From: "Charlie England ceengland7@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Temperature sensors
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Date: Fri, 21 May 2021 15:36:25 -0500
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Don't forget to check on whether the EM3 wants grounded or ungrounded 
probes. I forget which is which, but one type of 'meter' will accept 
either style; the other won't.

On 5/21/2021 2:43 PM, Finn Lassen finn.lassen@verizon.net wrote:
> When I made my own engine monitor for my RV-3 back in 1999 I found it 
> easiest to use sensors that output linear 0 to 5V.
>
> So when I got an EM3 from Tracy, I modified it to use such sensors 
> (LM35, TMP35, TC03 and similar ICs). My reasoning was that they were 
> spec'd to accuracy of a couple of degrees over temperature range of 
> interest.
>
> I wondered why the EM3 had 8 EGT and 8 CHT inputs. (Actually in the 
> EM3 the 8 CHT inputs also go into the same MAX6675 chip designed for 
> Type K thermocouple (EGT) wire.)
>
> After several failures and weird readings of LM35's I'm now beginning 
> to see the wisdom of Tracy's approach. And the LM35CAZ is not cheap 
> either.
>
> If you buy a roll of type K thermocouple wire (less than $1/foot), 
> even if it's off a bit compared to an ideal Type K wire,  all 
> measurement points should be accurate relative to each other. And you 
> just need to calibrate one input for absolute accuracy and use those 
> calibration factors for all the other inputs.
>
> I've spent a lot of time trying to figure out why the coolant output 
> from my right radiator is so much lower than the left's. I even made 
> 3/4" cu tubing inserts with 1/4" wells in them for the ICs to make 
> sure I was measuring actual fluid temps.
>
> After swapping the hoses to the radiators,  the coolant out (out from 
> engine) sensor now inexplicably reads lower by more than 20 deg F  
> than the in-engine sensor. Thought it might have been air in coolant 
> near sensor, but lower readings remain after multiple engine runs,
>
> For the CHT inputs, I had bought Type J thermocouple wire, reasoning 
> that it'd be more sensitive than Type K. Well, 50uV/C is really not 
> much better than 41uV/C, and being fed into a  chip that expects Type 
> K really makes it much harder to re-correct (the MAX6675 chip corrects 
> for ambient temp for Type K not J).
>
> So, I think I'll rip out all sensors, order a roll of Type J wire, 
> make and install new sensors: 1/8NPT plugs drilled for 5/32" brass 
> tubing with wire twisted and soldered to the pinched-shut brass 
> tubing. (My old sensors were 1/8NPT plugs drilled for 1/4" cu tubing 
> that the LM35's could fit in.)
>
> Quite a bit of work, but hopefully will pay off in terms of reliable 
> temperature readings. Without those I don't think I can optimize the 
> cooling system.
>
> Hope that others may learn from my mistakes.
>
> Finn
>
>
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