hobbsy
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| posted on 13/6/10 at 02:02 PM |
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EGT Probe (k type thermocouple) - mounting boss? Circuitry?
I've got a channel left on my Innovate SSI-4 so I thought I might as well log exhaust gas temp. This might give me an indication of if the lean
AFR's I'm seeing are causing things to get dangerously hot on a cruise.
I've already got a k type thermocouple kicking around I just need a mounting boss and an amplifier circuit.
The bosses are usually a compression fitting, see the bottom of this page:
http://www.motorsportsinnovations.com/egt.htm
Anyone know where I can source these from in the UK?
Also I need to sort out a circuit. There is a chip that pretty much sorts this out, an AD595, see:
http://www.analog.com/static/imported-files/data_sheets/ad594_595.pdf
This will give me 10mV per degree C. So 500 deg C = 5V, so I'll have to reduce this as the SSI-4 only logs up to 5V.
Anyone built a similar circuit - the datasheet makes it look every simple, its all on the chip.
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MikeRJ
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| posted on 13/6/10 at 02:48 PM |
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The AD595 pretty much does everything for you, it makes using a thermocouple much easier.
Note that you will need more than a 5v supply for EGT applications (since the output will have to exceed 5v at the upper end of the range).
Also make sure that the point where you terminate the thermocouple is physically close to the AD595 since the cold junction compensation is built into
the IC, so the temperature of the IC and the cold junction must be as close as possible for accurate results.
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hobbsy
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| posted on 13/6/10 at 02:50 PM |
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I read the part about needing more than a 5V supply. It can take up to 30V IIRC so would a straight feed from the battery be ok?
Just trying to blag some samples direct from AD but part of their website is down for maintenance.
Just need to find a compression boss to fit my thermocouple in to.
Guess I should did it out and check its diameter.
Cheers for your help.
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hobbsy
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| posted on 13/6/10 at 02:56 PM |
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Also I've asked the guy selling these if it has a voltage output that is similar to the 10mV per deg C that the AD595 supplies as it would be
useful as a gauge at the same time.
May buy one anyway at that price!
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250559826626
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hobbsy
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| posted on 13/6/10 at 03:04 PM |
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Just found a circuit that includes the extra bits to bring down the output voltage. It was from p142 of the Innovate Logworks manual.
In this case 5V is now 1100deg C (0V is 0deg C)
 
Rescued attachment ad595_circuit.jpg
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Volvorsport
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| posted on 13/6/10 at 03:38 PM |
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we use tcdirect for our EGT probes .
my digital voltmeter can read them , altho it doesnt log anything .
what size bosses do you need ?
www.dbsmotorsport.co.uk
getting dirty under a bus
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MikeRJ
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| posted on 13/6/10 at 04:16 PM |
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quote:
Originally posted by hobbsy
I read the part about needing more than a 5V supply. It can take up to 30V IIRC so would a straight feed from the battery be ok?
You might get away with this, but it's not ideal. Voltage spikes in automotive systems can easily exceed 30v, so I would include some
filtering/voltage clamping at a minimum. Some as simple as a series resistor, a zener shunt (e.g. ~15v) and a capacitor for decoupling would provide
a reasonable level of protection.
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hobbsy
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| posted on 15/7/10 at 11:26 PM |
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If anyone want to build their own k type amplifier circuit for datalogging etc then I found some cheap(er) AD595's on eBay, here:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250660448967
They are quite possibly used but are about 1/2 price to what I can get them for elsewhere and free postage...
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