CHT measurement via electronic meters

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mousewheels
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Re: CHT measurement via electronic meters

Post by mousewheels » Sun Sep 13, 2009 3:38 pm

4th up - Higher end dual thermometers
Moving up from that $27 dual channel thermometer gives increasing functionality:
  1. Dual Display show both readings
  2. Min/Max and internal clock capture the value, and what time it was recorded
  3. Can work with multiple types of thermocouple wires J, K,T, E, N, R, S.
    That's handy if your bike is already wired for a CHT, but uses something different than a 'K type' thermocouple
  4. Logging function. Manually trigger storage, or set up a periodic timer to capture samples
  5. PC interface - download logged data for review, processing and display
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Fluke 54-II
$369

Temperature accuracy
Above -100 ┬░C: J, K, T, E, and N-type: ┬▒[0.05% + 0.3┬░C]*
R and S-type: ┬▒[0.05% + 0.4┬░C]*

Advantages: Fluke quality, accurate, easy to use, settings are persistent. 1000hr battery life. PC software is not required to review logged data, but convenient.

Disadvantages: Fluke does not include the PC software and IR adapter in the price. That accessory is around $180. Second meter itself is expensive. There are competitors which make logging thermometers, include the PC software, and sell for less. Will post links later. The pictured meter was lightly used, and discounted.

--- Logging example - CHT sensor location ---
Plug sensors are commonly used as well as other mounts around the cyl head. One convenient location is a head bolt. How do the two readings compare? Perfect test for a dual channel logging meter, capturing data on exactly the same run.

Probe installation - Stock 1999 Elite SA50. Rear headbolt, closest to cooling fan. 2nd probe on plug.
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Test run - approx 3 miles, temperature readings are logged every 10 sec
Results: Temperature differences between sensor placements are large. Plug sensor recorded temp peaks on hills that the head bolt location did not register.
Image

Second test - different scooter Yamaha QT50
More testing of CHT probe placement. Different scooter, no forced air cooling. Exact same test route.

Probe installation:
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Results: Temperature differences between sensor placements remains large. QT50 is running hot, better go find that larger jet in the garage...
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Bear45-70
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Re: CHT measurement via electronic meters

Post by Bear45-70 » Sun Sep 13, 2009 3:56 pm

The temp difference is pretty much what I would expect. The plug is directly in the combustion chamber. The head bolt is not.

But from past experience with using a CHT gauge with a switch for selecting the sensors on all 6 cylinder heads locations of a 2 liter race motor, the CHT will only tell you which cylinder you seized in a 2 stroke application. The temps that cause seizing rise to fast and melt the piston top so fast that the gauge can not indicate which cylinder it is before it has done the damage.

My Fluke multimeter has an accessory plug-in adapter to do the temp probe thing, but I never bothered to get it. The shop always had a CHT set-up available for testing.
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mousewheels
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Re: CHT measurement via electronic meters

Post by mousewheels » Sun Sep 13, 2009 4:50 pm

Bear45-70 wrote:The temp difference is pretty much what I would expect. The plug is directly in the combustion chamber. The head bolt is not.
Right, not unexpected. Benefit of the test is to quantify the difference over dynamic conditions.
Bear45-70 wrote:My Fluke multimeter has an accessory plug-in adapter to do the temp probe thing, but I never bothered to get it. The shop always had a CHT set-up available for testing.
If the adapter your need is not the battery powered adapter in this thread (Fluke 80TK) and looks like the pic below, its just a molded banana plug adapter for the K-type thermocouple ends. You could make your own.
Image
The temps that cause seizing rise to fast and melt the piston top so fast that the gauge can not indicate which cylinder it is before it has done the damage.
Right, CHT's are slow, and human response too. For this electronic metering thread, I'm game for anything that can be measured at reasonable cost. EGT sensor is the next thing to add. What else should we look at? Also, are the controls used protecting those $$$ race motors doing their work w/o human input?

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Re: CHT measurement via electronic meters

Post by Bear45-70 » Sun Sep 13, 2009 4:56 pm

Actually EGT (Exhaust Gas Temperature) will tell you more, sooner than an CHT.
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Heat Feedback Loop Control

Post by Wheelman-111 » Sun Sep 13, 2009 5:36 pm

Greetings:

This is where engine tech is today. Even historically rustic Harley-Davidson's current Touring models have a feature to retard timing and even disable their rear cylinder when temps get too high during parade duty. Anything's possible with enough sensors and a computer to conduct everything.
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Re: CHT measurement via electronic meters

Post by elitedio » Fri Sep 25, 2009 10:17 pm

Just another data point. I hooked an old thermocouple up from a gas water heater to my dvm and got about 2ma on the 20ma scale and 2.4 mv on the 200 mv scale. I heated it till glowing with my propane torch. Probably melted the works. It is a cheap DVM but probably still has high impedance. :)
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mousewheels
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Re: CHT measurement via electronic meters

Post by mousewheels » Sat Sep 26, 2009 9:03 pm

elietedio wrote:I hooked an old thermocouple up from a gas water heater to my dvm and got about 2ma on the 20ma scale and 2.4 mv on the 200 mv scale. I heated it till glowing with my propane torch. Probably melted the works.
Thanks - That's an interesting idea - will look into it. It's less expensive than an OEM EGT thermocouple.

Also, am looking at a bolt on thermocouple like below. But am not sure it's a gas tight connection between the probe and nut.
Image

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