G5 questions

[bcg]

I have a single G5 as an AI in my C without a GAD, GMU or OAT sensor so I only get Track, IAS and GS on it.  I would like to get TAS, Winds and MH as well and know it needs the GMU 11 for MH and will need OAT from somewhere to make the calculations.

First question is will the single G5 AI display all this if I've given it OAT and MH?  Assuming that it will show it without the G5 HSI, will an EDM 930 provide that?  I'm replacing my legacy engine gauges with a 930 at annual and plan to interface it with the GPS 175 and the G5, I know it will provide fuel flow and endurance to the GPS but, I'm not clear what else it shares.

[McMooney]

you need the Gad13 + temp probe for oat

yes the gmu 11 provides MH. 

everything is connected via the canbus to the g5, really simple actually.   

BUTTTT, while you're in there and you've installed all that which is most of the g5 system, maybe add the gad 29b and arincs to the gps????

[Ragsf15e]

My edm 930 has temp and gets groundspeed from the gps, but it has no way to display tas or winds as it doesn’t have heading or ias.

I have 2G5s, but do not have temp or winds on them. It is a pretty simple calculator on my Garmin 430 GPS to get that info, however.

[RoundTwo]

If you want higher TAS, make sure to put the OAT in line with the tailpipe. The downside to that is you’ll always be flying with a headwind.

[EricJ]

I have two G5s, an EDM 900, and an IFD550 that all talk to each other.    I don't display winds on the G5, or TAS, but the IFD gets OAT from the JPI, and other air data from the G5.   So I can get TAS, TAT, computed winds, etc., on the same page on the IFD.    I do gave groundspeed on the G5 and it shows magnetic heading at the top of the AI display.  I know it can be configured to show wind, but I get that on the IFD, so I can keep a little clutter off of the G5..    

[bcg]

1 hour ago, McMooney said:

you need the Gad13 + temp probe for oat

yes the gmu 11 provides MH. 

everything is connected via the canbus to the g5, really simple actually.   

BUTTTT, while you're in there and you've installed all that which is most of the g5 system, maybe add the gad 29b and arincs to the gps????

Thanks for the input.  I was hoping I could use the 930's OAT but, it doesn't look like that will be possible.  Bummer but, at least it's only about another $500 for the GAD13 and probe which, in aviation terms anyway, is pretty cheap.

I have an Icarus SAM GPSS for the GPS and STec already and I don't have the G5 HSI, only the AI.  The SAM isn't the best but, it does the job well enough.

[bcg]

40 minutes ago, Ragsf15e said:

My edm 930 has temp and gets groundspeed from the gps, but it has no way to display tas or winds as it doesn’t have heading or ias.

I have 2G5s, but do not have temp or winds on them. It is a pretty simple calculator on my Garmin 430 GPS to get that info, however.

The 175 has the calculator as well, it would just be easier to not have to input anything.  I'm told I can have the 175 do the calculations with the sensor data and that it will get the OAT from the 930 but, I have to go through a couple of screens to see it.  Normally not that big a deal unless it's a little bumpy and then the touch screen leaves a bit to be desired.

[bcg]

26 minutes ago, EricJ said:

I have two G5s, an EDM 900, and an IFD550 that all talk to each other.    I don't display winds on the G5, or TAS, but the IFD gets OAT from the JPI, and other air data from the G5.   So I can get TAS, TAT, computed winds, etc., on the same page on the IFD.    I do gave groundspeed on the G5 and it shows magnetic heading at the top of the AI display.  I know it can be configured to show wind, but I get that on the IFD, so I can keep a little clutter off of the G5..    

I'd love to put the 2nd G5 HSI in and get rid of the old GPSS, the problem is that my NAV radio won't talk to a G5 so then I would want to replace that as well which turns into a huge project and causes the costs to quickly escalate.  If this was the forever plane, I would do it.  Right now though, I don't expect it to be so I have to be more conscientious about my spending on upgrades.

[Ragsf15e]

1 hour ago, bcg said:

The 175 has the calculator as well, it would just be easier to not have to input anything.  I'm told I can have the 175 do the calculations with the sensor data and that it will get the OAT from the 930 but, I have to go through a couple of screens to see it.  Normally not that big a deal unless it's a little bumpy and then the touch screen leaves a bit to be desired.

Yeah, I wish the oat would populate from the jpi930 to the g5 as well but it doesn’t.  My gps (430w) gets oat from the 930 for that tas/wind calc page, but the oat isn’t fed to the g5.

[McMooney]

2 hours ago, bcg said:

Thanks for the input.  I was hoping I could use the 930's OAT but, it doesn't look like that will be possible.  Bummer but, at least it's only about another $500 for the GAD13 and probe which, in aviation terms anyway, is pretty cheap.

I have an Icarus SAM GPSS for the GPS and STec already and I don't have the G5 HSI, only the AI.  The SAM isn't the best but, it does the job well enough.

I used the davtron probe instead of the expensive garmin, seems to work just fine.

temp matches the davtron gage installed on the otherside of the plane so figure it's atleast close to correct.  

[hammdo]

Ditto on the davtron…

-Don

[Vance Harral]

Another +1 on the Davtron C307PS probe.  Many, many G5 installations in the field are using this less expensive probe rather than the GTP59.  Garmin will tell you the GTP59 is TSO'd, used in certified installations up to business jets, and achieves better accuracy than the C307PS.  All that is probably true, but it's not meaningful in a GA piston single, and not worth the extra cost.

[bcg]

7 hours ago, Vance Harral said:

Another +1 on the Davtron C307PS probe.  Many, many G5 installations in the field are using this less expensive probe rather than the GTP59.  Garmin will tell you the GTP59 is TSO'd, used in certified installations up to business jets, and achieves better accuracy than the C307PS.  All that is probably true, but it's not meaningful in a GA piston single, and not worth the extra cost.

So it's the analog probe, not the digital?

[Vance Harral]

3 hours ago, bcg said:

So it's the analog probe, not the digital?

I'm not sure exactly what you're asking here.  Both the Garmin GTP59 and the Davtron C307PS are analog temperature sensors, albeit different technologies.  In fact, all temperature sensors are analog devices.  The whole point of the GAD13 is to convert that analog information from the probe, to digital information transmitted over CANBUS to the G5.

Since I'm feeling nerdy this morning...

An OAT probe is just a metal shell wrapped around an integrated circuit.  In the case of the Davtron C307PS and similar products, the IC is an Analog Devices AD590.  When supplied with a voltage differential across its two pins, this device produces a current that is proportional to absolute (Kelvin) temperature.  Data sheet is available at https://www.analog.com/media/en/technical-documentation/data-sheets/AD590.pdf.  The data sheet shows that the AD590 comes in two flavors, with two different accuracy specs.  Garmin techs like to point out that the "cheap" flavor has a potential accuracy error of +/- 5C (with no external temperature compensation circuit).  They imply their competitors use this cheap configuration, while Garmin uses more accurate hardware.  These claims are probably true, but I argue they're not meaningful - more on that shortly.

In the case of the GTP59, Garmin doesn't publish what IC is inside their probe, but based on the way the GAD13 connects to it, it's almost certainly a 3-wire resistive sensor.  These sensors present a resistance which varies with temperature, across 2 of their leads.  The 3rd lead is just a short to one of the two other leads.  It exists so the controller can measure the resistance of the connecting wires themselves, and effectively subtract that resistance out of the calculation.  I'm sure there are high quality/accuracy versions of these sensors.  But if I were building an experimental, I might try a ten-dollar, hot tub probe, e.g. https://www.amazon.com/Waterproof-RTD-PT100-Temperature-Sensor/dp/B07DP3LYPX/.  At that price, I could buy several units, use the one that tests with the best accuracy in an ice bath, and throw away the others.  Garmin probably doesn't buy hot-tub quality sensors, but they almost certainly qualify incoming units from their suppliers, and reject those outside Garmin's own tolerance limits.  Anyone else can do this too, though.  Again, more on that shortly.

So let's examine the worst case scenario on "cheaping out" with the Davtron probe: if Davtron purchases the cheapest version of the AD590, and you are unlucky enough that the particular unit you get has the worst possible error, and neither you nor Davtron performs any QC testing on the probe, you could get a C307PS that is off by +/- 5C.  At piston airplane speeds and altitudes (including turbocharged airplanes up to the flight levels), a 5C inaccuracy results in a true airspeed error of 1-2 knots, which is not meaningful.  Accuracy is more of a concern if you're talking about whether you'll get airframe icing.  But since it's foolish to assume you're completely safe at +1C and completely in peril at 0C with any temperature probe installation, it's hard to argue this has much operational meaning.  In practice, we start looking outside for airframe icing any time OAT dips within a few degrees of 0C.  So even a 5C inaccuracy is relatively meaningless, other than bragging rights.

In reality, though, I think it's extremely unlikely you'll get a Davtron probe that's off by 5C.  I presume here that Davtron doesn't have a completely stupid manufacturing process.  If my assumption is correct, they assemble the units, then perform some sort of "smoke test" to guard against assembly errors, as well as bad parts received from their IC supplier, just like Garmin.  Such a test would catch, and allow Davtron to reject, the very small number of parts at the worst of the accuracy range.  You'll have to decide for yourself what you think about Davtron QC.  But if you're a cynic about that - and have some patience - you can be your own QC.  Buy the cheap Davtron probe, hook it up on a bench, drop the probe in an ice bath, and return it for another if the temperature it reports is off by more than your personal tolerance.  Lather/rinse/repeat until you get what you want, and proudly proclaim your CB status.

In summary, temperature probes are just a wrapper around an IC supplied from an outside source.  Those ICs have accuracy specs on paper, but in reality the accuracy of the probe you get depends on the QC process used by the manufacturer, which potentially rejects outlying units.  Garmin's process might be better than Davtron, and it makes sense to pay their price if you're manufacturing a $40M bizjet.  For the rest of us, a less expensive solution makes sense; and to Garmin's credit, they support this by supplying an AD590-compatible input to the GAD13.  I think that's an entirely reasonable position for Garmin to take, and I happily supported them in buying their GAD13.  But I also supported Davtron by using their "cheap" probe. 

 

[bcg]

2 minutes ago, Vance Harral said:

I'm not sure exactly what you're asking here. 

 

Davtron lists an analog probe (C307PS you mentioned) and a D307PS digital probe - https://www.davtron.com/product-detail.php?PROBE-12FT-WHT-D-27.  I was just clarifying that it was the analog version.

[Vance Harral]

19 minutes ago, bcg said:

Davtron lists an analog probe (C307PS you mentioned) and a D307PS digital probe

Thanks for the clarification.  Yes, the C307PS is what you want.  It is specifically called out by name in the G5 installation manual.

The D307PS has an integrated A/D converter somewhat like the GAD13.  But it converts the current produced by the AD590 to 1-wire digital protocol, rather than the CANBUS protocol needed by the G5.  Other Davtron products can receive this 1-wire protocol, e.g. their M303 display.  I don't know if any avionics manufacturer other than Davtron supports 1-wire.

It's interesting that the D307PS is less expensive than the C307PS, given that by definition it must contain more "stuff" inside.  Maybe the D307PS uses an IC which integrates the A/D converter, and is manufactured in greater bulk such that the component is cheaper despite being more sophisticated.  Or it might just be a certification or "what the market will bear" thing.  Might also be a loss leader to try to get you buy the M303 or other Davtron products.