TEMPERATURE AND
RELATIVE
HUMUDITY
MEASUREMENT
INSTRUMENTS
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Hello, I want to show you the
various instruments we use at
Fresh or Freezing to measure
temperature and relative humidity
and talk about how we maintain
and test them.

We use different instruments to
measure temperature and relative
humidity.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
Let’s look at thermometers first.

This is a dial thermometer.

This is a glass stem thermometer.

These are electronic solid state
thermometers.
Your workplace may use some or all of these.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

For a thermometer to be of
use it must be accurate.
There are two ways to test
a thermometer for
accuracy:
 An ice and water mix
(O C) and compare
your readings.
 Steam
(100 C) and
compare your
readings.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

This is an ice and water
test. We normally work on
systems that are close to
0 °C. So it is more
sensible to use the ice and
water method to
check/calibrate
thermometers.

Be very careful when
testing as both methods
are dangerous – you can
get cold burns as well as
hot burns.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence


When taking readings, be careful.
You will be working on an operating
unit. You need to be aware of
rotating machinery, as well as the
fact that some components will be
very hot or cold.

The techniques and sometimes the
locations for taking temperatures will
vary from thermometer to
thermometer.
You need to be careful to ensure that you make sure the
sensing element or bulb is actually in contact with the
component whose temperature you are trying to measure.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
There are a few points to
remember about measuring
relative humidity. To measure
relative humidity both wet bulb
and dry bulb thermometers are
needed. Usually both types of
thermometers are mounted in a
frame with the wet bulb
thermometer covered with a wet
wick.
 A device mounted in a common frame is called a sling
psychrometer. These are available in a number of styles
using either normal bulb type thermometers or a digital
type thermometer.


Take care to only use distilled water for wetting the wick
as non-distilled water will give incorrect readings
because of impurities in the water.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Sling psychrometers are usually
rotated at approximately two to three
times per second. But check the
instructions for each sling
psychrometer, just to make sure of
the rotation rate required.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

This is a digital
psychrometer.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Most of the instruments are
fragile so we need to store and
maintain them properly so they
give us accurate readings. I
always make sure they are clean
and placed in their correct
storage place when I’ve finished
using them.

Cleaning normally means
cleaning the sensing bulb of the
thermometer. This helps control
contamination between products
as well as providing accurate
readings.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence