Innovate Motorsports ST-12 - Manual (Page 14)

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5 Internal Sensors
The ST-12 can be programmed directly through the setup buttons on the ST-12. LM Programmer
software version 3.05 (or later) allows you to program the ST-12 via the LM Programmer software. This
is necessary for some of the more advanced functionality of the ST-12. Some of these advanced
functions like speed sensing, frequency sensing, custom RPM, ignition advance and so on require more
user input data that cannot be supplied by the simple 3-button interface of the ST-12.
5.1 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. The "Type K" thermocouple included in the ST-12 kit is composed of Cromel and
Alumel; one lead being made of each ( the red and yellow leads ). Do not look in the box for a
thermocouple sensor to put onto the end of the thermocouple wire. You can use the wire AS the
sensor or use the wires to attach to a Type K thermocouple.
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 ST-12 terminals. The ST-12 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 ST-12 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 confusing 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 ST-12, 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 ST-12. 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 connect the thermocouple probe to the ST-12. You