InsaneHydraulics - Sergiy Sydorenko © 2009-2011 All Ridghts Reserved
In hydraulic systems temperature is that one property that can tell a
lot, and I mean A LOT! Machines are just like us, people -whenever we
are sick - our temperature changes! A faulty component can be found
through temperature measurement, the condition of a complete hydraulic
system can be evaluated and monitored through monitoring temperature at
key points, faults can be detected at early stages by monitoring the
tank temperature alone - the list goes on... I will definitely elaborate
on this topic in a separate article, but for now it is sufficient to
say that the importance of knowing accurate temperature of hydraulic
stuff makes the temperature reading gear a must-have tool for us - hydraulic doctors.
In the old days our "ancestors" used to apply
contact thermometers for the purpose - which did the job fine, until the
day they got replaced by the non-contact measuring devices - namely the
infrared thermometers. Cheap and practical, these hand held
devices make temperature reading a snap, or a piece of cake, if you
will... However, there is more to these gadgets than just "point
and shoot", and this post is nothing but a couple of hints on what these
devices are and how to use them correctly to get valid readings.
First of - the physics behind. All matter emits
electromagnetic radiation from the surface when its temperature is
above absolute zero, this radiation is called thermal radiation.
Infrared thermometers can "see" this radiation and infer a body's
surface temperature through measuring its intensity. The thing is -
real life components emit this energy at different rates, even when
they are at the same temperature. This quality of an object is called
emissivity, and it is primarily defined by its surface. It is very important
to take emissivity into account to get correct readings. General rule
is - shiny and polished surfaces (like new hydraulic fittings, hose
terminals, or polished valve bodies) are poor emitters, therefore their
temperature will read lower than real, unless compensated for.
The second thing about shiny components is their reflectabilty (which is relatively high, since they are
shiny), due to which an inaccurate reading is possible when they
reflect thermal radiation emitted by another component - in this case
changing the aiming angle of the thermometer will read a different
temperature, even when pointing at the same spot.
There are models of infrared thermometers that allow you to
manually introduce the emissivity coefficient to make readings more
precise. This is a nice feature, but I, personally, instead of adjusting
my test gear for different surfaces, prefer to "adjust" the surfaces
for my test gear. There are two ways to do this - one is to use a dark
masking tape, glued on the spot you want to read, and in this case
you'll have to wait a bit for the tape to heat up to the component's
temperature, and the other way (my favorite) - is to use black matte
spray to "decorate" the area you wish to measure.
Advantages of the latter are - a) you always get the same
finish, which means stable readings, and b) you clearly mark the spots
where you took the readings - which means that next time the temperature
will be read at the same spot. Disadvantages - well, not all
machine owners will like you to graffiti their equipment, even when it
is for their own good, so you'd better ask them before you do...
If you think that this is not that important - take a look
at the pictures to the left (I had to blank out the background, sorry
about that...). As you can see, the readings between the plain and
painted surfaces differ by more than twenty degrees, which is a lot.
Here is a nice article on infrared thermometers for those who want a little more detail.
Infrared thermometers are an essential tool in hydraulic
equipment diagnostics, and I never leave home without one. Every
mechanic working in this field should have one and know how to use it.