The Bar Graphs section contains nine dedicated 12 segment bar graphs with digital display. The default displays are (left to right, top to bottom):  

• Oil temperature
• Oil pressure
• Fuel pressure
• Bus voltage
• Amps load or charge/discharge
• Outside air temperature (or owner selectable )
• Fuel flow, units per hour
• Left fuel quantity (or owner selectable)
• Right fuel quantity (or owner selectable) 

The top of the bar is redline and the bottom of the bar is zero for O-T, OP, F-P, amps load. For amps charge/discharge the center of the bar is zero and the top and bottom is redline charge and discharge, respectively. For volts the top of the bar is high redline and the bottom of the bar is low redline.
The top of the bar for Fuel Flow is set by the MAX FF parameter. The white horizontal line indicates  freezing for OAT. The ranges and alarm values are user settable.

Basic Scanner Options

Let’s examine the scanner section analog display. Central to the display is the exhaust gas temperature— or EGT— bar graph presentation. The height of each column represents the EGT. The last column shows turbine inlet temperature. The range of the EGT columns is red line at the top down to one half of red line at the bottom. This is called the percentage view because you are looking at a percentage of red line. The Normalize view allows you to see small, subtle changes in temperature. When you change to the Normalize view—hold the Lean Find button for three seconds all column heights are set to the identical half-height. Any changes are shown as an increase or decrease in column height. A one-bar change in column height represents a 10 degrees change.  

The Normalize view permits rapid visualization of EGT trends, rather than a percentage of red line. The missing segment in the column represents the cylinder head temperature. Above each column is a number corresponding to the engine cylinder number. The rightmost column displays turbine inlet temperature. Beneath the bar graph is the alphanumeric display. A single index dot above one column indicates which cylinder is being displayed on this numerical display. When the index dot is beneath a cylinder number, 1 through 6, the digital display shows the EGT on the left four digits and the CHT on the right three digits. Two other derived measurements are shown in this display:

• The rate of shock cooling of the most rapidly cooling cylinder, in degrees per minute. Lycoming recommends that you keep this value below 50 degrees per minute.
• The difference between the hottest and coolest exhaust gas temperatures.

EGT and CHT

EGT is shown on the first four or six Scanner bar graph columns. These are labeled 1 through 4 or 1 through 6 above the columns. The lower limit of the graph range represents half of the TIT alarm red line (default is 825°F) and the top of the range represents alarm red line (default 1650°F). The numerical value of the EGT is shown on the left side of the digital display for each cylinder when there is a dot under one of the cylinder numbers above the column—cylinder 2 in this example. There are two views: Normalize view levels the EGT columns and increases the sensitivity of the Scanner bar graph columns to 10° per segment. To enter the Normalize view, hold the LeanFind button for three seconds. The NRM icon will be displayed above the Scanner section. Hold the LeanFind button for three seconds to return to the Percentage view.

The Cylinder Head Temperature—CHT—is represented by a missing segment in the Scanner bar graph column. If the EGT is too low for there to be a missing segment, the CHT is represented by a lone segment in that column. The scale is shown to the left side of the columns. The numerical value of the CHT is shown on the right side of the digital display for each cylinder when there is a dot under one of the cylinder numbers above the column.

Buttons

There are four buttons on the front panel. From left to right they are the STEP button, the Lean Find button, the GMT button, and the EGT fuel flow button. Ten minutes after the EDM-900 is turned on, it will automatically index through all measurements.

Tapping the STEP button will always take you into the manual indexing mode. Here you can observe each measurement value for as long as you want. To the resume the automatic indexing, tap Lean Find and then tap STEP. To switch between the percentage view and the Normalize view, hold the Lean Find button down for five seconds. The GMT button displays the time in the lower left scanner section. It also shows to which measurement each of the nine bar graphs is configured.  You have a choice of three display indexing options as selected by the EGT-FF button.

• The EGT position will display only temperature-related measurements
• The FF position will display only the fuel flow-related measurements, and
• The ALL position will display all measurements.

The display indexing option does not affect the bar graph display, nor does it effect the alarms. Any alarm, such as an over temperature alarm will immediately display the alarm message regardless of which display indexing option is selected.

Lean Find Mode

In a piston engine only a small portion of the energy from combustion produces movement of the piston during the power stroke. The majority of energy passes into the exhaust pipe as hot gasses. By monitoring the temperature of these exhaust gasses you will have an indication of the quality of the combustion process. Low compression, non-uniform fuel distribution, faulty ignition, and clogged injectors diminish the efficiency of the combustion process that generates power. From the cockpit you can adjust the fuel/air ratio by a process called leaning. Retarding the mixture control changes the fuel/air ratio and hence the resulting Exhaust Gas Temperature (EGT).

TIT

To toggle between Percentage and the Normalize views, hold the LF button for three seconds until the NRM icon toggles. The analog display becomes half height and the display changes to the Normalize view. Selecting the Normalize view does not affect the digital display nor alter the measurement sequence. The scale of the CHT display—described later—is not affected by the Normalize or Percentage view. You may select the Normalize view in either the Manual or Automatic mode. Normalize view is most helpful for engine trend monitoring of each cylinder’s operation during cruise. When using the Normalize view during engine run-up, a fouled spark plug will appear as a higher column. A common misapplication is to be in the Normalize view and then change your power setting, causing all columns to go off scale, high or low. Select the Percentage view before adding or reducing power. Always select Percentage View when beginning your descent.

As the mixture is leaned, EGT rises to a peak temperature, and then drops as the mixture is further leaned. Peak power occurs at a mixture using more fuel than at peak EGT. Best economy occurs at peak EGT. Accurate leaning yields optimal engine temperatures. By being able to precisely adjust the mixture, your engine can produce either the best fuel economy or maximum power, whichever you choose.

The EDM-930, Engine Data Management System monitors the following:

Hands-free, automatic scanning All programming done from the Front Panel LeanFind™ finds the first and last cylinder to peak with true peak detect eliminates false peaks Displays both leaned temperature below peak and peak Battery voltage with alarm Amperes (load or charge/discharge meter) Programmable alarm limits Normalize view Exhaust Gas Temperatures (EGTs) to stable 1°F resolution DIF low to high EGT with alarm EGTs to stable 1°F resolution Shock cooling monitored on every cylinder Shock cooling monitored on every cylinder User selectable index rate Fast response probes Non-volatile long term memory Records and stores data up to 30 hours Post-flight data retrieval Download to Palm™ Computer

Data retrieval software Oil pressure Oil temperature Outside air temperature Fuel level Fuel Flow Solid-state rotor fuel flow transducer Fuel quantity in gallons, kilograms, liters, or pounds Low fuel quantity alarm Low fuel time alarm GPS interface Instantaneous fuel flow rate Total amount of fuel consumed Total fuel remaining Time to empty at the curent fuel flow rate RPM and manifold pressure Automatically calculates percent horsepower History of extreme values during previous flight Hobbs® timer