Understanding Altitude Indicators (Altimeters)

This page covers the Altitude Indicator, also known as the Altimeter. The Altimeter is used to measure altitude and is widely used in the avionics domain. We’ll also mention some vendors who provide altimeters used as altitude indicators.

The equipment used to measure the altitude of an object above a fixed level (i.e., sea level) is known as an Altimeter. A major application is determining the height of an airplane flying above the earth to avoid obstacles such as mountains and other airplanes. Moreover, it’s advisable to fly at a high altitude due to the thinner air, which requires less fuel as it asserts less resistance. This optimal region can be found by knowing the altitude level.

There are two main methods to measure altitude:

Methods to Measure Altitude

Method 1: Measure air pressure and determine altitude from this.

This method relies on the principle that air pressure decreases with increasing altitude. By measuring the air pressure surrounding the aircraft, the altimeter can calculate the corresponding altitude.

Method 2: Transmit a radio frequency wave from the airplane towards the earth and measure the round trip time.

We know that radio waves travel at the speed of light (approximately 3 x 10^8 m/sec). By measuring the time it takes for the radio wave to travel to the ground and back, we can calculate the distance, which gives us the height of the airplane above the earth. The figure above visually explains this concept.

The most common altimeters used in avionics are known as aneroid barometers. They display height by measuring pressure. This type of altimeter uses a hollow box that expands and contracts based on pressure decrease and increase. This movement consecutively moves the pointer based on the change in air pressure.

Vendors of Altimeter or Altitude Indicator

The following are some of the vendors of altimeters or altitude indicators:

• HTC AL-7000 (measuring range: 0-5000 meters/580-1040 hpa)
• Swastik Scientific Company, MUMBAI, INDIA
• L.J. Engineering, Inc. CA
• Apex Instruments, Inc., NC
• RIEGL, FL, USA