flyrotary@lancaironline.net Mailing List Archive

So Finn. The fuller story is. I’m thinking I need to make up a string of 5 amps for my 5 transducers that I have already, to condition the few millivolts to 0-3.3v for a pic micro or the sort. Then I’m thinking how do I read and log the data. But I’d like it synced with the dynon log data which is brilliant. Look at a graph with pressures along side temps and speeds and altitudes….. And then I think of the abundant excess EGT inputs that are used to that kind of millivolt input all connected and logged and displayable. Just a bit of configuration and basically no circuit and development time required. Is it to good to be true. Maybe, but indications are its too easy. Brilliant if it works. Steve > On 8 Aug 2020, at 9:39 am, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote: > > Hi Finn > I input a polynomial based on the raw data from the transducer data sheet. > Full scale output is 35mV for 1.45psi. > Offset at 0 reading is on average 20mV. > > But I thought I’d create a polynomial based on a new set of data using the water manometer incase the 'junction flux capacitor' was throwing out the readings to far. > To far would be pretty far, as I’m simply wanting rough numbers for comparison as I play with the cowl flaps etc. > > Does that make sense? > > Steve > > > >> On 8 Aug 2020, at 9:14 am, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote: >> >> Oh, I thought you'd already worked out the polynonmial values. >> >> http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/temperature-measurement/thermocouple/calibration-table#computing-cold-junction-voltages >> >> probably way overkill. >> >> Input from a type K (EGT) thermocouple would expect a maximum of 55mV (1370C +). >> >> So you may need a voltage divider, depending on the max expected outputs from the pressure sensors. >> Then the trick will be to come up with a formula to counteract the chip's calculation. >> >> For the MAX6675 used in the EM3, it appears fairly simple: >> The MAX6675 includes signal-conditioning hardware to >> convert the thermocouple’s signal into a voltage compatible >> with the input channels of the ADC. The T+ and T- inputs >> connect to internal circuitry that reduces the introduction >> of noise errors from the thermocouple wires. >> Before converting the thermoelectric voltages into >> equivalent temperature values, it is necessary to compensate >> for the difference between the thermocouple >> cold-junction side (MAX6675 ambient temperature) and >> a 0°C virtual reference. For a type-K thermocouple, the >> voltage changes by 41μV/°C, which approximates the >> thermocouple characteristic with the following linear >> equation: >> VOUT = (41μV / °C) ✕ (TR - TAMB) >> Where: >> VOUT is the thermocouple output voltage (μV). >> TR is the temperature of the remote thermocouple junction >> (°C). >> TAMB is the ambient temperature (°C). >> >> Fortunately one of the channels in my EM3 is the temp of the PCB where the chip is located (TAMB). >> >> Don't know what chips are used in the Dynon Skyview. >> >> Finn >> >> >> On 8/7/2020 7:14 PM, Stephen Izett stephen.izett@gmail.com wrote: >>> Hi Finn. >>> >>> The pressure transducers I have can measure from memory a differential pressure of about 40” of water. >>> They have a millivolt output and in the process of cooking up a set of amps and thinking about the fact that Ive used up all my Engine Monitor inputs I pondered all those unused EGT and CHT inputs with amplifiers for millivolt input. >>> I thought about the thermocouple compensation, impedance matching and common mode currents from the egt amps (don't really have a handle on these) and decided I probably wouldn't damage them! >>> So I just thought Id try it out. >>> I wired one straight to an egt input and the Dynon 5v supplied, and applied some lung pressure and the dynon display showed some life. >>> I reworked a new Polynomial and she seems to provide a linear output over my lung burst pressure which from memory is a little over 1 psi. >>> I’m not after certifiable numbers but have built a manometer to hopefully roughly calibrate the output by playing with the Polynomial. >>> So lots of ignorance as far as what’s happening with the electrons at the interface but the results look promising and could be so much more helpful and easier than rigging a manometer in the cockpit. >>> >>> Happy to have my party spoilt by someone with knowledge of the compensation circuit used in the EGT amps. >>> >>> Cheers >>> >>> Steve >>> >>> >>> >>> >>> >>> >>>> On 7 Aug 2020, at 11:01 pm, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote: >>>> >>>> On 8/7/2020 10:00 AM, Stephen Izett stephen.izett@gmail.com wrote: >>>>> I worked out that they interface quite nicely without any other circuitry with the Dynon Skyview's surplus EGT inputs via a new Polynomial in the sensor config settings. >>>> I'm thinking of using my unused?? EGT inputs for current (Hall) sensors. >>>> >>>> How did you compensate for the EGT compensation? >>>> >>>> Finn >>>> >>>> >>>> --- >>>> This email has been checked for viruses by Avast antivirus software. >>>> https://www.avast.com/antivirus >>>> >>>> >>>> -- >>>> Homepage: http://www.flyrotary.com/ >>>> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html >>> >>> -- >>> Homepage: http://www.flyrotary.com/ >>> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html >>> >> >> >> -- >> Homepage: http://www.flyrotary.com/ >> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html