the supply for the voltage fluctuates, your resistance reading will fluctuate and your temperature reading will as well. All of this would be caused by a bad power supply. Make sure you have all the caps on your board put in correctly (for the ones that have polarity markings), make sure you have good soldering for all connections. You could even put you meter on the board and measure the voltage to see if you see any fluctuations. Any fluctuations will be exacerbated for the ET-732 probes because they are a higher resistance. This is one reason the ET-72 are easier to get working.
The one other thing I did to give me better results, was to change my resistor out from a 10k to a 22k for the pit probe. This shifts the table to the left, and moves the top knee of the curves down in temperature, thereby giving me more accuracy at lower temperatures. From your saying you see the fluctuations at the higher temperature, I don't think this will help you, but at the cost of replacing a resistor it is pretty easy to check.
Just remember that after you swap the 10k for a 22k, you have to change your configuration settings to tell the HM to use 22k instead of 10k.
Here is a picture of the curves with the two resistors:
dave
One other thing that can cause this is if your power supply is not a good clean supply. The value read from the thermistor is created by a voltage divider. If the supply for the voltage fluctuates, your resistance reading will fluctuate and your temperature reading will as well. All of this would be caused by a bad power supply. Make sure you have all the caps on your board put in correctly (for the ones that have polarity markings), make sure you have good soldering for all connections. You could even put you meter on the board and measure the voltage to see if you see any fluctuations. Any fluctuations will be exacerbated for the ET-732 probes because they are a higher resistance. This is one reason the ET-72 are easier to get working.
The one other thing I did to give me better results, was to change my resistor out from a 10k to a 22k for the pit probe. This shifts the table to the left, and moves the top knee of the curves down in temperature, thereby giving me more accuracy at lower temperatures. From your saying you see the fluctuations at the higher temperature, I don't think this will help you, but at the cost of replacing a resistor it is pretty easy to check.
Just remember that after you swap the 10k for a 22k, you have to change your configuration settings to tell the HM to use 22k instead of 10k.
Here is a picture of the curves with the two resistors:
dave
Kevin Scott
New member
Thanks Dave, I will check this tomorrow night after work. I will start with the power supply, then the resistors. I am about to build-out my final 2 boards (ver 3.2) I think I will make the change that you recommended. I plan to complete one more linkMeter then try my hand at the RasberryPi version. I'm sure I seem like a glutton for punishment but now that I feel comfortable doing the assembly work, The RasberryPi doesn't seem as daunting...
Brad Baker
TVWBB Fan
If I'm not mistaken the 732 probes are higher resistance and at room temp they'd be at the highest value. I'd be interested in seeing what happens if you hold a capacitor in there across the probe connection, say 1uF or something.
Bryan Mayland
TVWBB Hall of Fame
I'd be curious too, if the capacitor would make a difference. I could see it making a difference if the value just randomly switched all over the range, but seeing as it goes up and down in an oscillatory fashion, it seems like it is something else or just a natural product of the high error in the system at that temperature.
What resistance does the probe read at room temperature when not inserted into HeaterMeter and measured with a multimeter? Does it vary with time as well?
What resistance does the probe read at room temperature when not inserted into HeaterMeter and measured with a multimeter? Does it vary with time as well?
Brad Baker
TVWBB Fan
Two probes at 82F: 850 kOhm, 860 kOhm. They take a while to settle out.
Bryan Mayland
TVWBB Hall of Fame
I don't have any ET-732 probes but I hooked up some resistors to give me 940k ohms (~920k ohms on the multimeter). HeaterMeter bounced between reporting 920k, 931k, and 942k, which correspond to 3 ticks of 10-bit ADC. Then I added two more 0.1uF capacitors between AVCC/GND and my probe input/GND to see if it made it rock solid but it did not. It bounced between 920k and 931k and I only saw one 942k so it is possibly more stable with them but definitely not as all over the place as your probes are indicating. You can try that if you want but I doubt it will make a difference.
Brad Baker
TVWBB Fan
FYI: I am using Thermoworks TW362XX spare probes for the TW362B at $8 each. Downside is length - 42".
I measured these values. YMMV, etc.
I measured these values. YMMV, etc.
Code:
Temp(F) R(ohm)
~~~~~~~ ~~~~~~
32.1 815000
212 13000
318 2650Bill D aka Willbird
TVWBB Member
Pardon if this is a dumb question
...but are these probes the same as IGrill probes ?? IE could you use them with an Igrill ??Bill