Ambient Pressure vs. Barometer Pressure [FS 2004]

[b3burner]

I made gauges for each of the above parameters and placed them side by side. As I took off and climbed the numbers decreased with altitude at exactly the same rate and read the same thing-- regardless of standard atmospheric conditions (Weather Clear) or otherwise.

I'm curious what the difference is supposed to be between these, and whether there are conditions under which the simulator will display them as different? Or are they in essence the same thing, only Ambient is from the perspective of the Environment and/or Program, and Barometer is from the perspective of a "virtual barometer" onboard the aircraft?

Thanks,

-- John

[flightman]

They are the same thing. A barometer reads ambient pressure. And of course an altimeter is just a barometer essentially.

Did you try adjusting the altimeter baro setting to see if that made any difference to the gauge readings.

Kevin

[b3burner]

Yes, but it made no difference. That is a separate parameter-- Alitimeter Barometer and/or Kollsman setting, which I plan on using later.

Thank you.

[n4gix]

By default the sim loads with "Standard Atmospheric Pressure" of 29.92 inHg. So, it's not at all surprising that you are seeing the same readings from both variables.

Ambient Pressure is an un-corrected report of the pressure at your current altitude.

Barometer Pressure is the ambient pressure corrected for sea-level.

Change the weather to either stormy, snowy, or else use real weather. Compare the two variables now...

[b3burner]

By default the sim loads with "Standard Atmospheric Pressure" of 29.92 inHg. So, it's not at all surprising that you are seeing the same readings from both variables.

Ambient Pressure is an un-corrected report of the pressure at your current altitude.

Barometer Pressure is the ambient pressure corrected for sea-level.

Change the weather to either stormy, snowy, or else use real weather. Compare the two variables now...

Ok, I tried that and the end result was the same. Sea Level pressure always stayed constant for the situation and place, and the ambient and barometer pressure both decreased with altitude (as one would expect), but my main point is that they always stayed the same compared to one another.

I compared Standard/Clear, Heavy Snows, and Real WX, each between San Francisco (elv. 20) and Los Angeles (elv. 134) with gauges for the parameters Ambient (AMB), Barometer (BAR), and Sea Level (SLV) each; and then at ground level and 10,000 ft MSL for each airport. Below is EXACTLY what each gauge parameter output read, without any interpretation from me:

Standard Atmosphere SFO at 20' MSL:
AMB=29.90
BAR=29.90
SLV=29.92

Standard Atmosphere SFO at 10,000' MSL:
AMB=20.58
BAR=20.58
SLV=29.92
------------------------------------------------------
Standard Atmosphere LAX at 134' MSL:
AMB=29.78
BAR=29.78
SLV=29.92

Standard Atmosphere LAX at 10,000' MSL:
AMB=20.58
BAR=20.58
SLV=29.92

=========================================

Heavy Snows SFO at 20' MSL:
AMB=29.54
BAR=29.54
SLV=29.56

Heavy Snows SFO at 10,000' MSL:
AMB=20.21
BAR=20.21
SLV=29.56
------------------------------------------------------
Heavy Snows LAX at 134' MSL:
AMB=29.42
BAR=29.42
SLV=29.56

Heavy Snows LAX at 10,000' MSL:
AMB=20.21
BAR=20.21
SLV=29.56

==========================================

Real Weather SFO at 20' MSL:
AMB=30.09
BAR=30.09
SLV=30.11

Real Weather SFO at 10,000' MSL:
AMB=20.78
BAR=20.78
SLV=30.11
------------------------------------------------------
Real Weather LAX at 134' MSL:
AMB=29.88
BAR=29.88
SLV=30.02

Real Weather LAX at 10,000' MSL:
AMB=20.68
BAR=20.68
SLV=30.02

The differences between sea level pressures, runway level pressures, and 10,000' MSL pressures across weather types and airports appear to be close to identical. The only notable difference was a change in sea level pressure between SFO and LAX when Real WX was being used, but that's to be expected.

In all cases, AMB and BAR were always equal to each other. This leads me to the conclusion that despite the fact that in real life there may be a scientific distinction between "Ambient Pressure" and "Barometer Pressure", for purposes of this simulator, the two measurements are the same.

[mgh]

As a previous poster said, Ambient and Bariometric Pressues are to same, except perhaps for units (in Hg or mb).

What differences were you expecting?

[b3burner]

As a previous poster said, Ambient and Bariometric Pressues are to same, except perhaps for units (in Hg or mb).

What differences were you expecting?

I wasn't sure what I was expecting... that's why I was asking. I thought maybe 'barometer' was a simulation of the actual instrument inside the plane, while 'ambient' was what the simulator officially says the measurement is. I thought maybe any difference was a simulation of any "virtual error" in the instrument-- though I know that was kind of a reach on my part.

My point is, why have these as two separate parameters in the Panel and Gauge SDK if we've established the fact that they are both indeed the same? Just seems to me like there are a lot of redundant parameters in the SDK list-- or is there a reason for that... and I'm just not understanding the reason why?

[mgh]

There are a number of redundant or even unused parameters in the SDK.

One of the first activities in developing a major application is to create a list of variables to be used. This list identifies the varibles, their units, types, limitations etc. It's used as the standard reference for all the programmers working on different parts of the application. It's not set in stone and can be amended as the application develops. The initial list is likely to contain everything that might possibly be needed just in case and also may well contain effective duplicates. In the event some variables may not be used and become redundant; duplicates may have been used by different programmers and so have to be left in.

Given the long history of Flight Simulator, it's surprising that there aren't more anomolies.