Vega EMS-1 Operating Manual
Page 51
11.2 EGT/CHT Installation
The EMS-1 provides for up to 4 thermocouple inputs when using the internal eletronics and up 12 thermocouple inputs
when using the optional external RDAC. K, J as well as E-type probes can be used. K types are used for EGT probes
while CHT probes can either be J or K type. E-type probes are seldom used. Probe types are selected in the various “TC
SETUP” menus of the EMS-1.
Important:
Incorrect selection of probe type will lead to an incorrect temperature display.
The EMS-1 will accept both grounded and isolated thermocouple probes. Your only consideration in case of the more
common grounded configurations is that you need to ensure that the thermocouple mounting position (exhaust flange,
etc.) is at the same electrical potential as the negative supply line of the EMS-1.
The thermocouple amplifier is a precision device providing full cold junction compensation. This results in very accurate
measurements providing you install high quality probes. Here are some guidelines:
EGT Probes:
Select probes that are made from 316 stainless steel and that use glass-fiber insulated conductors. Teflon
insulated conductors as found in many cheap probes introduce errors as the insulation melts moving the measuring point
towards the mounting bolt which transfers a lot of heat to the exhaust material. This results in under reading probes. Stay
away from probes that use simple plastic heat shrink sleeving – it does not last. Choose probes that use a generous
amount of stainless steel spring as strain relief. The bolt itself should be stainless steel as well or it will rust very quickly.
CHT Probes:
These are made from washers to fit spark-plug bases. Temperatures are considerably lower so most
thermocouple cables will work without problems. The biggest area of concern should be the connection of the
thermocouple cable to the washer. This often breaks after the spark plug has been changed a few times. Choose a probe
that is suitably reinforced at this point for a long and trouble free life.
EGT and CHT probes supplied by MGL Avionics are of the highest quality. We recommend that you consider using our
probes if at all possible.
EGT and CHT probes use wire made from iron and other basic metals. As a result these probes are not able to withstand
much flexing of the wires due to engine vibrations. Avoid making nice looking coils or similar constructions that will result
in excessive vibration or flexing of the wire. Route the cables from the probe points tightly along suitable engine mounting
points eliminating any chance of unnecessary wire flexing during engine operation.
Warning:
Four stroke engines produce much hotter exhaust gases compared to two stroke engines. Do not use EGT
probes made from lower grade stainless steel (for example 310), these probes will not withstand the high temperatures
and can fail as the metal gets very soft at 800 degrees C. Many four strokes (such as the Rotax 912) will produce exhaust
gases of up to 850 degrees C.
Please note:
The +5V Sensor power output line is unprotected and intended only for the supply
of a hall-effect, optical or gear tooth sensors. Connecting any voltages (such as the 12V supply) to
this line could destroy the instrument. The +5V line may supply currents of up to 50mA. Should
your sensor require greater currents you must supply it from another source.
Please note
: It is essential that a single wire be connected from the minus terminal of the
instrument to the engine block. This wire must not be used to share currents with other electrical
users as this can affect accuracy of readings.
