Calculating Altitude height in Centimeters from Millibars

[Camerart]

Hi,

I have a project that needs an altitude calculation from the sensor I'm using that outputs Millibars.

Can anyone help please?

Most of the calculations I've seen result in Feet.

Cheers, Camerart.

[sethoflagos]

When I was at school there were 30.48 centimetres to one foot, so maybe just multiply the result of your calculation by 30.48?

Or is the input to your calculation not in millibars either?

 

[exchemist]

2 hours ago, Camerart said:

Hi,

I have a project that needs an altitude calculation from the sensor I'm using that outputs Millibars.

Can anyone help please?

Most of the calculations I've seen result in Feet.

Cheers, Camerart.

There's a converter here that tells you how to get from a pressure to the corresponding altitude: https://www.mide.com/air-pressure-at-altitude-calculator

[studiot]

You need this information

 

Quote

Altimeters – What do they actually tell you?

Due to the historic nature of aviation and the fact that it predates GPS systems, avaition doesn’t use “absolute height” (that which you could measure with a tape measure) but “Barometric Altitude” based on the decreasing atmospheric pressure as you ascend.

Barometric Altitude infers height as you ascend upwards based on a standard model of the atmosphere, but this will vary in absolute height depending on the weather, temperature and pressure conditions for the day.

The ICAO (International Civil Aviation Organization) Standard Atmosphere assumes a surface pressure of 1013.2mb dropping at approximately 1mb per 30′ as you ascend and a surface temperature of 15°C dropping at 2°C per 1000′. If, on a particular day, the atmosphere followed these “ideal” conditions your (barometric) Altimeter would read your true height (the same as your GPS height) as you ascended, however, this is rarely the case in practice.

As the (barometric) Altimeter is reading altitude based on pressure it needs to be calibrated to a reference value. In days gone by, this used to be done by setting (calibrating) the reference pressure on the “subscale” of your Altimeter, the image below shows this set to 1013mb. Once this reference pressure is set, your Altimeter then displays (barometric) height above this pressure surface. There are three reference pressures that are in general use for calibrating Altimeters and these are referred to as QNH, 1013.2mb (Standard Pressure) and QFE.

 

[Camerart]

9 hours ago, sethoflagos said:

When I was at school there were 30.48 centimetres to one foot, so maybe just multiply the result of your calculation by 30.48?

Or is the input to your calculation not in millibars either?

 

Hi S,

The question is in the title, I should have said Centimeters in the message body.  The input is in Millibars.

I suppose the calculation is still the same as when you were at school!

C

8 hours ago, exchemist said:

There's a converter here that tells you how to get from a pressure to the corresponding altitude: https://www.mide.com/air-pressure-at-altitude-calculator

Hi E,

Again in feet!  I can of course caculate from feet!

C

8 hours ago, studiot said:

Due to the historic nature of aviation and the fact that it predates GPS systems, avaition doesn’t use “absolute height” (that which you could measure with a tape measure) but “Barometric Altitude” based on the decreasing atmospheric pressure as you ascend.

Barometric Altitude infers height as you ascend upwards based on a standard model of the atmosphere, but this will vary in absolute height depending on the weather, temperature and pressure conditions for the day.

The ICAO (International Civil Aviation Organization) Standard Atmosphere assumes a surface pressure of 1013.2mb dropping at approximately 1mb per 30′ as you ascend and a surface temperature of 15°C dropping at 2°C per 1000′. If, on a particular day, the atmosphere followed these “ideal” conditions your (barometric) Altimeter would read your true height (the same as your GPS height) as you ascended, however, this is rarely the case in practice.

As the (barometric) Altimeter is reading altitude based on pressure it needs to be calibrated to a reference value. In days gone by, this used to be done by setting (calibrating) the reference pressure on the “subscale” of your Altimeter, the image below shows this set to 1013mb. Once this reference pressure is set, your Altimeter then displays (barometric) height above this pressure surface. There are three reference pressures that are in general use for calibrating Altimeters and these are referred to as QNH, 1013.2mb (Standard Pressure) and QFE.

Hi S,

There is a BASE with Altimeter and a REMOTE with Altimeter, the REMOTE will compare the BASE pressure, as a reference, and note the difference.  This is all I need.

I found a calculator, if there are no better calculation here, thanks.

http://www.endmemo.com/physics/pressurealtitude.php

C

[studiot]

5 hours ago, Camerart said:

There is a BASE with Altimeter and a REMOTE with Altimeter, the REMOTE will compare the BASE pressure, as a reference, and note the difference.  This is all I need.

Read the article again properly.

It also gives you a direct standard conversion factor in the absence of calibration.

[Camerart]

10 hours ago, studiot said:

Read the article again properly.

It also gives you a direct standard conversion factor in the absence of calibration.

Hi S,

Do you mean the '1mb per 30′ ' bit?

C

[studiot]

2 minutes ago, Camerart said:

Hi S,

Do you mean the '1mb per 30′ ' bit?

C

Quote

The ICAO (International Civil Aviation Organization) Standard Atmosphere assumes a surface pressure of 1013.2mb dropping at approximately 1mb per 30′ as you ascend

So it tells you the standard surface pressure in millibars and the rate of fall with altitude (in feet).

Clearly if you were able to ascertain that actual pressure at any particular time either at the surface or at a known altitude you could use that to recalibrate the surface pressure and continue to calculate the pressure at other altitudes using the same standard pressure lapse rate.

 

Does this help ?