Innovate Motorsports LMA-3 - Manual (Page 9)

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3.4 Powering external sensors
If you want to power external sensors, connect a switched 12V supply (switched on when the
cars ignition system is on) to the connection marked 12V on the left side. Connect the connection
marked GND to the cars chassis ground. At the connection marked 5V you can connect external
sensors. External sensors don’t HAVE to be powered by the LMA-3. The 5V output is a
convenience for external sensors when no 5V supply is available. The 5V supply can power
sensors with a total power consumption of up to 300mA.
3.5 Connecting an RPM signal
For RPM measurement you can either connect a tach signal to the CH1+ input or plug an
inductive clamp into the 3.5 mm stereo socket marked RPM. See chapter 6 for RPM
measurement details.
3.6 Connecting Type K Thermocouples
Thermocouples are used to measure temperatures by relying on the phenomena where a
junction of any two different metals ( Copper and Iron, for example ) will generate a small
voltage. This voltage is dependant upon which two metal are used, and the temperature of the
junction. This phenomena is known, formally, as the "Seebeck Effect". Because every junction
of different metals contributes its own voltage into the measurement, it is important to have as
few junctions between dissimilar metals as possible in order to record an accurate
measurement. This is why thermocouple wire is made completely of two different metals. A
"Type K" thermocouple is composed of Cromel and Alumel; one lead being made of each ( the
red and yellow leads ).
To make a thermocouple, strip approximately 3/4" of insulation form one end of the thermocouple
wire. Twist the two exposed metal ends together. You may optionally solder them, also. But
twist them first. Do not solder them in parallel. This will form what is called the "Hot junction".
This "Hot junction" is what you will connect to the surface that you want to measure. This is
usually either: a) under the copper gasket of a sparkplug for cylinder head temperature
(CHT) or, b) clamped to a primary header tube for exhaust gas temperature (EGT).
There is also the "Cold junction." This is where the 2 leads of the thermocouple come together
again at the LMA-3 terminals. The LMA-3 has an internal temperature sensor at the T/C input
terminals. It uses this sensor to "offset" the effect of the "Cold junction" in the measurement.
This is called "Cold junction compensation". Once the effects of the cold junction are neutralized,
the LMA-3 can accurately read the temperature of the "Hot junction" which is the twisted lead pair
at the opposite end of the thermocouple wire.
One thing that is counter intuitive for many people is that the negative side of a thermocouple
wire is always red. There are many different types of thermocouple wire; types K, J and T being
the most popular. All have a red negative lead and a yellow, black, or blue positive lead
respectively. When connection the thermocouple to the TC terminals on the LMA-3, be
sure to connect the yellow lead to the + and red lead to the - terminals.
Several manufacturers offer EGT "thermocouple probes" which are actually inserted into the
exhaust gas stream through a hole in the headers or exhaust manifold. These provide a more
accurate measurement of exhaust gas temperature. They are commonly available in types K
and J. Only type K will currently work with the LMA-3. To use a thermocouple probe, connect
the red and yellow leads of the thermocouple wire to the yellow and red leads of the
thermocouple probe. The junction is inside the probe. You can not use normal copper wire to