Electronics International M-1 Manifold Pressure - Manual (Page 5)

Operation Instructions
M-1
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Instrument:
The M-1 is a precision manifold pressure instrument featuring a 210 degree analog display and a digital
display. These two displays have many advantages over conventional analog gauges as described below.
Also, the M-1 features long-term accuracy and reliability. Since the M-1 does not incorporate any moving
parts (needles, bearings, springs, etc.) there is little to go wrong or wear out. The internal microprocessor assures
accuracy and repeatability.
Analog Display:
The 210 degree analog display provides a quick reference of manifold pressure with respect to its operating
range. At a glance you can get a relative idea of where in the range you are operating the engine and how close to
the maximum limit you are. Precise information is provided in the digital display.
An advantage of the analog display is its ability to emit a green, yellow or red light. With a quick glance you
can determine if you’re operating in a normal, caution or restricted range. Also, when you exceed a maximum
limit the red light will blink 20 times at full intensity to catch your attention and warn you that a maximum limit
has been violated. After 20 blinks the red light will stop blinking and display continuous red so it does not distract
you.
During night operation the analog lights may be too bright. If so, turn the panel light rheostat up and the
analog lights will dim. The red (maximum limit) light will always be displayed at full intensity.
Digital Display:
The M-1 measures absolute atmospheric pressure in the engine’s manifold to .1 inches of mercury. This
reading should not be confused with barometric pressure. Barometric pressure readings are altitude compensated
to sea level. For every 100 feet above sea level there is approximately .1 inches of mercury less manifold pressure
available to the engine. That means at 1000 feet above sea level with a barometric reading of 30.0 inches of
mercury, the maximum manifold pressure available for a non-turbocharged aircraft is 29.0 inches of mercury.
Less manifold pressure means less power.
Two other factors affecting manifold pressure are induction loss and ram air. Induction loss is the normal
drop in pressure across the carburetor and intake manifold. This will lower your available manifold pressure by
approximately 1.0 inches of mercury. Ram air, on the other hand, will increase your manifold pressure. Ram air
is the normal compression of air in the manifold caused by airspeed and dependent on the location of the intake
air pickup point. At 145 knots the maximum increase in manifold pressure available is 1.0 inches of mercury.
3 Rev. A: 6/16/92