The EM3 uses the AD595 chip. EM2 uses
both a AD595 and AD594 chip.
Not sure why doesn't use both in the EM3. I guess he figured he
could compensate with software when using type J thermocouples.
Both with mutiplexers in front.
https://www.analog.com/en/products/ad595.html#product-overview
https://drive.google.com/open?id=1PlOVARBeXjEmB4iqhMjyHMy02E5-C24j
So you have differential inputs with a curve that matches a type K
thermocouple. And compensated for temperature at the input pins
(circuit board where you connect the thermocouples).
Should be possible to connect the MPX10's to the spare EGT/CHT
inputs and play around with the offset and scale factor. However,
I don't think thermocouples are linear, so you won't be able to
get an accurate pressure readout over a bigger range. But if you
use data logging I would imagine it's possible to correct the data
using the thermocouple curve (or formula?). But for your purposes
absolute values will not be as important as relative values.
Come to think of it -- may be simpler to connect a reference MPX10
to one of the differential inputs and the measuring MPX10 to the
other differential input on a channel.
Anyhow, you now have all the data to make it work :)
Finn
On 1/8/2020 12:50 AM, Stephen Izett
stephen.izett@gmail.com wrote:
Hi people
I???m wondering about the possibility of using the EM3???s EGT CHT differential inputs to read some pressure transducer signals.
See MPX10 specs below. I have a handful of them and I???m keen to read some pressures in the cowl in order to plan and tune cowl flaps and any changes to intake sizes.
Its just the EM3 is already there and if not can display the data with some calibration it will save me building up a seperate system.
I haven???t any background in thermocouples and their signal conditioning.
The MPX???s output (20-55mV) which appear to fit within the range of K & J type thermocouples, but am I missing something in the amp/conditioning circuit in the EM3???s EGT and CHT inputs?
I noted that many thermocouples have a grounded input and thermocouple amp/conditioning IC???s have reference junction temp inputs.
Can any of you guys help me here?
Cheers
Steve Izett
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