Back in the days of WWII, aircraft cockpits had few dials (gauges) and each was connected to any individual part of the aircraft engine. As aeroplane design improved so did the number of gauges in the aircraft cockpit.

Overtime, the aircraft cockpit got so crowded with gauges that it was impossible to keep track of all the information that was being displayed. The pilot would look at the gauges that were critical to the flight and just eye-ball the rest and hope for the best. These gauges did not have any alarm system so, more often than not the flight crew usually found out about a problem the hard way - when the engines began to ‘cough’ and sputter.

It is said that necessity is the mother of invention and clearly, when it came to the post WWII aircraft, there was an urgent necessity to improve the way information was displayed in the cockpit.

The one area that technology leap-frogged, was in electronics. The first super computer was invented and it could analyse millions of bits of information every second. So instead of continuing to use analog gauges, aircraft manufacturers and after-market component makers such as J.P. Instruments, began to see electronics and digitization as an ideal way to display engine data.

But before the humble analog gauge went digital, there was need to improve the way data itself was collected and transmitted. Enter the modern sensors.

Earlier Aircraft Sensors were thicker than your fingers and slow to react. Worse, some had mini moving parts (e.g. fuel sensor) inside them that would get stuck during flight. Around the time electronics leap-frogged, new space age technology gave birth to space-age materials that helped overhaul the aircraft engine sensors.

The new sensors became ultra slimline, responded to changes very fast and became more accurate. Simultaneously, the cables that transmitted the data too became ‘Slimline’ and interference-free.

Enter the new and modern slim line gauges (so called because they were less than two inches in height). The feed coming directly from the sensor was attached to each slim line gauge. So, you had a slim line gauge for OAT, Voltage, Oil Temp Probes, RPM Sensor, Manifold Pressure Sensor, Fuel Pressure, Oil Pressure, TIT and so forth.

How Slim Line Gauges work

The individual sensors pick up the data directly from the engine and transmit it as a voltage via wires to the individual slim line gauge for which it is meant. The electronic board and IC circuit onboard the slim line gauge interprets the incoming voltage, converts it into a meaningful number and displays it on the screen. The display was bright enough to be seen even with the sun directly behind the pilot.

A new amazing feature was added into the slim line gauge – thanks to its IC circuit, it could compare the incoming data with pre-entered data coded into the IC chip. Two or three LED bulbs were added to the gauge. So, for example, if the RPM Sensor count was normal, the green LED bulb would light up. If the RPM went up the yellow LED bulb would like up and if the count exceeded specified limits, the red LED bulb would light up. This was a huge relief for the pilot as he only needed to look at the gauge if any LED other than green lite up.

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