MSD Trigger Pickups: Magnetic vs. Optical Tech Bulletin - Manual

MSD’s Tech Bulletins are designed to give you a more in-depth
understanding of the ignition system and its components. If you have any other questions about the
subject or MSD products you can contact our Customer Support Department at (915) 855-7123 or
email your questions to [email protected].
Tech Bulletin Tech Bulletin
Trigger Pickups: Magnetic vs. Optical
There recently has been debate concerning trigger methods used in distributors. The two most common racing pickups used
in distributors are a magnetic pickup and optical pickups.
Both pickups have been available for a number of years and in a variety of applications. The pickups perform the same job,
triggering the ignition at the precise moment, just in a different manner. Both pickups accomplish their goals, however in the
long run for endurance and accuracy throughout the entire rpm range, the magnetic pickup is the best choice.
OPERATION
The MSD magnetic pickup acts as a generator creating a strong, clear signal. It is made up of windings placed in a magnetic
field to produce an electric signal. With this simple design, there are only two wires to connect - so there are fewer connections
to be concerned about.
When a pole, or the paddle of the reluctor passes in front of the pickup, a voltage is created. As rpm increases, the signal
strength increases as well giving it fast rise/fall times. At high rpm, this signal can reach well over 50 volts. This trigger signal
will be addressed later in the text.
A magnetic pickup is very reliable at high temperatures and in extreme conditions. Moisture, oil or mild debris will not affect
the trigger signal making it the best choice in long races. Also, ozone and static electricity that builds inside the distributor cap
will not affect the pickup’s output signal.
An optical trigger uses a Light Emitting Diode (LED) and a photo receptor. The LED’s light beam is interrupted by a wheel that
is connected to the distributor shaft. There are “windows” that let the LED beam shine through to the receptor which is respon-
sible for producing the trigger signal. This signal is then usually processed into a 12 volt signal and then sent to the ignition as
a trigger signal. This requires a three wire connection to each pickup; a 12 volt source, ground and the trigger output wire.
Magnetic Pickup
Withstands Higher Temperatures (+150°C)
No Mechanical Parts to Wear Out
Not Affected by Moisture or Debris
Simple, 2-Wire Connection
Creates a well defined Zero Volt reference
point for each firing that is not affected
by heat
Handles Static Electricity
Optical Pickup
Affected by Higher Temperatures (+100°C)
LED will Wear Over Time
Affected by Moisture and Debris
Three Wires; 12 volts, Ground and Signal
Reference Point is fixed and can be affected
by temperature changes
Susceptible to Static Electricity
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TRIGGER PICKUPS: MAGNETIC VS. OPTICAL TRIGGER PICKUPS: MAGNETIC VS. OPTICAL